[PATCH v4] displif: add ABI for para-virtual display

[PATCH v4] displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

This is the ABI for the two halves of a para-virtualized
display driver.

This protocol aims to provide a unified protocol which fits more
sophisticated use-cases than a framebuffer device can handle. At the
moment basic functionality is supported with the intention to extend:
  o multiple dynamically allocated/destroyed framebuffers
  o buffers of arbitrary sizes
  o better configuration options including multiple display support

Note: existing fbif can be used together with displif running at the
same time, e.g. on Linux one provides framebuffer and another DRM/KMS

Future extensions to the existing protocol may include:
  o allow display/connector cloning
  o allow allocating objects other than display buffers
  o add planes/overlays support
  o support scaling
  o support rotation

Thank you,
Oleksandr Andrushchenko
Oleksandr Grytsov

Oleksandr Andrushchenko (1):
  displif: add ABI for para-virtual display

 xen/include/public/io/displif.h | 847 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 847 insertions(+)
 create mode 100644 xen/include/public/io/displif.h

-- 
2.7.4


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[PATCH v4] displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

This is the ABI for the two halves of a para-virtualized
display driver.

This protocol aims to provide a unified protocol which fits more
sophisticated use-cases than a framebuffer device can handle. At the
moment basic functionality is supported with the intention to extend:
  o multiple dynamically allocated/destroyed framebuffers
  o buffers of arbitrary sizes
  o better configuration options including multiple display support

Note: existing fbif can be used together with displif running at the
same time, e.g. on Linux one provides framebuffer and another DRM/KMS

Future extensions to the existing protocol may include:
  o allow display/connector cloning
  o allow allocating objects other than display buffers
  o add planes/overlays support
  o support scaling
  o support rotation

Note, that this protocol doesn't use ring macros for
bi-directional exchange (PV calls/9pfs) bacause:
  o it statically defines the use of a single page
    for the ring buffer
  o it uses direct memory access to ring's contents
    w/o memory copying
  o re-uses the same idea that kbdif/fbif use
    which for this use-case seems to be appropriate

==================================================
Rationale for introducing this protocol instead of
using the existing fbif:
==================================================

1. In/out event sizes
  o fbif - 40 octets
  o displif - 40 octets
This is only the initial version of the displif protocol
which means that there could be requests which will not fit
(WRT introducing some GPU related functionality
later on). In that case we cannot alter fbif sizes as we need to
be backward compatible an will be forced to handle those
apart of fbif.

2. Shared page
Displif doesn't use anything like struct xenfb_page, but
DEFINE_RING_TYPES(xen_displif, struct xendispl_req, struct
xendispl_resp) which is a better and more common way.
Output events use a shared page which only has in_cons and in_prod
and all the rest is used for incoming events. Here struct xenfb_page
could probably be used as is despite the fact that it only has a half
of a page for incoming events which is only 50 events. (consider
something like 60Hz display)

3. Amount of changes.
fbif only provides XENFB_TYPE_UPDATE and XENFB_TYPE_RESIZE
events, so it looks like it is easier to get fb support into displif
than vice versa. displif at the moment has 6 requests and 1 event,
multiple connector support, etc.

---
Changes since v3:
 * add clarification on buffer's size/depth/format and
   connector's resolution
 * move be_alloc feature into domain's configuration
   to allow more use-cases and freedom (e.g. for 1:1
   mapped domains there may be no need to request backend
   to allocate buffers, while for the rest it may make more
   sense)
 * rename XenStore entries:
     ctrl-ring-ref -> req-ring-ref
     ctrl-channel -> req-event-channel
     event-ring-ref -> evt-ring-ref
     event-channel -> evt-event-channel
 * have 2 separate sections for req/resp and evt transport
   parameters
 * fix and extend recovery flow description
 * reserve request codes for future fbif integration if need be
   (request codes [0; 15] are reserved)
 * error on attempt to create multiple buffers with same cookie(s)
 * clarification of page directory usage for be_alloc feature
 * add editor's block

Changes since v2:
 * updated XenStore configuration template/pattern
 * added "Recovery flow" to state diagram description
 * renamed gref_directory_start to gref_directory
 * added missing "versions" and "version" string constants

Changes since v1:
 * fixed xendispl_event_page padding size
 * added versioning support
 * explicitly define value types for XenStore fields
 * text decoration re-work
 * added offsets to ASCII box notation

Changes since initial:
 * DRM changed to DISPL, protocol made generic
 * major re-work addressing issues raised for sndif

Signed-off-by: Oleksandr Grytsov <oleksandr_grytsov@epam.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 xen/include/public/io/displif.h | 847 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 847 insertions(+)
 create mode 100644 xen/include/public/io/displif.h

diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
new file mode 100644
index 000000000000..ac55c4fe8bbe
--- /dev/null
+++ b/xen/include/public/io/displif.h
@@ -0,0 +1,847 @@
+/******************************************************************************
+ * displif.h
+ *
+ * Unified display device I/O interface for Xen guest OSes.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ *
+ * Copyright (C) 2016-2017 EPAM Systems Inc.
+ *
+ * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
+ */
+
+#ifndef __XEN_PUBLIC_IO_DISPLIF_H__
+#define __XEN_PUBLIC_IO_DISPLIF_H__
+
+#include "ring.h"
+#include "../grant_table.h"
+
+/*
+ ******************************************************************************
+ *                  Main features provided by the protocol
+ ******************************************************************************
+ * This protocol aims to provide a unified protocol which fits more
+ * sophisticated use-cases than a framebuffer device can handle. At the
+ * moment basic functionality is supported with the intention to be extended:
+ *  o multiple dynamically allocated/destroyed framebuffers
+ *  o buffers of arbitrary sizes
+ *  o buffer allocation at either back or front end
+ *  o better configuration options including multiple display support
+ *
+ * Note: existing fbif can be used together with displif running at the
+ * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
+ *
+ * Note: display resolution (XenStore's "resolution" property) defines
+ * visible area of the virtual display. At the same time resolution of
+ * the display and frame buffers may differ: buffers can be smaller, equal
+ * or bigger than the visible area. This is to enable use-cases, where backend
+ * may do some post-processing of the display and frame buffers supplied,
+ * e.g. those buffers can be just a part of the final composition.
+ *
+ ******************************************************************************
+ *                        Direction of improvements
+ ******************************************************************************
+ * Future extensions to the existing protocol may include:
+ *  o display/connector cloning
+ *  o allocation of objects other than display buffers
+ *  o plane/overlay support
+ *  o scaling support
+ *  o rotation support
+ *
+ ******************************************************************************
+ *                  Feature and Parameter Negotiation
+ ******************************************************************************
+ *
+ * Front->back notifications: when enqueuing a new request, sending a
+ * notification can be made conditional on xendispl_req (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Backends must set
+ * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
+ *
+ * Back->front notifications: when enqueuing a new response, sending a
+ * notification can be made conditional on xendispl_resp (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Frontends must set
+ * xendispl_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
+ *
+ * The two halves of a para-virtual display driver utilize nodes within
+ * XenStore to communicate capabilities and to negotiate operating parameters.
+ * This section enumerates these nodes which reside in the respective front and
+ * backend portions of XenStore, following the XenBus convention.
+ *
+ * All data in XenStore is stored as strings. Nodes specifying numeric
+ * values are encoded in decimal. Integer value ranges listed below are
+ * expressed as fixed sized integer types capable of storing the conversion
+ * of a properly formated node string, without loss of information.
+ *
+ ******************************************************************************
+ *                        Example configuration
+ ******************************************************************************
+ *
+ * Note: depending on the use-case backend can expose more display connectors
+ * than the underlying HW physically has by employing SW graphics compositors
+ *
+ * This is an example of backend and frontend configuration:
+ *
+ *--------------------------------- Backend -----------------------------------
+ *
+ * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
+ * /local/domain/0/backend/vdispl/1/0/frontend = "/local/domain/1/device/vdispl/0"
+ * /local/domain/0/backend/vdispl/1/0/state = "4"
+ * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
+ *
+ *--------------------------------- Frontend ----------------------------------
+ *
+ * /local/domain/1/device/vdispl/0/backend-id = "0"
+ * /local/domain/1/device/vdispl/0/backend = "/local/domain/0/backend/vdispl/1/0"
+ * /local/domain/1/device/vdispl/0/state = "4"
+ * /local/domain/1/device/vdispl/0/version = "1"
+ * /local/domain/1/device/vdispl/0/be_alloc = "1"
+ *
+ *-------------------------- Connector 0 configuration ------------------------
+ *
+ * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
+ * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
+ * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
+ * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
+ * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
+ *
+ *-------------------------- Connector 1 configuration ------------------------
+ *
+ * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
+ * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
+ * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
+ * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
+ * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
+ *
+ ******************************************************************************
+ *                            Backend XenBus Nodes
+ ******************************************************************************
+ *
+ *----------------------------- Protocol version ------------------------------
+ *
+ * versions
+ *      Values:         <string>
+ *
+ *      List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
+ *      by the backend. For example "1,2,3".
+ *
+ ******************************************************************************
+ *                            Frontend XenBus Nodes
+ ******************************************************************************
+ *
+ *-------------------------------- Addressing ---------------------------------
+ *
+ * dom-id
+ *      Values:         <uint16_t>
+ *
+ *      Domain identifier.
+ *
+ * dev-id
+ *      Values:         <uint16_t>
+ *
+ *      Device identifier.
+ *
+ * conn-idx
+ *      Values:         <uint8_t>
+ *
+ *      Zero based contigous index of the connector.
+ *      /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
+ *
+ *----------------------------- Protocol version ------------------------------
+ *
+ * version
+ *      Values:         <string>
+ *
+ *      Protocol version, chosen among the ones supported by the backend.
+ *
+ *------------------------- Backend buffer allocation -------------------------
+ *
+ * be_alloc
+ *      Values:         "0", "1"
+ *
+ *      If value is set to "1", then backend can be a buffer provider/allocator
+ *      for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
+ *      for negotiation).
+ *      If value is not "1" or omitted frontend must allocate buffers itself.
+ *
+ *----------------------------- Connector settings ----------------------------
+ *
+ * resolution
+ *      Values:         <width, uint32_t>x<height, uint32_t>
+ *
+ *      Width and height of the connector in pixels separated by
+ *      XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
+ *      display.
+ *
+ *------------------ Connector Request Transport Parameters -------------------
+ *
+ * This communication path is used to deliver requests from frontend to backend
+ * and get the corresponding responses from backend to frontend,
+ * set up per connector.
+ *
+ * req-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen connector's control event channel
+ *      used to signal activity in the ring buffer.
+ *
+ * req-ring-ref
+ *      Values:         <uint32_t>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page in a single page sized connector's control ring buffer.
+ *
+ *------------------- Connector Event Transport Parameters --------------------
+ *
+ * This communication path is used to deliver asynchronous events from backend
+ * to frontend, set up per connector.
+ *
+ * evt-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen connector's event channel
+ *      used to signal activity in the ring buffer.
+ *
+ * evt-ring-ref
+ *      Values:         <uint32_t>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page in a single page sized connector's event ring buffer.
+ */
+
+/*
+ ******************************************************************************
+ *                               STATE DIAGRAMS
+ ******************************************************************************
+ *
+ * Tool stack creates front and back state nodes with initial state
+ * XenbusStateInitialising.
+ * Tool stack creates and sets up frontend display configuration
+ * nodes per domain.
+ *
+ *-------------------------------- Normal flow --------------------------------
+ *
+ * Front                                Back
+ * =================================    =====================================
+ * XenbusStateInitialising              XenbusStateInitialising
+ *                                       o Query backend device identification
+ *                                         data.
+ *                                       o Open and validate backend device.
+ *                                                |
+ *                                                |
+ *                                                V
+ *                                      XenbusStateInitWait
+ *
+ * o Query frontend configuration
+ * o Allocate and initialize
+ *   event channels per configured
+ *   connector.
+ * o Publish transport parameters
+ *   that will be in effect during
+ *   this connection.
+ *              |
+ *              |
+ *              V
+ * XenbusStateInitialised
+ *
+ *                                       o Query frontend transport parameters.
+ *                                       o Connect to the event channels.
+ *                                                |
+ *                                                |
+ *                                                V
+ *                                      XenbusStateConnected
+ *
+ *  o Create and initialize OS
+ *    virtual display connectors
+ *    as per configuration.
+ *              |
+ *              |
+ *              V
+ * XenbusStateConnected
+ *
+ *                                      XenbusStateUnknown
+ *                                      XenbusStateClosed
+ *                                      XenbusStateClosing
+ * o Remove virtual display device
+ * o Remove event channels
+ *              |
+ *              |
+ *              V
+ * XenbusStateClosed
+ *
+ *------------------------------- Recovery flow -------------------------------
+ *
+ * In case of frontend unrecoverable errors backend handles that as
+ * if frontend goes into the XenbusStateClosed state.
+ *
+ * In case of backend unrecoverable errors frontend tries removing
+ * the virtualized device. If this is possible at the moment of error,
+ * then frontend goes into the XenbusStateInitialising state and is ready for
+ * new connection with backend. If the virtualized device is still in use and
+ * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
+ * until either the virtualized device removed or backend initiates a new
+ * connection. On the virtualized device removal frontend goes into the
+ * XenbusStateInitialising state.
+ *
+ * Note on XenbusStateReconfiguring state of the frontend: if backend has
+ * unrecoverable errors then frontend cannot send requests to the backend
+ * and thus cannot provide functionality of the virtualized device anymore.
+ * After backend is back to normal the virtualized device may still hold some
+ * state: configuration in use, allocated buffers, client application state etc.
+ * So, in most cases, this will require frontend to implement complex recovery
+ * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
+ * frontend will make sure no new clients of the virtualized device are
+ * accepted, allow existing client(s) to exit gracefully by signaling error
+ * state etc.
+ * Once all the clients are gone frontend can reinitialize the virtualized
+ * device and get into XenbusStateInitialising state again signaling the
+ * backend that a new connection can be made.
+ *
+ * There are multiple conditions possible under which frontend will go from
+ * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
+ * specific. For example:
+ * 1. The underlying OS framework may provide callbacks to signal that the last
+ *    client of the virtualized device has gone and the device can be removed
+ * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
+ *    to periodically check if this is the right time to re-try removal of
+ *    the virtualized device.
+ * 3. By any other means.
+ *
+ ******************************************************************************
+ *                             REQUEST CODES
+ ******************************************************************************
+ * Request codes [0; 15] are reserved and must not be used
+ */
+
+#define XENDISPL_OP_DBUF_CREATE       0x10
+#define XENDISPL_OP_DBUF_DESTROY      0x11
+#define XENDISPL_OP_FB_ATTACH         0x12
+#define XENDISPL_OP_FB_DETACH         0x13
+#define XENDISPL_OP_SET_CONFIG        0x14
+#define XENDISPL_OP_PG_FLIP           0x15
+
+/*
+ ******************************************************************************
+ *                                 EVENT CODES
+ ******************************************************************************
+ */
+#define XENDISPL_EVT_PG_FLIP          0x00
+
+/*
+ ******************************************************************************
+ *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
+ ******************************************************************************
+ */
+#define XENDISPL_DRIVER_NAME          "vdispl"
+
+#define XENDISPL_LIST_SEPARATOR       ","
+#define XENDISPL_RESOLUTION_SEPARATOR "x"
+
+#define XENDISPL_FIELD_BE_VERSIONS    "versions"
+#define XENDISPL_FIELD_FE_VERSION     "version"
+#define XENDISPL_FIELD_REQ_RING_REF   "req-ring-ref"
+#define XENDISPL_FIELD_REQ_CHANNEL    "req-event-channel"
+#define XENDISPL_FIELD_EVT_RING_REF   "evt-ring-ref"
+#define XENDISPL_FIELD_EVT_CHANNEL    "evt-event-channel"
+#define XENDISPL_FIELD_RESOLUTION     "resolution"
+#define XENDISPL_FIELD_BE_ALLOC       "be_alloc"
+
+/*
+ ******************************************************************************
+ *                          STATUS RETURN CODES
+ ******************************************************************************
+ *
+ * Status return code is zero on success and -XEN_EXX on failure.
+ *
+ ******************************************************************************
+ *                              Assumptions
+ ******************************************************************************
+ * o usage of grant reference 0 as invalid grant reference:
+ *   grant reference 0 is valid, but never exposed to a PV driver,
+ *   because of the fact it is already in use/reserved by the PV console.
+ * o all references in this document to page sizes must be treated
+ *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
+ *
+ ******************************************************************************
+ *       Description of the protocol between frontend and backend driver
+ ******************************************************************************
+ *
+ * The two halves of a Para-virtual display driver communicate with
+ * each other using shared pages and event channels.
+ * Shared page contains a ring with request/response packets.
+ *
+ * All reserved fields in the structures below must be 0.
+ * Display buffers's cookie of value 0 treated as invalid.
+ * Framebuffer's cookie of value 0 treated as invalid.
+ *
+ * For all request/response/event packets that use cookies:
+ *   dbuf_cookie - uint64_t, unique to guest domain value used by the backend
+ *     to map remote display buffer to its local one
+ *   fb_cookie - uint64_t, unique to guest domain value used by the backend
+ *     to map remote framebuffer to its local one
+ *
+ *---------------------------------- Requests ---------------------------------
+ *
+ * All requests/responses, which are not connector specific, must be sent over
+ * control ring of the connector with index 0.
+ *
+ * All request packets have the same length (64 octets)
+ * All request packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ *   id - uint16_t, private guest value, echoed in response
+ *   operation - uint8_t, operation code, XENDISPL_OP_???
+ *
+ * Request dbuf creation - request creation of a display buffer.
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_DBUF_CREATE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie low 32-bit                      | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie high 32-bit                     | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                                bpp                                | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             buffer_sz                             | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                               flags                               | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                           gref_directory                          | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 44
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Must be sent over control ring of the connector with index 0.
+ * All unused bits in flags field must be set to 0.
+ *
+ * An attempt to create multiple display buffers with the same dbuf_cookie is
+ * an error. dbuf_cookie can be re-used after destroying the corresponding
+ * display buffer.
+ *
+ * Width and height of the display buffers can be smaller, equal or bigger
+ * than the connector's resolution. Depth/pixel format of the individual
+ * buffers can differ as well.
+ *
+ * width - uint32_t, width in pixels
+ * height - uint32_t, height in pixels
+ * bpp - uint32_t, bits per pixel
+ * buffer_sz - uint32_t, buffer size to be allocated, octets
+ * flags - uint32_t, flags of the operation
+ *   o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
+ *     to allocate the buffer with the parameters provided in this request.
+ *     Page directory is handled as follows:
+ *       Frontend on request:
+ *         o allocates pages for the directory (gref_directory,
+ *           gref_dir_next_page(s)
+ *         o grants permissions for the pages of the directory
+ *         o sets gref_dir_next_page fields
+ *       Backend on response:
+ *         o grants permissions for the pages of the buffer allocated
+ *         o fills in page directory with grant references
+ *           (gref[] in struct xendispl_page_directorygref)
+ * gref_directory - grant_ref_t, a reference to the first shared page
+ *   describing shared buffer references. At least one page exists. If shared
+ *   buffer size (buffer_sz) exceeds what can be addressed by this single page,
+ *   then reference to the next page must be supplied (see gref_dir_next_page
+ *   below)
+ */
+
+#define XENDISPL_DBUF_FLG_REQ_ALLOC       (1 << 0)
+
+struct xendispl_dbuf_create_req {
+    uint64_t dbuf_cookie;
+    uint32_t width;
+    uint32_t height;
+    uint32_t bpp;
+    uint32_t buffer_sz;
+    uint32_t flags;
+    grant_ref_t gref_directory;
+};
+
+/*
+ * Shared page for XENDISPL_OP_DBUF_CREATE buffer descriptor (gref_directory in
+ * the request) employs a list of pages, describing all pages of the shared
+ * data buffer:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |                        gref_dir_next_page                         | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              gref[0]                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                              gref[i]                              | i*4+8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             gref[N - 1]                           | N*4+8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * gref_dir_next_page - grant_ref_t, reference to the next page describing
+ *   page directory. Must be 0 if there are no more pages in the list.
+ * gref[i] - grant_ref_t, reference to a shared page of the buffer
+ *   allocated at XENDISPL_OP_DBUF_CREATE
+ *
+ * Number of grant_ref_t entries in the whole page directory is not
+ * passed, but instead can be calculated as:
+ *   num_grefs_total = (XENDISPL_OP_DBUF_CREATE.buffer_sz + XEN_PAGE_SIZE - 1) /
+ *       XEN_PAGE_SIZE
+ */
+
+struct xendispl_page_directory {
+    grant_ref_t gref_dir_next_page;
+    grant_ref_t gref[1]; /* Variable length */
+};
+
+/*
+ * Request dbuf destruction - destroy a previously allocated display buffer:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_DBUF_DESTROY|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie low 32-bit                      | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie high 32-bit                     | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Must be sent over control ring of the connector with index 0.
+ */
+
+struct xendispl_dbuf_destroy_req {
+    uint64_t dbuf_cookie;
+};
+
+/*
+ * Request framebuffer attachment - request attachment of a framebuffer to
+ * previously created display buffer.
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_FB_ATTACH  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie low 32-bit                      | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                       dbuf_cookie high 32-bit                     | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie low 32-bit                       | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie high 32-bit                      | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                            pixel_format                           | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 40
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Must be sent over control ring of the connector with index 0.
+ * Width and height can be smaller, equal or bigger than the connector's
+ * resolution.
+ *
+ * An attempt to create multiple frame buffers with the same fb_cookie is
+ * an error. fb_cookie can be re-used after destroying the corresponding
+ * frame buffer.
+ *
+ * width - uint32_t, width in pixels
+ * height - uint32_t, height in pixels
+ * pixel_format - uint32_t, pixel format of the framebuffer, FOURCC code
+ */
+
+struct xendispl_fb_attach_req {
+    uint64_t dbuf_cookie;
+    uint64_t fb_cookie;
+    uint32_t width;
+    uint32_t height;
+    uint32_t pixel_format;
+};
+
+/*
+ * Request framebuffer detach - detach a previously
+ * attached framebuffer from the display buffer in request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |  _OP_FB_DETACH |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Must be sent over control ring of the connector with index 0.
+ */
+
+struct xendispl_fb_detach_req {
+    uint64_t fb_cookie;
+};
+
+/*
+ * Request configuration set/reset - request to set or reset
+ * the configuration/mode of the display:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_SET_CONFIG |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                                 x                                 | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                                 y                                 | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                                bpp                                | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 44
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Pass all zeros to reset, otherwise command is treated as
+ * configuration set.
+ * Framebuffer's cookie defines which framebuffer/dbuf must be
+ * displayed while enabling display (applying configuration).
+ * x, y, width and height are bound by the connector's resolution and must not
+ * exceed it.
+ *
+ * x - uint32_t, starting position in pixels by X axis
+ * y - uint32_t, starting position in pixels by Y axis
+ * width - uint32_t, width in pixels
+ * height - uint32_t, height in pixels
+ * bpp - uint32_t, bits per pixel
+ */
+
+struct xendispl_set_config_req {
+    uint64_t fb_cookie;
+    uint32_t x;
+    uint32_t y;
+    uint32_t width;
+    uint32_t height;
+    uint32_t bpp;
+};
+
+/*
+ * Request page flip - request to flip a page identified by the framebuffer
+ * cookie:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_PG_FLIP    |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ */
+
+struct xendispl_page_flip_req {
+    uint64_t fb_cookie;
+};
+
+/*
+ *---------------------------------- Responses --------------------------------
+ *
+ * All response packets have the same length (64 octets)
+ *
+ * All response packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |            reserved             | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, private guest value, echoed from request
+ * status - int32_t, response status, zero on success and -XEN_EXX on failure
+ *
+ *----------------------------------- Events ----------------------------------
+ *
+ * Events are sent via a shared page allocated by the front and propagated by
+ *   evt-event-channel/evt-ring-ref XenStore entries
+ * All event packets have the same length (64 octets)
+ * All event packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |      type      |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, event id, may be used by front
+ * type - uint8_t, type of the event
+ *
+ *
+ * Page flip complete event - event from back to front on page flip completed:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |   _EVT_PG_FLIP |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                        fb_cookie high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ */
+
+struct xendispl_pg_flip_evt {
+    uint64_t fb_cookie;
+};
+
+struct xendispl_req {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved[5];
+    union {
+        struct xendispl_dbuf_create_req dbuf_create;
+        struct xendispl_dbuf_destroy_req dbuf_destroy;
+        struct xendispl_fb_attach_req fb_attach;
+        struct xendispl_fb_detach_req fb_detach;
+        struct xendispl_set_config_req set_config;
+        struct xendispl_page_flip_req pg_flip;
+        uint8_t reserved[56];
+    } op;
+};
+
+struct xendispl_resp {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved;
+    int32_t status;
+    uint8_t reserved1[56];
+};
+
+struct xendispl_evt {
+    uint16_t id;
+    uint8_t type;
+    uint8_t reserved[5];
+    union {
+        struct xendispl_pg_flip_evt pg_flip;
+        uint8_t reserved[56];
+    } op;
+};
+
+DEFINE_RING_TYPES(xen_displif, struct xendispl_req, struct xendispl_resp);
+
+/*
+ ******************************************************************************
+ *                        Back to front events delivery
+ ******************************************************************************
+ * In order to deliver asynchronous events from back to front a shared page is
+ * allocated by front and its granted reference propagated to back via
+ * XenStore entries (event-XXX).
+ * This page has a common header used by both front and back to synchronize
+ * access and control event's ring buffer, while back being a producer of the
+ * events and front being a consumer. The rest of the page after the header
+ * is used for event packets.
+ *
+ * Upon reception of an event(s) front may confirm its reception
+ * for either each event, group of events or none.
+ */
+
+struct xendispl_event_page {
+    uint32_t in_cons;
+    uint32_t in_prod;
+    uint8_t reserved[56];
+};
+
+#define XENDISPL_EVENT_PAGE_SIZE 4096
+#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
+#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - XENDISPL_IN_RING_OFFS)
+#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct xendispl_evt))
+#define XENDISPL_IN_RING(page) \
+	((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
+#define XENDISPL_IN_RING_REF(page, idx) \
+	(XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
+
+#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
2.7.4


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Re: [PATCH v4] displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

ping


On 03/20/2017 10:56 AM, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>
> This is the ABI for the two halves of a para-virtualized
> display driver.
>
> This protocol aims to provide a unified protocol which fits more
> sophisticated use-cases than a framebuffer device can handle. At the
> moment basic functionality is supported with the intention to extend:
>    o multiple dynamically allocated/destroyed framebuffers
>    o buffers of arbitrary sizes
>    o better configuration options including multiple display support
>
> Note: existing fbif can be used together with displif running at the
> same time, e.g. on Linux one provides framebuffer and another DRM/KMS
>
> Future extensions to the existing protocol may include:
>    o allow display/connector cloning
>    o allow allocating objects other than display buffers
>    o add planes/overlays support
>    o support scaling
>    o support rotation
>
> Note, that this protocol doesn't use ring macros for
> bi-directional exchange (PV calls/9pfs) bacause:
>    o it statically defines the use of a single page
>      for the ring buffer
>    o it uses direct memory access to ring's contents
>      w/o memory copying
>    o re-uses the same idea that kbdif/fbif use
>      which for this use-case seems to be appropriate
>
> ==================================================
> Rationale for introducing this protocol instead of
> using the existing fbif:
> ==================================================
>
> 1. In/out event sizes
>    o fbif - 40 octets
>    o displif - 40 octets
> This is only the initial version of the displif protocol
> which means that there could be requests which will not fit
> (WRT introducing some GPU related functionality
> later on). In that case we cannot alter fbif sizes as we need to
> be backward compatible an will be forced to handle those
> apart of fbif.
>
> 2. Shared page
> Displif doesn't use anything like struct xenfb_page, but
> DEFINE_RING_TYPES(xen_displif, struct xendispl_req, struct
> xendispl_resp) which is a better and more common way.
> Output events use a shared page which only has in_cons and in_prod
> and all the rest is used for incoming events. Here struct xenfb_page
> could probably be used as is despite the fact that it only has a half
> of a page for incoming events which is only 50 events. (consider
> something like 60Hz display)
>
> 3. Amount of changes.
> fbif only provides XENFB_TYPE_UPDATE and XENFB_TYPE_RESIZE
> events, so it looks like it is easier to get fb support into displif
> than vice versa. displif at the moment has 6 requests and 1 event,
> multiple connector support, etc.
>
> ---
> Changes since v3:
>   * add clarification on buffer's size/depth/format and
>     connector's resolution
>   * move be_alloc feature into domain's configuration
>     to allow more use-cases and freedom (e.g. for 1:1
>     mapped domains there may be no need to request backend
>     to allocate buffers, while for the rest it may make more
>     sense)
>   * rename XenStore entries:
>       ctrl-ring-ref -> req-ring-ref
>       ctrl-channel -> req-event-channel
>       event-ring-ref -> evt-ring-ref
>       event-channel -> evt-event-channel
>   * have 2 separate sections for req/resp and evt transport
>     parameters
>   * fix and extend recovery flow description
>   * reserve request codes for future fbif integration if need be
>     (request codes [0; 15] are reserved)
>   * error on attempt to create multiple buffers with same cookie(s)
>   * clarification of page directory usage for be_alloc feature
>   * add editor's block
>
> Changes since v2:
>   * updated XenStore configuration template/pattern
>   * added "Recovery flow" to state diagram description
>   * renamed gref_directory_start to gref_directory
>   * added missing "versions" and "version" string constants
>
> Changes since v1:
>   * fixed xendispl_event_page padding size
>   * added versioning support
>   * explicitly define value types for XenStore fields
>   * text decoration re-work
>   * added offsets to ASCII box notation
>
> Changes since initial:
>   * DRM changed to DISPL, protocol made generic
>   * major re-work addressing issues raised for sndif
>
> Signed-off-by: Oleksandr Grytsov <oleksandr_grytsov@epam.com>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
>   xen/include/public/io/displif.h | 847 ++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 847 insertions(+)
>   create mode 100644 xen/include/public/io/displif.h
>
> diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
> new file mode 100644
> index 000000000000..ac55c4fe8bbe
> --- /dev/null
> +++ b/xen/include/public/io/displif.h
> @@ -0,0 +1,847 @@
> +/******************************************************************************
> + * displif.h
> + *
> + * Unified display device I/O interface for Xen guest OSes.
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this software and associated documentation files (the "Software"), to
> + * deal in the Software without restriction, including without limitation the
> + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
> + * sell copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> + * DEALINGS IN THE SOFTWARE.
> + *
> + * Copyright (C) 2016-2017 EPAM Systems Inc.
> + *
> + * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> + *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
> + */
> +
> +#ifndef __XEN_PUBLIC_IO_DISPLIF_H__
> +#define __XEN_PUBLIC_IO_DISPLIF_H__
> +
> +#include "ring.h"
> +#include "../grant_table.h"
> +
> +/*
> + ******************************************************************************
> + *                  Main features provided by the protocol
> + ******************************************************************************
> + * This protocol aims to provide a unified protocol which fits more
> + * sophisticated use-cases than a framebuffer device can handle. At the
> + * moment basic functionality is supported with the intention to be extended:
> + *  o multiple dynamically allocated/destroyed framebuffers
> + *  o buffers of arbitrary sizes
> + *  o buffer allocation at either back or front end
> + *  o better configuration options including multiple display support
> + *
> + * Note: existing fbif can be used together with displif running at the
> + * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
> + *
> + * Note: display resolution (XenStore's "resolution" property) defines
> + * visible area of the virtual display. At the same time resolution of
> + * the display and frame buffers may differ: buffers can be smaller, equal
> + * or bigger than the visible area. This is to enable use-cases, where backend
> + * may do some post-processing of the display and frame buffers supplied,
> + * e.g. those buffers can be just a part of the final composition.
> + *
> + ******************************************************************************
> + *                        Direction of improvements
> + ******************************************************************************
> + * Future extensions to the existing protocol may include:
> + *  o display/connector cloning
> + *  o allocation of objects other than display buffers
> + *  o plane/overlay support
> + *  o scaling support
> + *  o rotation support
> + *
> + ******************************************************************************
> + *                  Feature and Parameter Negotiation
> + ******************************************************************************
> + *
> + * Front->back notifications: when enqueuing a new request, sending a
> + * notification can be made conditional on xendispl_req (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Backends must set
> + * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
> + *
> + * Back->front notifications: when enqueuing a new response, sending a
> + * notification can be made conditional on xendispl_resp (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Frontends must set
> + * xendispl_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
> + *
> + * The two halves of a para-virtual display driver utilize nodes within
> + * XenStore to communicate capabilities and to negotiate operating parameters.
> + * This section enumerates these nodes which reside in the respective front and
> + * backend portions of XenStore, following the XenBus convention.
> + *
> + * All data in XenStore is stored as strings. Nodes specifying numeric
> + * values are encoded in decimal. Integer value ranges listed below are
> + * expressed as fixed sized integer types capable of storing the conversion
> + * of a properly formated node string, without loss of information.
> + *
> + ******************************************************************************
> + *                        Example configuration
> + ******************************************************************************
> + *
> + * Note: depending on the use-case backend can expose more display connectors
> + * than the underlying HW physically has by employing SW graphics compositors
> + *
> + * This is an example of backend and frontend configuration:
> + *
> + *--------------------------------- Backend -----------------------------------
> + *
> + * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
> + * /local/domain/0/backend/vdispl/1/0/frontend = "/local/domain/1/device/vdispl/0"
> + * /local/domain/0/backend/vdispl/1/0/state = "4"
> + * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
> + *
> + *--------------------------------- Frontend ----------------------------------
> + *
> + * /local/domain/1/device/vdispl/0/backend-id = "0"
> + * /local/domain/1/device/vdispl/0/backend = "/local/domain/0/backend/vdispl/1/0"
> + * /local/domain/1/device/vdispl/0/state = "4"
> + * /local/domain/1/device/vdispl/0/version = "1"
> + * /local/domain/1/device/vdispl/0/be_alloc = "1"
> + *
> + *-------------------------- Connector 0 configuration ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
> + * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
> + * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
> + * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
> + * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
> + *
> + *-------------------------- Connector 1 configuration ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
> + * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
> + * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
> + * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
> + * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
> + *
> + ******************************************************************************
> + *                            Backend XenBus Nodes
> + ******************************************************************************
> + *
> + *----------------------------- Protocol version ------------------------------
> + *
> + * versions
> + *      Values:         <string>
> + *
> + *      List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
> + *      by the backend. For example "1,2,3".
> + *
> + ******************************************************************************
> + *                            Frontend XenBus Nodes
> + ******************************************************************************
> + *
> + *-------------------------------- Addressing ---------------------------------
> + *
> + * dom-id
> + *      Values:         <uint16_t>
> + *
> + *      Domain identifier.
> + *
> + * dev-id
> + *      Values:         <uint16_t>
> + *
> + *      Device identifier.
> + *
> + * conn-idx
> + *      Values:         <uint8_t>
> + *
> + *      Zero based contigous index of the connector.
> + *      /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
> + *
> + *----------------------------- Protocol version ------------------------------
> + *
> + * version
> + *      Values:         <string>
> + *
> + *      Protocol version, chosen among the ones supported by the backend.
> + *
> + *------------------------- Backend buffer allocation -------------------------
> + *
> + * be_alloc
> + *      Values:         "0", "1"
> + *
> + *      If value is set to "1", then backend can be a buffer provider/allocator
> + *      for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
> + *      for negotiation).
> + *      If value is not "1" or omitted frontend must allocate buffers itself.
> + *
> + *----------------------------- Connector settings ----------------------------
> + *
> + * resolution
> + *      Values:         <width, uint32_t>x<height, uint32_t>
> + *
> + *      Width and height of the connector in pixels separated by
> + *      XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
> + *      display.
> + *
> + *------------------ Connector Request Transport Parameters -------------------
> + *
> + * This communication path is used to deliver requests from frontend to backend
> + * and get the corresponding responses from backend to frontend,
> + * set up per connector.
> + *
> + * req-event-channel
> + *      Values:         <uint32_t>
> + *
> + *      The identifier of the Xen connector's control event channel
> + *      used to signal activity in the ring buffer.
> + *
> + * req-ring-ref
> + *      Values:         <uint32_t>
> + *
> + *      The Xen grant reference granting permission for the backend to map
> + *      a sole page in a single page sized connector's control ring buffer.
> + *
> + *------------------- Connector Event Transport Parameters --------------------
> + *
> + * This communication path is used to deliver asynchronous events from backend
> + * to frontend, set up per connector.
> + *
> + * evt-event-channel
> + *      Values:         <uint32_t>
> + *
> + *      The identifier of the Xen connector's event channel
> + *      used to signal activity in the ring buffer.
> + *
> + * evt-ring-ref
> + *      Values:         <uint32_t>
> + *
> + *      The Xen grant reference granting permission for the backend to map
> + *      a sole page in a single page sized connector's event ring buffer.
> + */
> +
> +/*
> + ******************************************************************************
> + *                               STATE DIAGRAMS
> + ******************************************************************************
> + *
> + * Tool stack creates front and back state nodes with initial state
> + * XenbusStateInitialising.
> + * Tool stack creates and sets up frontend display configuration
> + * nodes per domain.
> + *
> + *-------------------------------- Normal flow --------------------------------
> + *
> + * Front                                Back
> + * =================================    =====================================
> + * XenbusStateInitialising              XenbusStateInitialising
> + *                                       o Query backend device identification
> + *                                         data.
> + *                                       o Open and validate backend device.
> + *                                                |
> + *                                                |
> + *                                                V
> + *                                      XenbusStateInitWait
> + *
> + * o Query frontend configuration
> + * o Allocate and initialize
> + *   event channels per configured
> + *   connector.
> + * o Publish transport parameters
> + *   that will be in effect during
> + *   this connection.
> + *              |
> + *              |
> + *              V
> + * XenbusStateInitialised
> + *
> + *                                       o Query frontend transport parameters.
> + *                                       o Connect to the event channels.
> + *                                                |
> + *                                                |
> + *                                                V
> + *                                      XenbusStateConnected
> + *
> + *  o Create and initialize OS
> + *    virtual display connectors
> + *    as per configuration.
> + *              |
> + *              |
> + *              V
> + * XenbusStateConnected
> + *
> + *                                      XenbusStateUnknown
> + *                                      XenbusStateClosed
> + *                                      XenbusStateClosing
> + * o Remove virtual display device
> + * o Remove event channels
> + *              |
> + *              |
> + *              V
> + * XenbusStateClosed
> + *
> + *------------------------------- Recovery flow -------------------------------
> + *
> + * In case of frontend unrecoverable errors backend handles that as
> + * if frontend goes into the XenbusStateClosed state.
> + *
> + * In case of backend unrecoverable errors frontend tries removing
> + * the virtualized device. If this is possible at the moment of error,
> + * then frontend goes into the XenbusStateInitialising state and is ready for
> + * new connection with backend. If the virtualized device is still in use and
> + * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
> + * until either the virtualized device removed or backend initiates a new
> + * connection. On the virtualized device removal frontend goes into the
> + * XenbusStateInitialising state.
> + *
> + * Note on XenbusStateReconfiguring state of the frontend: if backend has
> + * unrecoverable errors then frontend cannot send requests to the backend
> + * and thus cannot provide functionality of the virtualized device anymore.
> + * After backend is back to normal the virtualized device may still hold some
> + * state: configuration in use, allocated buffers, client application state etc.
> + * So, in most cases, this will require frontend to implement complex recovery
> + * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
> + * frontend will make sure no new clients of the virtualized device are
> + * accepted, allow existing client(s) to exit gracefully by signaling error
> + * state etc.
> + * Once all the clients are gone frontend can reinitialize the virtualized
> + * device and get into XenbusStateInitialising state again signaling the
> + * backend that a new connection can be made.
> + *
> + * There are multiple conditions possible under which frontend will go from
> + * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
> + * specific. For example:
> + * 1. The underlying OS framework may provide callbacks to signal that the last
> + *    client of the virtualized device has gone and the device can be removed
> + * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
> + *    to periodically check if this is the right time to re-try removal of
> + *    the virtualized device.
> + * 3. By any other means.
> + *
> + ******************************************************************************
> + *                             REQUEST CODES
> + ******************************************************************************
> + * Request codes [0; 15] are reserved and must not be used
> + */
> +
> +#define XENDISPL_OP_DBUF_CREATE       0x10
> +#define XENDISPL_OP_DBUF_DESTROY      0x11
> +#define XENDISPL_OP_FB_ATTACH         0x12
> +#define XENDISPL_OP_FB_DETACH         0x13
> +#define XENDISPL_OP_SET_CONFIG        0x14
> +#define XENDISPL_OP_PG_FLIP           0x15
> +
> +/*
> + ******************************************************************************
> + *                                 EVENT CODES
> + ******************************************************************************
> + */
> +#define XENDISPL_EVT_PG_FLIP          0x00
> +
> +/*
> + ******************************************************************************
> + *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
> + ******************************************************************************
> + */
> +#define XENDISPL_DRIVER_NAME          "vdispl"
> +
> +#define XENDISPL_LIST_SEPARATOR       ","
> +#define XENDISPL_RESOLUTION_SEPARATOR "x"
> +
> +#define XENDISPL_FIELD_BE_VERSIONS    "versions"
> +#define XENDISPL_FIELD_FE_VERSION     "version"
> +#define XENDISPL_FIELD_REQ_RING_REF   "req-ring-ref"
> +#define XENDISPL_FIELD_REQ_CHANNEL    "req-event-channel"
> +#define XENDISPL_FIELD_EVT_RING_REF   "evt-ring-ref"
> +#define XENDISPL_FIELD_EVT_CHANNEL    "evt-event-channel"
> +#define XENDISPL_FIELD_RESOLUTION     "resolution"
> +#define XENDISPL_FIELD_BE_ALLOC       "be_alloc"
> +
> +/*
> + ******************************************************************************
> + *                          STATUS RETURN CODES
> + ******************************************************************************
> + *
> + * Status return code is zero on success and -XEN_EXX on failure.
> + *
> + ******************************************************************************
> + *                              Assumptions
> + ******************************************************************************
> + * o usage of grant reference 0 as invalid grant reference:
> + *   grant reference 0 is valid, but never exposed to a PV driver,
> + *   because of the fact it is already in use/reserved by the PV console.
> + * o all references in this document to page sizes must be treated
> + *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
> + *
> + ******************************************************************************
> + *       Description of the protocol between frontend and backend driver
> + ******************************************************************************
> + *
> + * The two halves of a Para-virtual display driver communicate with
> + * each other using shared pages and event channels.
> + * Shared page contains a ring with request/response packets.
> + *
> + * All reserved fields in the structures below must be 0.
> + * Display buffers's cookie of value 0 treated as invalid.
> + * Framebuffer's cookie of value 0 treated as invalid.
> + *
> + * For all request/response/event packets that use cookies:
> + *   dbuf_cookie - uint64_t, unique to guest domain value used by the backend
> + *     to map remote display buffer to its local one
> + *   fb_cookie - uint64_t, unique to guest domain value used by the backend
> + *     to map remote framebuffer to its local one
> + *
> + *---------------------------------- Requests ---------------------------------
> + *
> + * All requests/responses, which are not connector specific, must be sent over
> + * control ring of the connector with index 0.
> + *
> + * All request packets have the same length (64 octets)
> + * All request packets have common header:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |    operation   |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + *   id - uint16_t, private guest value, echoed in response
> + *   operation - uint8_t, operation code, XENDISPL_OP_???
> + *
> + * Request dbuf creation - request creation of a display buffer.
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |_OP_DBUF_CREATE |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie low 32-bit                      | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie high 32-bit                     | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                               width                               | 20
> + * +----------------+----------------+----------------+----------------+
> + * |                               height                              | 24
> + * +----------------+----------------+----------------+----------------+
> + * |                                bpp                                | 28
> + * +----------------+----------------+----------------+----------------+
> + * |                             buffer_sz                             | 32
> + * +----------------+----------------+----------------+----------------+
> + * |                               flags                               | 36
> + * +----------------+----------------+----------------+----------------+
> + * |                           gref_directory                          | 40
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 44
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + * All unused bits in flags field must be set to 0.
> + *
> + * An attempt to create multiple display buffers with the same dbuf_cookie is
> + * an error. dbuf_cookie can be re-used after destroying the corresponding
> + * display buffer.
> + *
> + * Width and height of the display buffers can be smaller, equal or bigger
> + * than the connector's resolution. Depth/pixel format of the individual
> + * buffers can differ as well.
> + *
> + * width - uint32_t, width in pixels
> + * height - uint32_t, height in pixels
> + * bpp - uint32_t, bits per pixel
> + * buffer_sz - uint32_t, buffer size to be allocated, octets
> + * flags - uint32_t, flags of the operation
> + *   o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
> + *     to allocate the buffer with the parameters provided in this request.
> + *     Page directory is handled as follows:
> + *       Frontend on request:
> + *         o allocates pages for the directory (gref_directory,
> + *           gref_dir_next_page(s)
> + *         o grants permissions for the pages of the directory
> + *         o sets gref_dir_next_page fields
> + *       Backend on response:
> + *         o grants permissions for the pages of the buffer allocated
> + *         o fills in page directory with grant references
> + *           (gref[] in struct xendispl_page_directorygref)
> + * gref_directory - grant_ref_t, a reference to the first shared page
> + *   describing shared buffer references. At least one page exists. If shared
> + *   buffer size (buffer_sz) exceeds what can be addressed by this single page,
> + *   then reference to the next page must be supplied (see gref_dir_next_page
> + *   below)
> + */
> +
> +#define XENDISPL_DBUF_FLG_REQ_ALLOC       (1 << 0)
> +
> +struct xendispl_dbuf_create_req {
> +    uint64_t dbuf_cookie;
> +    uint32_t width;
> +    uint32_t height;
> +    uint32_t bpp;
> +    uint32_t buffer_sz;
> +    uint32_t flags;
> +    grant_ref_t gref_directory;
> +};
> +
> +/*
> + * Shared page for XENDISPL_OP_DBUF_CREATE buffer descriptor (gref_directory in
> + * the request) employs a list of pages, describing all pages of the shared
> + * data buffer:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |                        gref_dir_next_page                         | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                              gref[0]                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                              gref[i]                              | i*4+8
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             gref[N - 1]                           | N*4+8
> + * +----------------+----------------+----------------+----------------+
> + *
> + * gref_dir_next_page - grant_ref_t, reference to the next page describing
> + *   page directory. Must be 0 if there are no more pages in the list.
> + * gref[i] - grant_ref_t, reference to a shared page of the buffer
> + *   allocated at XENDISPL_OP_DBUF_CREATE
> + *
> + * Number of grant_ref_t entries in the whole page directory is not
> + * passed, but instead can be calculated as:
> + *   num_grefs_total = (XENDISPL_OP_DBUF_CREATE.buffer_sz + XEN_PAGE_SIZE - 1) /
> + *       XEN_PAGE_SIZE
> + */
> +
> +struct xendispl_page_directory {
> +    grant_ref_t gref_dir_next_page;
> +    grant_ref_t gref[1]; /* Variable length */
> +};
> +
> +/*
> + * Request dbuf destruction - destroy a previously allocated display buffer:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |_OP_DBUF_DESTROY|   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie low 32-bit                      | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie high 32-bit                     | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 20
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + */
> +
> +struct xendispl_dbuf_destroy_req {
> +    uint64_t dbuf_cookie;
> +};
> +
> +/*
> + * Request framebuffer attachment - request attachment of a framebuffer to
> + * previously created display buffer.
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                | _OP_FB_ATTACH  |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie low 32-bit                      | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie high 32-bit                     | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie low 32-bit                       | 20
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie high 32-bit                      | 24
> + * +----------------+----------------+----------------+----------------+
> + * |                               width                               | 28
> + * +----------------+----------------+----------------+----------------+
> + * |                               height                              | 32
> + * +----------------+----------------+----------------+----------------+
> + * |                            pixel_format                           | 36
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 40
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + * Width and height can be smaller, equal or bigger than the connector's
> + * resolution.
> + *
> + * An attempt to create multiple frame buffers with the same fb_cookie is
> + * an error. fb_cookie can be re-used after destroying the corresponding
> + * frame buffer.
> + *
> + * width - uint32_t, width in pixels
> + * height - uint32_t, height in pixels
> + * pixel_format - uint32_t, pixel format of the framebuffer, FOURCC code
> + */
> +
> +struct xendispl_fb_attach_req {
> +    uint64_t dbuf_cookie;
> +    uint64_t fb_cookie;
> +    uint32_t width;
> +    uint32_t height;
> +    uint32_t pixel_format;
> +};
> +
> +/*
> + * Request framebuffer detach - detach a previously
> + * attached framebuffer from the display buffer in request:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |  _OP_FB_DETACH |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie low 32-bit                       | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie high 32-bit                      | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 20
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + */
> +
> +struct xendispl_fb_detach_req {
> +    uint64_t fb_cookie;
> +};
> +
> +/*
> + * Request configuration set/reset - request to set or reset
> + * the configuration/mode of the display:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                | _OP_SET_CONFIG |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie low 32-bit                       | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie high 32-bit                      | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                                 x                                 | 20
> + * +----------------+----------------+----------------+----------------+
> + * |                                 y                                 | 24
> + * +----------------+----------------+----------------+----------------+
> + * |                               width                               | 28
> + * +----------------+----------------+----------------+----------------+
> + * |                               height                              | 32
> + * +----------------+----------------+----------------+----------------+
> + * |                                bpp                                | 40
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 44
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Pass all zeros to reset, otherwise command is treated as
> + * configuration set.
> + * Framebuffer's cookie defines which framebuffer/dbuf must be
> + * displayed while enabling display (applying configuration).
> + * x, y, width and height are bound by the connector's resolution and must not
> + * exceed it.
> + *
> + * x - uint32_t, starting position in pixels by X axis
> + * y - uint32_t, starting position in pixels by Y axis
> + * width - uint32_t, width in pixels
> + * height - uint32_t, height in pixels
> + * bpp - uint32_t, bits per pixel
> + */
> +
> +struct xendispl_set_config_req {
> +    uint64_t fb_cookie;
> +    uint32_t x;
> +    uint32_t y;
> +    uint32_t width;
> +    uint32_t height;
> +    uint32_t bpp;
> +};
> +
> +/*
> + * Request page flip - request to flip a page identified by the framebuffer
> + * cookie:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                | _OP_PG_FLIP    |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie low 32-bit                       | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie high 32-bit                      | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 20
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + */
> +
> +struct xendispl_page_flip_req {
> +    uint64_t fb_cookie;
> +};
> +
> +/*
> + *---------------------------------- Responses --------------------------------
> + *
> + * All response packets have the same length (64 octets)
> + *
> + * All response packets have common header:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |            reserved             | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                              status                               | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 12
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * id - uint16_t, private guest value, echoed from request
> + * status - int32_t, response status, zero on success and -XEN_EXX on failure
> + *
> + *----------------------------------- Events ----------------------------------
> + *
> + * Events are sent via a shared page allocated by the front and propagated by
> + *   evt-event-channel/evt-ring-ref XenStore entries
> + * All event packets have the same length (64 octets)
> + * All event packets have common header:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |      type      |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + *
> + * id - uint16_t, event id, may be used by front
> + * type - uint8_t, type of the event
> + *
> + *
> + * Page flip complete event - event from back to front on page flip completed:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |   _EVT_PG_FLIP |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie low 32-bit                       | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                        fb_cookie high 32-bit                      | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 20
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + */
> +
> +struct xendispl_pg_flip_evt {
> +    uint64_t fb_cookie;
> +};
> +
> +struct xendispl_req {
> +    uint16_t id;
> +    uint8_t operation;
> +    uint8_t reserved[5];
> +    union {
> +        struct xendispl_dbuf_create_req dbuf_create;
> +        struct xendispl_dbuf_destroy_req dbuf_destroy;
> +        struct xendispl_fb_attach_req fb_attach;
> +        struct xendispl_fb_detach_req fb_detach;
> +        struct xendispl_set_config_req set_config;
> +        struct xendispl_page_flip_req pg_flip;
> +        uint8_t reserved[56];
> +    } op;
> +};
> +
> +struct xendispl_resp {
> +    uint16_t id;
> +    uint8_t operation;
> +    uint8_t reserved;
> +    int32_t status;
> +    uint8_t reserved1[56];
> +};
> +
> +struct xendispl_evt {
> +    uint16_t id;
> +    uint8_t type;
> +    uint8_t reserved[5];
> +    union {
> +        struct xendispl_pg_flip_evt pg_flip;
> +        uint8_t reserved[56];
> +    } op;
> +};
> +
> +DEFINE_RING_TYPES(xen_displif, struct xendispl_req, struct xendispl_resp);
> +
> +/*
> + ******************************************************************************
> + *                        Back to front events delivery
> + ******************************************************************************
> + * In order to deliver asynchronous events from back to front a shared page is
> + * allocated by front and its granted reference propagated to back via
> + * XenStore entries (event-XXX).
> + * This page has a common header used by both front and back to synchronize
> + * access and control event's ring buffer, while back being a producer of the
> + * events and front being a consumer. The rest of the page after the header
> + * is used for event packets.
> + *
> + * Upon reception of an event(s) front may confirm its reception
> + * for either each event, group of events or none.
> + */
> +
> +struct xendispl_event_page {
> +    uint32_t in_cons;
> +    uint32_t in_prod;
> +    uint8_t reserved[56];
> +};
> +
> +#define XENDISPL_EVENT_PAGE_SIZE 4096
> +#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
> +#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - XENDISPL_IN_RING_OFFS)
> +#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct xendispl_evt))
> +#define XENDISPL_IN_RING(page) \
> +	((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
> +#define XENDISPL_IN_RING_REF(page, idx) \
> +	(XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
> +
> +#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */


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Re: [PATCH v4] displif: add ABI for para-virtual display

[Konrad Rzeszutek Wilk]

Hey!

I only had minor comments - and if you are OK with them I can also
put them in the patch when checking them in (or if you want you can
repost it right away and I will check in the new version).

> 
> ---
> Changes since v3:
>  * add clarification on buffer's size/depth/format and
>    connector's resolution
>  * move be_alloc feature into domain's configuration
>    to allow more use-cases and freedom (e.g. for 1:1
>    mapped domains there may be no need to request backend
>    to allocate buffers, while for the rest it may make more
>    sense)
>  * rename XenStore entries:
>      ctrl-ring-ref -> req-ring-ref
>      ctrl-channel -> req-event-channel
>      event-ring-ref -> evt-ring-ref
>      event-channel -> evt-event-channel
>  * have 2 separate sections for req/resp and evt transport
>    parameters
>  * fix and extend recovery flow description
>  * reserve request codes for future fbif integration if need be
>    (request codes [0; 15] are reserved)
>  * error on attempt to create multiple buffers with same cookie(s)
>  * clarification of page directory usage for be_alloc feature
>  * add editor's block
> 
> Changes since v2:
>  * updated XenStore configuration template/pattern
>  * added "Recovery flow" to state diagram description
>  * renamed gref_directory_start to gref_directory
>  * added missing "versions" and "version" string constants
> 
> Changes since v1:
>  * fixed xendispl_event_page padding size
>  * added versioning support
>  * explicitly define value types for XenStore fields
>  * text decoration re-work
>  * added offsets to ASCII box notation
> 
> Changes since initial:
>  * DRM changed to DISPL, protocol made generic
>  * major re-work addressing issues raised for sndif
> 
> Signed-off-by: Oleksandr Grytsov <oleksandr_grytsov@epam.com>
> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> ---
>  xen/include/public/io/displif.h | 847 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 847 insertions(+)
>  create mode 100644 xen/include/public/io/displif.h
> 
> diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
> new file mode 100644
> index 000000000000..ac55c4fe8bbe
> --- /dev/null
> +++ b/xen/include/public/io/displif.h
> @@ -0,0 +1,847 @@
> +/******************************************************************************
> + * displif.h
> + *
> + * Unified display device I/O interface for Xen guest OSes.
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a copy
> + * of this software and associated documentation files (the "Software"), to
> + * deal in the Software without restriction, including without limitation the
> + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
> + * sell copies of the Software, and to permit persons to whom the Software is
> + * furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> + * DEALINGS IN THE SOFTWARE.
> + *
> + * Copyright (C) 2016-2017 EPAM Systems Inc.
> + *
> + * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
> + *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
> + */
> +
> +#ifndef __XEN_PUBLIC_IO_DISPLIF_H__
> +#define __XEN_PUBLIC_IO_DISPLIF_H__
> +
> +#include "ring.h"
> +#include "../grant_table.h"
> +
> +/*
> + ******************************************************************************
> + *                  Main features provided by the protocol
> + ******************************************************************************
> + * This protocol aims to provide a unified protocol which fits more
> + * sophisticated use-cases than a framebuffer device can handle. At the
> + * moment basic functionality is supported with the intention to be extended:
> + *  o multiple dynamically allocated/destroyed framebuffers
> + *  o buffers of arbitrary sizes
> + *  o buffer allocation at either back or front end
> + *  o better configuration options including multiple display support
> + *
> + * Note: existing fbif can be used together with displif running at the
> + * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
> + *
> + * Note: display resolution (XenStore's "resolution" property) defines
> + * visible area of the virtual display. At the same time resolution of
> + * the display and frame buffers may differ: buffers can be smaller, equal
> + * or bigger than the visible area. This is to enable use-cases, where backend
> + * may do some post-processing of the display and frame buffers supplied,
> + * e.g. those buffers can be just a part of the final composition.
> + *
> + ******************************************************************************
> + *                        Direction of improvements
> + ******************************************************************************
> + * Future extensions to the existing protocol may include:
> + *  o display/connector cloning
> + *  o allocation of objects other than display buffers
> + *  o plane/overlay support
> + *  o scaling support
> + *  o rotation support
> + *
> + ******************************************************************************
> + *                  Feature and Parameter Negotiation
> + ******************************************************************************
> + *
> + * Front->back notifications: when enqueuing a new request, sending a
> + * notification can be made conditional on xendispl_req (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Backends must set
> + * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
> + *
> + * Back->front notifications: when enqueuing a new response, sending a
> + * notification can be made conditional on xendispl_resp (i.e., the generic
> + * hold-off mechanism provided by the ring macros). Frontends must set
> + * xendispl_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
> + *
> + * The two halves of a para-virtual display driver utilize nodes within
> + * XenStore to communicate capabilities and to negotiate operating parameters.
> + * This section enumerates these nodes which reside in the respective front and
> + * backend portions of XenStore, following the XenBus convention.
> + *
> + * All data in XenStore is stored as strings. Nodes specifying numeric
> + * values are encoded in decimal. Integer value ranges listed below are
> + * expressed as fixed sized integer types capable of storing the conversion
> + * of a properly formated node string, without loss of information.
> + *
> + ******************************************************************************
> + *                        Example configuration
> + ******************************************************************************
> + *
> + * Note: depending on the use-case backend can expose more display connectors
> + * than the underlying HW physically has by employing SW graphics compositors
> + *
> + * This is an example of backend and frontend configuration:
> + *
> + *--------------------------------- Backend -----------------------------------
> + *
> + * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
> + * /local/domain/0/backend/vdispl/1/0/frontend = "/local/domain/1/device/vdispl/0"
> + * /local/domain/0/backend/vdispl/1/0/state = "4"
> + * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
> + *
> + *--------------------------------- Frontend ----------------------------------
> + *
> + * /local/domain/1/device/vdispl/0/backend-id = "0"
> + * /local/domain/1/device/vdispl/0/backend = "/local/domain/0/backend/vdispl/1/0"
> + * /local/domain/1/device/vdispl/0/state = "4"
> + * /local/domain/1/device/vdispl/0/version = "1"
> + * /local/domain/1/device/vdispl/0/be_alloc = "1"


This could be changed to '-'. As in "be-alloc" instead of "be_alloc"
> + *
> + *-------------------------- Connector 0 configuration ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
> + * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
> + * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
> + * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
> + * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
> + *
> + *-------------------------- Connector 1 configuration ------------------------
> + *
> + * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
> + * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
> + * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
> + * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
> + * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
> + *
> + ******************************************************************************
> + *                            Backend XenBus Nodes
> + ******************************************************************************
> + *
> + *----------------------------- Protocol version ------------------------------
> + *
> + * versions
> + *      Values:         <string>
> + *
> + *      List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
> + *      by the backend. For example "1,2,3".
> + *
> + ******************************************************************************
> + *                            Frontend XenBus Nodes
> + ******************************************************************************
> + *
> + *-------------------------------- Addressing ---------------------------------
> + *
> + * dom-id
> + *      Values:         <uint16_t>
> + *
> + *      Domain identifier.
> + *
> + * dev-id
> + *      Values:         <uint16_t>
> + *
> + *      Device identifier.
> + *
> + * conn-idx
> + *      Values:         <uint8_t>
> + *
> + *      Zero based contigous index of the connector.
> + *      /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
> + *
> + *----------------------------- Protocol version ------------------------------
> + *
> + * version
> + *      Values:         <string>
> + *
> + *      Protocol version, chosen among the ones supported by the backend.
> + *
> + *------------------------- Backend buffer allocation -------------------------
> + *
> + * be_alloc
> + *      Values:         "0", "1"
> + *
> + *      If value is set to "1", then backend can be a buffer provider/allocator
> + *      for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
> + *      for negotiation).
> + *      If value is not "1" or omitted frontend must allocate buffers itself.
> + *
> + *----------------------------- Connector settings ----------------------------
> + *
> + * resolution
> + *      Values:         <width, uint32_t>x<height, uint32_t>
> + *
> + *      Width and height of the connector in pixels separated by
> + *      XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
> + *      display.
> + *
> + *------------------ Connector Request Transport Parameters -------------------
> + *
> + * This communication path is used to deliver requests from frontend to backend
> + * and get the corresponding responses from backend to frontend,
> + * set up per connector.
> + *
> + * req-event-channel
> + *      Values:         <uint32_t>
> + *
> + *      The identifier of the Xen connector's control event channel
> + *      used to signal activity in the ring buffer.
> + *
> + * req-ring-ref
> + *      Values:         <uint32_t>
> + *
> + *      The Xen grant reference granting permission for the backend to map
> + *      a sole page in a single page sized connector's control ring buffer.

Perhaps s/in a single page sized/of/ ?


> + *
> + *------------------- Connector Event Transport Parameters --------------------
> + *
> + * This communication path is used to deliver asynchronous events from backend
> + * to frontend, set up per connector.
> + *
> + * evt-event-channel
> + *      Values:         <uint32_t>
> + *
> + *      The identifier of the Xen connector's event channel
> + *      used to signal activity in the ring buffer.
> + *
> + * evt-ring-ref
> + *      Values:         <uint32_t>
> + *
> + *      The Xen grant reference granting permission for the backend to map
> + *      a sole page in a single page sized connector's event ring buffer.

The same here? s/in a single page sized/of/
> + */
> +
> +/*
> + ******************************************************************************
> + *                               STATE DIAGRAMS
> + ******************************************************************************
> + *
> + * Tool stack creates front and back state nodes with initial state
> + * XenbusStateInitialising.
> + * Tool stack creates and sets up frontend display configuration
> + * nodes per domain.
> + *
> + *-------------------------------- Normal flow --------------------------------
> + *
> + * Front                                Back
> + * =================================    =====================================
> + * XenbusStateInitialising              XenbusStateInitialising
> + *                                       o Query backend device identification
> + *                                         data.
> + *                                       o Open and validate backend device.
> + *                                                |
> + *                                                |
> + *                                                V
> + *                                      XenbusStateInitWait
> + *
> + * o Query frontend configuration
> + * o Allocate and initialize
> + *   event channels per configured
> + *   connector.
> + * o Publish transport parameters
> + *   that will be in effect during
> + *   this connection.
> + *              |
> + *              |
> + *              V
> + * XenbusStateInitialised
> + *
> + *                                       o Query frontend transport parameters.
> + *                                       o Connect to the event channels.
> + *                                                |
> + *                                                |
> + *                                                V
> + *                                      XenbusStateConnected
> + *
> + *  o Create and initialize OS
> + *    virtual display connectors
> + *    as per configuration.
> + *              |
> + *              |
> + *              V
> + * XenbusStateConnected
> + *
> + *                                      XenbusStateUnknown
> + *                                      XenbusStateClosed
> + *                                      XenbusStateClosing
> + * o Remove virtual display device
> + * o Remove event channels
> + *              |
> + *              |
> + *              V
> + * XenbusStateClosed
> + *
> + *------------------------------- Recovery flow -------------------------------
> + *
> + * In case of frontend unrecoverable errors backend handles that as
> + * if frontend goes into the XenbusStateClosed state.
> + *
> + * In case of backend unrecoverable errors frontend tries removing
> + * the virtualized device. If this is possible at the moment of error,
> + * then frontend goes into the XenbusStateInitialising state and is ready for
> + * new connection with backend. If the virtualized device is still in use and
> + * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
> + * until either the virtualized device removed or backend initiates a new

s/removed/is removed/

> + * connection. On the virtualized device removal frontend goes into the
> + * XenbusStateInitialising state.
> + *
> + * Note on XenbusStateReconfiguring state of the frontend: if backend has
> + * unrecoverable errors then frontend cannot send requests to the backend
> + * and thus cannot provide functionality of the virtualized device anymore.
> + * After backend is back to normal the virtualized device may still hold some
> + * state: configuration in use, allocated buffers, client application state etc.
> + * So, in most cases, this will require frontend to implement complex recovery

s/So, in/In/
> + * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
> + * frontend will make sure no new clients of the virtualized device are
> + * accepted, allow existing client(s) to exit gracefully by signaling error
> + * state etc.
> + * Once all the clients are gone frontend can reinitialize the virtualized
> + * device and get into XenbusStateInitialising state again signaling the
> + * backend that a new connection can be made.
> + *
> + * There are multiple conditions possible under which frontend will go from
> + * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
> + * specific. For example:
> + * 1. The underlying OS framework may provide callbacks to signal that the last
> + *    client of the virtualized device has gone and the device can be removed
> + * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
> + *    to periodically check if this is the right time to re-try removal of
> + *    the virtualized device.
> + * 3. By any other means.
> + *
> + ******************************************************************************
> + *                             REQUEST CODES
> + ******************************************************************************
> + * Request codes [0; 15] are reserved and must not be used
> + */
> +
> +#define XENDISPL_OP_DBUF_CREATE       0x10
> +#define XENDISPL_OP_DBUF_DESTROY      0x11
> +#define XENDISPL_OP_FB_ATTACH         0x12
> +#define XENDISPL_OP_FB_DETACH         0x13
> +#define XENDISPL_OP_SET_CONFIG        0x14
> +#define XENDISPL_OP_PG_FLIP           0x15
> +
> +/*
> + ******************************************************************************
> + *                                 EVENT CODES
> + ******************************************************************************
> + */
> +#define XENDISPL_EVT_PG_FLIP          0x00
> +
> +/*
> + ******************************************************************************
> + *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
> + ******************************************************************************
> + */
> +#define XENDISPL_DRIVER_NAME          "vdispl"
> +
> +#define XENDISPL_LIST_SEPARATOR       ","
> +#define XENDISPL_RESOLUTION_SEPARATOR "x"
> +
> +#define XENDISPL_FIELD_BE_VERSIONS    "versions"
> +#define XENDISPL_FIELD_FE_VERSION     "version"
> +#define XENDISPL_FIELD_REQ_RING_REF   "req-ring-ref"
> +#define XENDISPL_FIELD_REQ_CHANNEL    "req-event-channel"
> +#define XENDISPL_FIELD_EVT_RING_REF   "evt-ring-ref"
> +#define XENDISPL_FIELD_EVT_CHANNEL    "evt-event-channel"
> +#define XENDISPL_FIELD_RESOLUTION     "resolution"
> +#define XENDISPL_FIELD_BE_ALLOC       "be_alloc"

s/be_alloc/be-alloc/ ?


> +
> +/*
> + ******************************************************************************
> + *                          STATUS RETURN CODES
> + ******************************************************************************
> + *
> + * Status return code is zero on success and -XEN_EXX on failure.
> + *
> + ******************************************************************************
> + *                              Assumptions
> + ******************************************************************************
> + * o usage of grant reference 0 as invalid grant reference:
> + *   grant reference 0 is valid, but never exposed to a PV driver,
> + *   because of the fact it is already in use/reserved by the PV console.
> + * o all references in this document to page sizes must be treated
> + *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
> + *
> + ******************************************************************************
> + *       Description of the protocol between frontend and backend driver
> + ******************************************************************************
> + *
> + * The two halves of a Para-virtual display driver communicate with
> + * each other using shared pages and event channels.
> + * Shared page contains a ring with request/response packets.
> + *
> + * All reserved fields in the structures below must be 0.
> + * Display buffers's cookie of value 0 treated as invalid.

s/treated/is treated/
> + * Framebuffer's cookie of value 0 treated as invalid.

s/treated/is treated/
> + *
> + * For all request/response/event packets that use cookies:
> + *   dbuf_cookie - uint64_t, unique to guest domain value used by the backend
> + *     to map remote display buffer to its local one
> + *   fb_cookie - uint64_t, unique to guest domain value used by the backend
> + *     to map remote framebuffer to its local one
> + *
> + *---------------------------------- Requests ---------------------------------
> + *
> + * All requests/responses, which are not connector specific, must be sent over
> + * control ring of the connector with index 0.

s/with index 0/which has the index value of 0/ ?

[and for the four other places]. The 'with index 0' got me thinking that the
structure has to have some index 0. But you mean that it should go over:

/local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref

Perhaps include that? Like:

"
control ring of the connector which has the index value of 0:
/local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref

"?

> + *
> + * All request packets have the same length (64 octets)
> + * All request packets have common header:
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |    operation   |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + *   id - uint16_t, private guest value, echoed in response
> + *   operation - uint8_t, operation code, XENDISPL_OP_???
> + *
> + * Request dbuf creation - request creation of a display buffer.
> + *         0                1                 2               3        octet
> + * +----------------+----------------+----------------+----------------+
> + * |               id                |_OP_DBUF_CREATE |   reserved     | 4
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 8
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie low 32-bit                      | 12
> + * +----------------+----------------+----------------+----------------+
> + * |                       dbuf_cookie high 32-bit                     | 16
> + * +----------------+----------------+----------------+----------------+
> + * |                               width                               | 20
> + * +----------------+----------------+----------------+----------------+
> + * |                               height                              | 24
> + * +----------------+----------------+----------------+----------------+
> + * |                                bpp                                | 28
> + * +----------------+----------------+----------------+----------------+
> + * |                             buffer_sz                             | 32
> + * +----------------+----------------+----------------+----------------+
> + * |                               flags                               | 36
> + * +----------------+----------------+----------------+----------------+
> + * |                           gref_directory                          | 40
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 44
> + * +----------------+----------------+----------------+----------------+
> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
> + * +----------------+----------------+----------------+----------------+
> + * |                             reserved                              | 64
> + * +----------------+----------------+----------------+----------------+
> + *
> + * Must be sent over control ring of the connector with index 0.
> + * All unused bits in flags field must be set to 0.
> + *
> + * An attempt to create multiple display buffers with the same dbuf_cookie is
> + * an error. dbuf_cookie can be re-used after destroying the corresponding
> + * display buffer.
> + *
> + * Width and height of the display buffers can be smaller, equal or bigger
> + * than the connector's resolution. Depth/pixel format of the individual
> + * buffers can differ as well.
> + *
> + * width - uint32_t, width in pixels
> + * height - uint32_t, height in pixels
> + * bpp - uint32_t, bits per pixel
> + * buffer_sz - uint32_t, buffer size to be allocated, octets
> + * flags - uint32_t, flags of the operation
> + *   o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
> + *     to allocate the buffer with the parameters provided in this request.
> + *     Page directory is handled as follows:
> + *       Frontend on request:
> + *         o allocates pages for the directory (gref_directory,
> + *           gref_dir_next_page(s)
> + *         o grants permissions for the pages of the directory

.. to the backend.
> + *         o sets gref_dir_next_page fields
> + *       Backend on response:
> + *         o grants permissions for the pages of the buffer allocated

.. to the frontend
> + *         o fills in page directory with grant references
> + *           (gref[] in struct xendispl_page_directorygref)

s/directorygref/xendispl_page_directory

> + * gref_directory - grant_ref_t, a reference to the first shared page
> + *   describing shared buffer references. At least one page exists. If shared
> + *   buffer size (buffer_sz) exceeds what can be addressed by this single page,
> + *   then reference to the next page must be supplied (see gref_dir_next_page
> + *   below)
> + */
> +

.. snip..
> + ******************************************************************************
> + *                        Back to front events delivery
> + ******************************************************************************
> + * In order to deliver asynchronous events from back to front a shared page is
> + * allocated by front and its granted reference propagated to back via
> + * XenStore entries (event-XXX).


s/event-XXXX/.. the right name?/

> + * This page has a common header used by both front and back to synchronize
> + * access and control event's ring buffer, while back being a producer of the
> + * events and front being a consumer. The rest of the page after the header
> + * is used for event packets.
> + *
> + * Upon reception of an event(s) front may confirm its reception
> + * for either each event, group of events or none.
> + */
> +
> +struct xendispl_event_page {
> +    uint32_t in_cons;
> +    uint32_t in_prod;
> +    uint8_t reserved[56];
> +};
> +
> +#define XENDISPL_EVENT_PAGE_SIZE 4096
> +#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
> +#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - XENDISPL_IN_RING_OFFS)
> +#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct xendispl_evt))
> +#define XENDISPL_IN_RING(page) \
> +	((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
> +#define XENDISPL_IN_RING_REF(page, idx) \
> +	(XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
> +
> +#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> -- 
> 2.7.4
> 

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Re: [PATCH v4] displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

Hi, Konrad!


On 04/04/2017 10:38 PM, Konrad Rzeszutek Wilk wrote:
> Hey!
>
> I only had minor comments - and if you are OK with them
comments seem to be reasonable to me
>   I can also
> put them in the patch when checking them in
Please, do me a favor
>   (or if you want you can
> repost it right away and I will check in the new version).
>
>> ---
>> Changes since v3:
>>   * add clarification on buffer's size/depth/format and
>>     connector's resolution
>>   * move be_alloc feature into domain's configuration
>>     to allow more use-cases and freedom (e.g. for 1:1
>>     mapped domains there may be no need to request backend
>>     to allocate buffers, while for the rest it may make more
>>     sense)
>>   * rename XenStore entries:
>>       ctrl-ring-ref -> req-ring-ref
>>       ctrl-channel -> req-event-channel
>>       event-ring-ref -> evt-ring-ref
>>       event-channel -> evt-event-channel
>>   * have 2 separate sections for req/resp and evt transport
>>     parameters
>>   * fix and extend recovery flow description
>>   * reserve request codes for future fbif integration if need be
>>     (request codes [0; 15] are reserved)
>>   * error on attempt to create multiple buffers with same cookie(s)
>>   * clarification of page directory usage for be_alloc feature
>>   * add editor's block
>>
>> Changes since v2:
>>   * updated XenStore configuration template/pattern
>>   * added "Recovery flow" to state diagram description
>>   * renamed gref_directory_start to gref_directory
>>   * added missing "versions" and "version" string constants
>>
>> Changes since v1:
>>   * fixed xendispl_event_page padding size
>>   * added versioning support
>>   * explicitly define value types for XenStore fields
>>   * text decoration re-work
>>   * added offsets to ASCII box notation
>>
>> Changes since initial:
>>   * DRM changed to DISPL, protocol made generic
>>   * major re-work addressing issues raised for sndif
>>
>> Signed-off-by: Oleksandr Grytsov <oleksandr_grytsov@epam.com>
>> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> ---
>>   xen/include/public/io/displif.h | 847 ++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 847 insertions(+)
>>   create mode 100644 xen/include/public/io/displif.h
>>
>> diff --git a/xen/include/public/io/displif.h b/xen/include/public/io/displif.h
>> new file mode 100644
>> index 000000000000..ac55c4fe8bbe
>> --- /dev/null
>> +++ b/xen/include/public/io/displif.h
>> @@ -0,0 +1,847 @@
>> +/******************************************************************************
>> + * displif.h
>> + *
>> + * Unified display device I/O interface for Xen guest OSes.
>> + *
>> + * Permission is hereby granted, free of charge, to any person obtaining a copy
>> + * of this software and associated documentation files (the "Software"), to
>> + * deal in the Software without restriction, including without limitation the
>> + * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
>> + * sell copies of the Software, and to permit persons to whom the Software is
>> + * furnished to do so, subject to the following conditions:
>> + *
>> + * The above copyright notice and this permission notice shall be included in
>> + * all copies or substantial portions of the Software.
>> + *
>> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
>> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
>> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
>> + * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
>> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
>> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
>> + * DEALINGS IN THE SOFTWARE.
>> + *
>> + * Copyright (C) 2016-2017 EPAM Systems Inc.
>> + *
>> + * Authors: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> + *          Oleksandr Grytsov <oleksandr_grytsov@epam.com>
>> + */
>> +
>> +#ifndef __XEN_PUBLIC_IO_DISPLIF_H__
>> +#define __XEN_PUBLIC_IO_DISPLIF_H__
>> +
>> +#include "ring.h"
>> +#include "../grant_table.h"
>> +
>> +/*
>> + ******************************************************************************
>> + *                  Main features provided by the protocol
>> + ******************************************************************************
>> + * This protocol aims to provide a unified protocol which fits more
>> + * sophisticated use-cases than a framebuffer device can handle. At the
>> + * moment basic functionality is supported with the intention to be extended:
>> + *  o multiple dynamically allocated/destroyed framebuffers
>> + *  o buffers of arbitrary sizes
>> + *  o buffer allocation at either back or front end
>> + *  o better configuration options including multiple display support
>> + *
>> + * Note: existing fbif can be used together with displif running at the
>> + * same time, e.g. on Linux one provides framebuffer and another DRM/KMS
>> + *
>> + * Note: display resolution (XenStore's "resolution" property) defines
>> + * visible area of the virtual display. At the same time resolution of
>> + * the display and frame buffers may differ: buffers can be smaller, equal
>> + * or bigger than the visible area. This is to enable use-cases, where backend
>> + * may do some post-processing of the display and frame buffers supplied,
>> + * e.g. those buffers can be just a part of the final composition.
>> + *
>> + ******************************************************************************
>> + *                        Direction of improvements
>> + ******************************************************************************
>> + * Future extensions to the existing protocol may include:
>> + *  o display/connector cloning
>> + *  o allocation of objects other than display buffers
>> + *  o plane/overlay support
>> + *  o scaling support
>> + *  o rotation support
>> + *
>> + ******************************************************************************
>> + *                  Feature and Parameter Negotiation
>> + ******************************************************************************
>> + *
>> + * Front->back notifications: when enqueuing a new request, sending a
>> + * notification can be made conditional on xendispl_req (i.e., the generic
>> + * hold-off mechanism provided by the ring macros). Backends must set
>> + * xendispl_req appropriately (e.g., using RING_FINAL_CHECK_FOR_REQUESTS()).
>> + *
>> + * Back->front notifications: when enqueuing a new response, sending a
>> + * notification can be made conditional on xendispl_resp (i.e., the generic
>> + * hold-off mechanism provided by the ring macros). Frontends must set
>> + * xendispl_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
>> + *
>> + * The two halves of a para-virtual display driver utilize nodes within
>> + * XenStore to communicate capabilities and to negotiate operating parameters.
>> + * This section enumerates these nodes which reside in the respective front and
>> + * backend portions of XenStore, following the XenBus convention.
>> + *
>> + * All data in XenStore is stored as strings. Nodes specifying numeric
>> + * values are encoded in decimal. Integer value ranges listed below are
>> + * expressed as fixed sized integer types capable of storing the conversion
>> + * of a properly formated node string, without loss of information.
>> + *
>> + ******************************************************************************
>> + *                        Example configuration
>> + ******************************************************************************
>> + *
>> + * Note: depending on the use-case backend can expose more display connectors
>> + * than the underlying HW physically has by employing SW graphics compositors
>> + *
>> + * This is an example of backend and frontend configuration:
>> + *
>> + *--------------------------------- Backend -----------------------------------
>> + *
>> + * /local/domain/0/backend/vdispl/1/0/frontend-id = "1"
>> + * /local/domain/0/backend/vdispl/1/0/frontend = "/local/domain/1/device/vdispl/0"
>> + * /local/domain/0/backend/vdispl/1/0/state = "4"
>> + * /local/domain/0/backend/vdispl/1/0/versions = "1,2"
>> + *
>> + *--------------------------------- Frontend ----------------------------------
>> + *
>> + * /local/domain/1/device/vdispl/0/backend-id = "0"
>> + * /local/domain/1/device/vdispl/0/backend = "/local/domain/0/backend/vdispl/1/0"
>> + * /local/domain/1/device/vdispl/0/state = "4"
>> + * /local/domain/1/device/vdispl/0/version = "1"
>> + * /local/domain/1/device/vdispl/0/be_alloc = "1"
>
> This could be changed to '-'. As in "be-alloc" instead of "be_alloc"
>> + *
>> + *-------------------------- Connector 0 configuration ------------------------
>> + *
>> + * /local/domain/1/device/vdispl/0/0/resolution = "1920x1080"
>> + * /local/domain/1/device/vdispl/0/0/req-ring-ref = "2832"
>> + * /local/domain/1/device/vdispl/0/0/req-event-channel = "15"
>> + * /local/domain/1/device/vdispl/0/0/evt-ring-ref = "387"
>> + * /local/domain/1/device/vdispl/0/0/evt-event-channel = "16"
>> + *
>> + *-------------------------- Connector 1 configuration ------------------------
>> + *
>> + * /local/domain/1/device/vdispl/0/1/resolution = "800x600"
>> + * /local/domain/1/device/vdispl/0/1/req-ring-ref = "2833"
>> + * /local/domain/1/device/vdispl/0/1/req-event-channel = "17"
>> + * /local/domain/1/device/vdispl/0/1/evt-ring-ref = "388"
>> + * /local/domain/1/device/vdispl/0/1/evt-event-channel = "18"
>> + *
>> + ******************************************************************************
>> + *                            Backend XenBus Nodes
>> + ******************************************************************************
>> + *
>> + *----------------------------- Protocol version ------------------------------
>> + *
>> + * versions
>> + *      Values:         <string>
>> + *
>> + *      List of XENDISPL_LIST_SEPARATOR separated protocol versions supported
>> + *      by the backend. For example "1,2,3".
>> + *
>> + ******************************************************************************
>> + *                            Frontend XenBus Nodes
>> + ******************************************************************************
>> + *
>> + *-------------------------------- Addressing ---------------------------------
>> + *
>> + * dom-id
>> + *      Values:         <uint16_t>
>> + *
>> + *      Domain identifier.
>> + *
>> + * dev-id
>> + *      Values:         <uint16_t>
>> + *
>> + *      Device identifier.
>> + *
>> + * conn-idx
>> + *      Values:         <uint8_t>
>> + *
>> + *      Zero based contigous index of the connector.
>> + *      /local/domain/<dom-id>/device/vdispl/<dev-id>/<conn-idx>/...
>> + *
>> + *----------------------------- Protocol version ------------------------------
>> + *
>> + * version
>> + *      Values:         <string>
>> + *
>> + *      Protocol version, chosen among the ones supported by the backend.
>> + *
>> + *------------------------- Backend buffer allocation -------------------------
>> + *
>> + * be_alloc
>> + *      Values:         "0", "1"
>> + *
>> + *      If value is set to "1", then backend can be a buffer provider/allocator
>> + *      for this domain during XENDISPL_OP_DBUF_CREATE operation (see below
>> + *      for negotiation).
>> + *      If value is not "1" or omitted frontend must allocate buffers itself.
>> + *
>> + *----------------------------- Connector settings ----------------------------
>> + *
>> + * resolution
>> + *      Values:         <width, uint32_t>x<height, uint32_t>
>> + *
>> + *      Width and height of the connector in pixels separated by
>> + *      XENDISPL_RESOLUTION_SEPARATOR. This defines visible area of the
>> + *      display.
>> + *
>> + *------------------ Connector Request Transport Parameters -------------------
>> + *
>> + * This communication path is used to deliver requests from frontend to backend
>> + * and get the corresponding responses from backend to frontend,
>> + * set up per connector.
>> + *
>> + * req-event-channel
>> + *      Values:         <uint32_t>
>> + *
>> + *      The identifier of the Xen connector's control event channel
>> + *      used to signal activity in the ring buffer.
>> + *
>> + * req-ring-ref
>> + *      Values:         <uint32_t>
>> + *
>> + *      The Xen grant reference granting permission for the backend to map
>> + *      a sole page in a single page sized connector's control ring buffer.
> Perhaps s/in a single page sized/of/ ?
>
>
>> + *
>> + *------------------- Connector Event Transport Parameters --------------------
>> + *
>> + * This communication path is used to deliver asynchronous events from backend
>> + * to frontend, set up per connector.
>> + *
>> + * evt-event-channel
>> + *      Values:         <uint32_t>
>> + *
>> + *      The identifier of the Xen connector's event channel
>> + *      used to signal activity in the ring buffer.
>> + *
>> + * evt-ring-ref
>> + *      Values:         <uint32_t>
>> + *
>> + *      The Xen grant reference granting permission for the backend to map
>> + *      a sole page in a single page sized connector's event ring buffer.
> The same here? s/in a single page sized/of/
>> + */
>> +
>> +/*
>> + ******************************************************************************
>> + *                               STATE DIAGRAMS
>> + ******************************************************************************
>> + *
>> + * Tool stack creates front and back state nodes with initial state
>> + * XenbusStateInitialising.
>> + * Tool stack creates and sets up frontend display configuration
>> + * nodes per domain.
>> + *
>> + *-------------------------------- Normal flow --------------------------------
>> + *
>> + * Front                                Back
>> + * =================================    =====================================
>> + * XenbusStateInitialising              XenbusStateInitialising
>> + *                                       o Query backend device identification
>> + *                                         data.
>> + *                                       o Open and validate backend device.
>> + *                                                |
>> + *                                                |
>> + *                                                V
>> + *                                      XenbusStateInitWait
>> + *
>> + * o Query frontend configuration
>> + * o Allocate and initialize
>> + *   event channels per configured
>> + *   connector.
>> + * o Publish transport parameters
>> + *   that will be in effect during
>> + *   this connection.
>> + *              |
>> + *              |
>> + *              V
>> + * XenbusStateInitialised
>> + *
>> + *                                       o Query frontend transport parameters.
>> + *                                       o Connect to the event channels.
>> + *                                                |
>> + *                                                |
>> + *                                                V
>> + *                                      XenbusStateConnected
>> + *
>> + *  o Create and initialize OS
>> + *    virtual display connectors
>> + *    as per configuration.
>> + *              |
>> + *              |
>> + *              V
>> + * XenbusStateConnected
>> + *
>> + *                                      XenbusStateUnknown
>> + *                                      XenbusStateClosed
>> + *                                      XenbusStateClosing
>> + * o Remove virtual display device
>> + * o Remove event channels
>> + *              |
>> + *              |
>> + *              V
>> + * XenbusStateClosed
>> + *
>> + *------------------------------- Recovery flow -------------------------------
>> + *
>> + * In case of frontend unrecoverable errors backend handles that as
>> + * if frontend goes into the XenbusStateClosed state.
>> + *
>> + * In case of backend unrecoverable errors frontend tries removing
>> + * the virtualized device. If this is possible at the moment of error,
>> + * then frontend goes into the XenbusStateInitialising state and is ready for
>> + * new connection with backend. If the virtualized device is still in use and
>> + * cannot be removed, then frontend goes into the XenbusStateReconfiguring state
>> + * until either the virtualized device removed or backend initiates a new
> s/removed/is removed/
>
>> + * connection. On the virtualized device removal frontend goes into the
>> + * XenbusStateInitialising state.
>> + *
>> + * Note on XenbusStateReconfiguring state of the frontend: if backend has
>> + * unrecoverable errors then frontend cannot send requests to the backend
>> + * and thus cannot provide functionality of the virtualized device anymore.
>> + * After backend is back to normal the virtualized device may still hold some
>> + * state: configuration in use, allocated buffers, client application state etc.
>> + * So, in most cases, this will require frontend to implement complex recovery
> s/So, in/In/
>> + * reconnect logic. Instead, by going into XenbusStateReconfiguring state,
>> + * frontend will make sure no new clients of the virtualized device are
>> + * accepted, allow existing client(s) to exit gracefully by signaling error
>> + * state etc.
>> + * Once all the clients are gone frontend can reinitialize the virtualized
>> + * device and get into XenbusStateInitialising state again signaling the
>> + * backend that a new connection can be made.
>> + *
>> + * There are multiple conditions possible under which frontend will go from
>> + * XenbusStateReconfiguring into XenbusStateInitialising, some of them are OS
>> + * specific. For example:
>> + * 1. The underlying OS framework may provide callbacks to signal that the last
>> + *    client of the virtualized device has gone and the device can be removed
>> + * 2. Frontend can schedule a deferred work (timer/tasklet/workqueue)
>> + *    to periodically check if this is the right time to re-try removal of
>> + *    the virtualized device.
>> + * 3. By any other means.
>> + *
>> + ******************************************************************************
>> + *                             REQUEST CODES
>> + ******************************************************************************
>> + * Request codes [0; 15] are reserved and must not be used
>> + */
>> +
>> +#define XENDISPL_OP_DBUF_CREATE       0x10
>> +#define XENDISPL_OP_DBUF_DESTROY      0x11
>> +#define XENDISPL_OP_FB_ATTACH         0x12
>> +#define XENDISPL_OP_FB_DETACH         0x13
>> +#define XENDISPL_OP_SET_CONFIG        0x14
>> +#define XENDISPL_OP_PG_FLIP           0x15
>> +
>> +/*
>> + ******************************************************************************
>> + *                                 EVENT CODES
>> + ******************************************************************************
>> + */
>> +#define XENDISPL_EVT_PG_FLIP          0x00
>> +
>> +/*
>> + ******************************************************************************
>> + *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
>> + ******************************************************************************
>> + */
>> +#define XENDISPL_DRIVER_NAME          "vdispl"
>> +
>> +#define XENDISPL_LIST_SEPARATOR       ","
>> +#define XENDISPL_RESOLUTION_SEPARATOR "x"
>> +
>> +#define XENDISPL_FIELD_BE_VERSIONS    "versions"
>> +#define XENDISPL_FIELD_FE_VERSION     "version"
>> +#define XENDISPL_FIELD_REQ_RING_REF   "req-ring-ref"
>> +#define XENDISPL_FIELD_REQ_CHANNEL    "req-event-channel"
>> +#define XENDISPL_FIELD_EVT_RING_REF   "evt-ring-ref"
>> +#define XENDISPL_FIELD_EVT_CHANNEL    "evt-event-channel"
>> +#define XENDISPL_FIELD_RESOLUTION     "resolution"
>> +#define XENDISPL_FIELD_BE_ALLOC       "be_alloc"
> s/be_alloc/be-alloc/ ?
>
>
>> +
>> +/*
>> + ******************************************************************************
>> + *                          STATUS RETURN CODES
>> + ******************************************************************************
>> + *
>> + * Status return code is zero on success and -XEN_EXX on failure.
>> + *
>> + ******************************************************************************
>> + *                              Assumptions
>> + ******************************************************************************
>> + * o usage of grant reference 0 as invalid grant reference:
>> + *   grant reference 0 is valid, but never exposed to a PV driver,
>> + *   because of the fact it is already in use/reserved by the PV console.
>> + * o all references in this document to page sizes must be treated
>> + *   as pages of size XEN_PAGE_SIZE unless otherwise noted.
>> + *
>> + ******************************************************************************
>> + *       Description of the protocol between frontend and backend driver
>> + ******************************************************************************
>> + *
>> + * The two halves of a Para-virtual display driver communicate with
>> + * each other using shared pages and event channels.
>> + * Shared page contains a ring with request/response packets.
>> + *
>> + * All reserved fields in the structures below must be 0.
>> + * Display buffers's cookie of value 0 treated as invalid.
> s/treated/is treated/
>> + * Framebuffer's cookie of value 0 treated as invalid.
> s/treated/is treated/
>> + *
>> + * For all request/response/event packets that use cookies:
>> + *   dbuf_cookie - uint64_t, unique to guest domain value used by the backend
>> + *     to map remote display buffer to its local one
>> + *   fb_cookie - uint64_t, unique to guest domain value used by the backend
>> + *     to map remote framebuffer to its local one
>> + *
>> + *---------------------------------- Requests ---------------------------------
>> + *
>> + * All requests/responses, which are not connector specific, must be sent over
>> + * control ring of the connector with index 0.
> s/with index 0/which has the index value of 0/ ?
>
> [and for the four other places]. The 'with index 0' got me thinking that the
> structure has to have some index 0. But you mean that it should go over:
>
> /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
>
> Perhaps include that? Like:
>
> "
> control ring of the connector which has the index value of 0:
> /local/domain/<dom-id>/device/vdispl/<dev-id>/0/req-ring-ref
>
> "?
>
>> + *
>> + * All request packets have the same length (64 octets)
>> + * All request packets have common header:
>> + *         0                1                 2               3        octet
>> + * +----------------+----------------+----------------+----------------+
>> + * |               id                |    operation   |   reserved     | 4
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 8
>> + * +----------------+----------------+----------------+----------------+
>> + *   id - uint16_t, private guest value, echoed in response
>> + *   operation - uint8_t, operation code, XENDISPL_OP_???
>> + *
>> + * Request dbuf creation - request creation of a display buffer.
>> + *         0                1                 2               3        octet
>> + * +----------------+----------------+----------------+----------------+
>> + * |               id                |_OP_DBUF_CREATE |   reserved     | 4
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 8
>> + * +----------------+----------------+----------------+----------------+
>> + * |                       dbuf_cookie low 32-bit                      | 12
>> + * +----------------+----------------+----------------+----------------+
>> + * |                       dbuf_cookie high 32-bit                     | 16
>> + * +----------------+----------------+----------------+----------------+
>> + * |                               width                               | 20
>> + * +----------------+----------------+----------------+----------------+
>> + * |                               height                              | 24
>> + * +----------------+----------------+----------------+----------------+
>> + * |                                bpp                                | 28
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             buffer_sz                             | 32
>> + * +----------------+----------------+----------------+----------------+
>> + * |                               flags                               | 36
>> + * +----------------+----------------+----------------+----------------+
>> + * |                           gref_directory                          | 40
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 44
>> + * +----------------+----------------+----------------+----------------+
>> + * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
>> + * +----------------+----------------+----------------+----------------+
>> + * |                             reserved                              | 64
>> + * +----------------+----------------+----------------+----------------+
>> + *
>> + * Must be sent over control ring of the connector with index 0.
>> + * All unused bits in flags field must be set to 0.
>> + *
>> + * An attempt to create multiple display buffers with the same dbuf_cookie is
>> + * an error. dbuf_cookie can be re-used after destroying the corresponding
>> + * display buffer.
>> + *
>> + * Width and height of the display buffers can be smaller, equal or bigger
>> + * than the connector's resolution. Depth/pixel format of the individual
>> + * buffers can differ as well.
>> + *
>> + * width - uint32_t, width in pixels
>> + * height - uint32_t, height in pixels
>> + * bpp - uint32_t, bits per pixel
>> + * buffer_sz - uint32_t, buffer size to be allocated, octets
>> + * flags - uint32_t, flags of the operation
>> + *   o XENDISPL_DBUF_FLG_REQ_ALLOC - if set, then backend is requested
>> + *     to allocate the buffer with the parameters provided in this request.
>> + *     Page directory is handled as follows:
>> + *       Frontend on request:
>> + *         o allocates pages for the directory (gref_directory,
>> + *           gref_dir_next_page(s)
>> + *         o grants permissions for the pages of the directory
> .. to the backend.
>> + *         o sets gref_dir_next_page fields
>> + *       Backend on response:
>> + *         o grants permissions for the pages of the buffer allocated
> .. to the frontend
>> + *         o fills in page directory with grant references
>> + *           (gref[] in struct xendispl_page_directorygref)
> s/directorygref/xendispl_page_directory
>
>> + * gref_directory - grant_ref_t, a reference to the first shared page
>> + *   describing shared buffer references. At least one page exists. If shared
>> + *   buffer size (buffer_sz) exceeds what can be addressed by this single page,
>> + *   then reference to the next page must be supplied (see gref_dir_next_page
>> + *   below)
>> + */
>> +
> .. snip..
>> + ******************************************************************************
>> + *                        Back to front events delivery
>> + ******************************************************************************
>> + * In order to deliver asynchronous events from back to front a shared page is
>> + * allocated by front and its granted reference propagated to back via
>> + * XenStore entries (event-XXX).
>
> s/event-XXXX/.. the right name?/
>
>> + * This page has a common header used by both front and back to synchronize
>> + * access and control event's ring buffer, while back being a producer of the
>> + * events and front being a consumer. The rest of the page after the header
>> + * is used for event packets.
>> + *
>> + * Upon reception of an event(s) front may confirm its reception
>> + * for either each event, group of events or none.
>> + */
>> +
>> +struct xendispl_event_page {
>> +    uint32_t in_cons;
>> +    uint32_t in_prod;
>> +    uint8_t reserved[56];
>> +};
>> +
>> +#define XENDISPL_EVENT_PAGE_SIZE 4096
>> +#define XENDISPL_IN_RING_OFFS (sizeof(struct xendispl_event_page))
>> +#define XENDISPL_IN_RING_SIZE (XENDISPL_EVENT_PAGE_SIZE - XENDISPL_IN_RING_OFFS)
>> +#define XENDISPL_IN_RING_LEN (XENDISPL_IN_RING_SIZE / sizeof(struct xendispl_evt))
>> +#define XENDISPL_IN_RING(page) \
>> +	((struct xendispl_evt *)((char *)(page) + XENDISPL_IN_RING_OFFS))
>> +#define XENDISPL_IN_RING_REF(page, idx) \
>> +	(XENDISPL_IN_RING((page))[(idx) % XENDISPL_IN_RING_LEN])
>> +
>> +#endif /* __XEN_PUBLIC_IO_DISPLIF_H__ */
>> +
>> +/*
>> + * Local variables:
>> + * mode: C
>> + * c-file-style: "BSD"
>> + * c-basic-offset: 4
>> + * tab-width: 4
>> + * indent-tabs-mode: nil
>> + * End:
>> + */
>> -- 
>> 2.7.4
>>
Thank you,
Oleksandr

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Re: [PATCH v4] displif: add ABI for para-virtual display

[Konrad Rzeszutek Wilk]

.snip..
> > + *----------------------------- Protocol version ------------------------------
> > + *
> > + * version
> > + *      Values:         <string>
> > + *
> > + *      Protocol version, chosen among the ones supported by the backend.
> > + *
..snip..
> > +#define XENDISPL_FIELD_BE_VERSIONS    "versions"
> > +#define XENDISPL_FIELD_FE_VERSION     "version"

I couldn't find in spec what version this actually is. As in I would
assume it is version 1, but that is not enumerated.

Perhaps it may be good to include in the Backend section that the
'versions' will contain the value 1. And that future changes would
update it?



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Re: [PATCH v4] displif: add ABI for para-virtual display

[Oleksandr Andrushchenko]

On 04/04/2017 11:07 PM, Konrad Rzeszutek Wilk wrote:
> .snip..
>>> + *----------------------------- Protocol version ------------------------------
>>> + *
>>> + * version
>>> + *      Values:         <string>
>>> + *
>>> + *      Protocol version, chosen among the ones supported by the backend.
>>> + *
> ..snip..
>>> +#define XENDISPL_FIELD_BE_VERSIONS    "versions"
>>> +#define XENDISPL_FIELD_FE_VERSION     "version"
> I couldn't find in spec what version this actually is. As in I would
> assume it is version 1, but that is not enumerated.
We have:
+ * versions
+ *      Values:         <string>
+ *
+ *      List of XENDISPL_LIST_SEPARATOR separated protocol versions 
supported
+ *      by the backend. For example "1,2,3".
which defines the format of the versions enumeration.
> Perhaps it may be good to include in the Backend section that the
> 'versions' will contain the value 1.
I will probably put something like
#define XENDISPL_PROTOCOL_VERSION "1"
on top, which will particularly used by the backend too:
on top, because this value is not only for backend, but
overall protocol identificator
>   And that future changes would
> update it?
Thus, once we need to change it we are all set
>
I will release v5 today with the change above and your comments fixed

Thank you,
Oleksandr

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