[PATCH v2 1/1] cameraif: add ABI for para-virtual camera

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

This is the ABI for the two halves of a para-virtualized
camera driver which extends Xen's reach multimedia capabilities even
farther enabling it for video conferencing, In-Vehicle Infotainment,
high definition maps etc.

The initial goal is to support most needed functionality with the
final idea to make it possible to extend the protocol if need be:

1. Provide means for base virtual device configuration:
 - pixel formats
 - resolutions
 - frame rates
2. Support basic camera controls:
 - contrast
 - brightness
 - hue
 - saturation
3. Support streaming control
4. Support zero-copying use-cases

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 xen/include/public/io/cameraif.h | 1263 ++++++++++++++++++++++++++++++
 1 file changed, 1263 insertions(+)
 create mode 100644 xen/include/public/io/cameraif.h

diff --git a/xen/include/public/io/cameraif.h b/xen/include/public/io/cameraif.h
new file mode 100644
index 000000000000..38b9b3741e75
--- /dev/null
+++ b/xen/include/public/io/cameraif.h
@@ -0,0 +1,1263 @@
+/******************************************************************************
+ * cameraif.h
+ *
+ * Unified camera 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) 2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_PUBLIC_IO_CAMERAIF_H__
+#define __XEN_PUBLIC_IO_CAMERAIF_H__
+
+#include "ring.h"
+#include "../grant_table.h"
+
+/*
+ ******************************************************************************
+ *                           Protocol version
+ ******************************************************************************
+ */
+#define XENCAMERA_PROTOCOL_VERSION     "1"
+
+/*
+ ******************************************************************************
+ *                  Feature and Parameter Negotiation
+ ******************************************************************************
+ *
+ * Front->back notifications: when enqueuing a new request, sending a
+ * notification can be made conditional on xencamera_req (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Backends must set
+ * xencamera_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 xencamera_resp (i.e., the generic
+ * hold-off mechanism provided by the ring macros). Frontends must set
+ * xencamera_resp appropriately (e.g., using RING_FINAL_CHECK_FOR_RESPONSES()).
+ *
+ * The two halves of a para-virtual camera 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 formatted node string, without loss of information.
+ *
+ ******************************************************************************
+ *                        Example configuration
+ ******************************************************************************
+ *
+ * This is an example of backend and frontend configuration:
+ *
+ *--------------------------------- Backend -----------------------------------
+ *
+ * /local/domain/0/backend/vcamera/1/0/frontend-id = "1"
+ * /local/domain/0/backend/vcamera/1/0/frontend = "/local/domain/1/device/vcamera/0"
+ * /local/domain/0/backend/vcamera/1/0/state = "4"
+ * /local/domain/0/backend/vcamera/1/0/versions = "1,2"
+ *
+ *--------------------------------- Frontend ----------------------------------
+ *
+ * /local/domain/1/device/vcamera/0/backend-id = "0"
+ * /local/domain/1/device/vcamera/0/backend = "/local/domain/0/backend/vcamera/1"
+ * /local/domain/1/device/vcamera/0/state = "4"
+ * /local/domain/1/device/vcamera/0/version = "1"
+ * /local/domain/1/device/vcamera/0/be-alloc = "1"
+ *
+ *---------------------------- Device 0 configuration -------------------------
+ *
+ * /local/domain/1/device/vcamera/0/controls = "contrast,hue"
+ * /local/domain/1/device/vcamera/0/formats/YUYV/640x480/frame-rates = "30/1,15/1"
+ * /local/domain/1/device/vcamera/0/formats/YUYV/1920x1080/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/0/formats/BGRA/640x480/frame-rates = "15/1,15/2"
+ * /local/domain/1/device/vcamera/0/formats/BGRA/1200x720/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/0/unique-id = "0"
+ * /local/domain/1/device/vcamera/0/req-ring-ref = "2832"
+ * /local/domain/1/device/vcamera/0/req-event-channel = "15"
+ * /local/domain/1/device/vcamera/0/evt-ring-ref = "387"
+ * /local/domain/1/device/vcamera/0/evt-event-channel = "16"
+ *
+ *---------------------------- Device 1 configuration -------------------------
+ *
+ * /local/domain/1/device/vcamera/1/controls = "brightness,saturation,hue"
+ * /local/domain/1/device/vcamera/1/formats/YUYV/640x480/frame-rates = "30/1,15/2"
+ * /local/domain/1/device/vcamera/1/formats/YUYV/1920x1080/frame-rates = "15/2"
+ * /local/domain/1/device/vcamera/1/unique-id = "1"
+ * /local/domain/1/device/vcamera/1/req-ring-ref = "2833"
+ * /local/domain/1/device/vcamera/1/req-event-channel = "17"
+ * /local/domain/1/device/vcamera/1/evt-ring-ref = "388"
+ * /local/domain/1/device/vcamera/1/evt-event-channel = "18"
+ *
+ ******************************************************************************
+ *                            Backend XenBus Nodes
+ ******************************************************************************
+ *
+ *----------------------------- Protocol version ------------------------------
+ *
+ * versions
+ *      Values:         <string>
+ *
+ *      List of XENCAMERA_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.
+ *
+ *      /local/domain/<dom-id>/device/vcamera/<dev-id>/...
+ *
+ *----------------------------- 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 will be the buffer
+ *      provider/allocator for this domain during XENCAMERA_OP_BUF_CREATE
+ *      operation.
+ *      If value is not "1" or omitted frontend must allocate buffers itself.
+ *
+ *------------------------------- Camera settings -----------------------------
+ *
+ * unique-id
+ *      Values:         <string>
+ *
+ *      After device instance initialization each camera is assigned a
+ *      unique ID, so it can be identified by the backend by this ID.
+ *      This can be UUID or such.
+ *
+ * controls
+ *      Values:         <list of string>
+ *
+ *      List of supported camera controls separated by XENCAMERA_LIST_SEPARATOR.
+ *      Camera controls are expressed as a list of string values w/o any
+ *      ordering requirement.
+ *
+ * formats
+ *      Values:         <format, char[4]>
+ *
+ *      Formats are organized as a set of directories one per each
+ *      supported pixel format. The name of the directory is the
+ *      corresponding FOURCC string label. The next level of
+ *      the directory under <formats> represents supported resolutions.
+ *
+ * resolution
+ *      Values:         <width, uint32_t>x<height, uint32_t>
+ *
+ *      Resolutions are organized as a set of directories one per each
+ *      supported resolution under corresponding <formats> directory.
+ *      The name of the directory is the supported width and height
+ *      of the camera resolution in pixels.
+ *
+ * frame-rates
+ *      Values:         <numerator, uint32_t>/<denominator, uint32_t>
+ *
+ *      List of XENCAMERA_FRAME_RATE_SEPARATOR separated supported frame rates
+ *      of the camera expressed as numerator and denominator of the
+ *      corresponding frame rate.
+ *
+ *------------------- Camera 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 virtual camera device.
+ *
+ * req-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen camera'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 of camera's control ring buffer.
+ *
+ *-------------------- Camera Event Transport Parameters ----------------------
+ *
+ * This communication path is used to deliver asynchronous events from backend
+ * to frontend, set up per virtual camera device.
+ *
+ * evt-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen camera'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 of camera'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 camera 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
+ *   camera.
+ * 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 camera as per
+ *    configuration.
+ *              |
+ *              |
+ *              V
+ * XenbusStateConnected
+ *
+ *                                      XenbusStateUnknown
+ *                                      XenbusStateClosed
+ *                                      XenbusStateClosing
+ * o Remove virtual camera 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 is 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.
+ * 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
+ ******************************************************************************
+ */
+#define XENCAMERA_OP_CONFIG_SET        0x00
+#define XENCAMERA_OP_CONFIG_GET        0x01
+#define XENCAMERA_OP_BUF_REQUEST       0x02
+#define XENCAMERA_OP_BUF_CREATE        0x03
+#define XENCAMERA_OP_BUF_DESTROY       0x04
+#define XENCAMERA_OP_BUF_QUEUE         0x05
+#define XENCAMERA_OP_BUF_DEQUEUE       0x06
+#define XENCAMERA_OP_CTRL_ENUM         0x07
+#define XENCAMERA_OP_CTRL_SET          0x08
+#define XENCAMERA_OP_CTRL_GET          0x09
+#define XENCAMERA_OP_STREAM_START      0x0a
+#define XENCAMERA_OP_STREAM_STOP       0x0b
+
+#define XENCAMERA_CTRL_BRIGHTNESS      0
+#define XENCAMERA_CTRL_CONTRAST        1
+#define XENCAMERA_CTRL_SATURATION      2
+#define XENCAMERA_CTRL_HUE             3
+
+/* Number of supported controls. */
+#define XENCAMERA_MAX_CTRL             4
+
+/* Control is read-only. */
+#define XENCAMERA_CTRL_FLG_RO          (1 << 0)
+/* Control is write-only. */
+#define XENCAMERA_CTRL_FLG_WO          (1 << 1)
+/* Control's value is volatile. */
+#define XENCAMERA_CTRL_FLG_VOLATILE    (1 << 2)
+
+/* Supported color spaces. */
+#define XENCAMERA_COLORSPACE_SMPTE170M 0
+#define XENCAMERA_COLORSPACE_REC709    1
+#define XENCAMERA_COLORSPACE_SRGB      2
+#define XENCAMERA_COLORSPACE_ADOBERGB  3
+#define XENCAMERA_COLORSPACE_BT2020    4
+#define XENCAMERA_COLORSPACE_DCI_P3    5
+#define XENCAMERA_COLORSPACE_RAW       6
+
+/* Color space transfer function. */
+#define XENCAMERA_XFER_FUNC_709        0
+#define XENCAMERA_XFER_FUNC_SRGB       1
+#define XENCAMERA_XFER_FUNC_ADOBERGB   2
+#define XENCAMERA_XFER_FUNC_NONE       3
+#define XENCAMERA_XFER_FUNC_DCI_P3     4
+#define XENCAMERA_XFER_FUNC_SMPTE2084  5
+
+/* Color space Y’CbCr encoding. */
+#define XENCAMERA_YCBCR_ENC_601              0
+#define XENCAMERA_YCBCR_ENC_709              1
+#define XENCAMERA_YCBCR_ENC_XV601            2
+#define XENCAMERA_YCBCR_ENC_XV709            3
+#define XENCAMERA_YCBCR_ENC_BT2020           4
+#define XENCAMERA_YCBCR_ENC_BT2020_CONST_LUM 5
+
+/* Quantization range. */
+#define XENCAMERA_QUANTIZATION_FULL_RANGE    0
+#define XENCAMERA_QUANTIZATION_LIM_RANGE     1
+
+/*
+ ******************************************************************************
+ *                                 EVENT CODES
+ ******************************************************************************
+ */
+#define XENCAMERA_EVT_FRAME_AVAIL      0x00
+#define XENCAMERA_EVT_CONFIG_CHANGE    0x01
+#define XENCAMERA_EVT_CTRL_CHANGE      0x02
+
+/* Resolution has changed. */
+#define XENCAMERA_EVT_CFG_FLG_RESOL    (1 << 0)
+
+/*
+ ******************************************************************************
+ *               XENSTORE FIELD AND PATH NAME STRINGS, HELPERS
+ ******************************************************************************
+ */
+#define XENCAMERA_DRIVER_NAME          "vcamera"
+
+#define XENCAMERA_LIST_SEPARATOR       ","
+#define XENCAMERA_RESOLUTION_SEPARATOR "x"
+#define XENCAMERA_FRACTION_SEPARATOR   "/"
+
+#define XENCAMERA_FIELD_BE_VERSIONS    "versions"
+#define XENCAMERA_FIELD_FE_VERSION     "version"
+#define XENCAMERA_FIELD_REQ_RING_REF   "req-ring-ref"
+#define XENCAMERA_FIELD_REQ_CHANNEL    "req-event-channel"
+#define XENCAMERA_FIELD_EVT_RING_REF   "evt-ring-ref"
+#define XENCAMERA_FIELD_EVT_CHANNEL    "evt-event-channel"
+#define XENCAMERA_FIELD_CONTROLS       "controls"
+#define XENCAMERA_FIELD_FORMATS        "formats"
+#define XENCAMERA_FIELD_FRAME_RATES    "frame-rates"
+#define XENCAMERA_FIELD_BE_ALLOC       "be-alloc"
+#define XENCAMERA_FIELD_UNIQUE_ID      "unique-id"
+
+#define XENCAMERA_CTRL_BRIGHTNESS_STR  "brightness"
+#define XENCAMERA_CTRL_CONTRAST_STR    "contrast"
+#define XENCAMERA_CTRL_SATURATION_STR  "saturation"
+#define XENCAMERA_CTRL_HUE_STR         "hue"
+
+/* Maximum number of buffer planes supported. */
+#define XENCAMERA_MAX_PLANE            4
+
+/*
+ ******************************************************************************
+ *                          STATUS RETURN CODES
+ ******************************************************************************
+ *
+ * Status return code is zero on success and -XEN_EXX on failure.
+ *
+ ******************************************************************************
+ *                              Assumptions
+ ******************************************************************************
+ *
+ * - 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.
+ * - 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 camera 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.
+ *
+ * For all request/response/event packets:
+ *   - frame rate parameter is represented as a pair of 4 octet long
+ *     numerator and denominator:
+ *       - frame_rate_numer - uint32_t, numerator of the frame rate
+ *       - frame_rate_denom - uint32_t, denominator of the frame rate
+ *     The corresponding frame rate (Hz) is calculated as:
+ *       frame_rate = frame_rate_numer / frame_rate_denom
+ *   - buffer index is a zero based index of the buffer. Must be less than
+ *     the value of XENCAMERA_OP_CONFIG_SET.num_bufs response:
+ *       - index - uint8_t, index of the buffer.
+ *
+ *
+ *---------------------------------- Requests ---------------------------------
+ *
+ * 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, XENCAMERA_OP_XXX.
+ *
+ *
+ * Request to set configuration - request to set the configuration/mode
+ * of the camera:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_SET |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                            pixel format                           | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                             colorspace                            | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             xfer_func                             | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             ycbcr_enc                             | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                            quantization                           | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_numer                       | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_denom                       | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_numer                         | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_denom                         | 52
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 56
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * pixel_format - uint32_t, pixel format to be used, FOURCC code.
+ * width - uint32_t, width in pixels.
+ * height - uint32_t, height in pixels.
+ * colorspace - uint32_t, this supplements pixel_format parameter,
+ *   one of the XENCAMERA_COLORSPACE_XXX.
+ * xfer_func - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_XFER_FUNC_XXX.
+ * ycbcr_enc - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_YCBCR_ENC_XXX.
+ * quantization - uint32_t, this supplements colorspace parameter,
+ *   one of the XENCAMERA_QUANTIZATION_XXX.
+ * displ_asp_ratio_numer - uint32_t, numerator of the display aspect ratio.
+ * displ_asp_ratio_denom - uint32_t, denominator of the display aspect ratio.
+ * frame_rate_numer - uint32_t, numerator of the frame rate.
+ * frame_rate_denom - uint32_t, denominator of the frame rate.
+ *
+ * See response format for this request.
+ *
+ * Notes:
+ *  - frontend must check the corresponding response in order to see
+ *    if the values reported back by the backend do match the desired ones
+ *    and can be accepted.
+ *  - frontend may send multiple XENCAMERA_OP_CONFIG_SET requests before
+ *    sending XENCAMERA_OP_STREAM_START request to update or tune the
+ *    configuration.
+ */
+struct xencamera_config {
+    uint32_t pixel_format;
+    uint32_t width;
+    uint32_t height;
+    uint32_t colorspace;
+    uint32_t xfer_func;
+    uint32_t ycbcr_enc;
+    uint32_t quantization;
+    uint32_t displ_asp_ratio_numer;
+    uint32_t displ_asp_ratio_denom;
+    uint32_t frame_rate_numer;
+    uint32_t frame_rate_denom;
+};
+
+/*
+ * Request current configuration of the camera:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_GET |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ *
+ * Request number of buffers to be used:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_REQUEST|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |    num_bufs    |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * num_bufs - uint8_t, desired number of buffers to be used.
+ *
+ * See response format for this request.
+ *
+ * Notes:
+ *  - frontend must check the corresponding response in order to see
+ *    if the values reported back by the backend do match the desired ones
+ *    and can be accepted.
+ *  - frontend may send multiple XENCAMERA_OP_BUF_REQUEST requests before
+ *    sending XENCAMERA_OP_STREAM_START request to update or tune the
+ *    configuration.
+ */
+struct xencamera_buf_request {
+    uint8_t num_bufs;
+};
+
+/*
+ * Request camera buffer creation:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_CREATE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                           gref_directory                          | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * An attempt to create multiple buffers with the same index is an error.
+ * index can be re-used after destroying the corresponding camera buffer.
+ *
+ * index - uint8_t, index of the buffer to be created.
+ * gref_directory - grant_ref_t, a reference to the first shared page
+ *   describing shared buffer references. The size of the buffer is equal to
+ *   XENCAMERA_OP_GET_BUF_DETAILS.size response. At least one page exists. If
+ *   shared buffer size exceeds what can be addressed by this single page,
+ *   then reference to the next shared page must be supplied (see
+ *   gref_dir_next_page below).
+ *
+ * If XENCAMERA_FIELD_BE_ALLOC configuration entry is set, then backend will
+ * allocate the buffer with the parameters provided in this request and page
+ * directory is handled as follows:
+ *   Frontend on request:
+ *     - allocates pages for the directory (gref_directory,
+ *       gref_dir_next_page(s)
+ *     - grants permissions for the pages of the directory to the backend
+ *     - sets gref_dir_next_page fields
+ *   Backend on response:
+ *     - grants permissions for the pages of the buffer allocated to
+ *       the frontend
+ *     - fills in page directory with grant references
+ *       (gref[] in struct xencamera_page_directory)
+ */
+struct xencamera_buf_create_req {
+    uint8_t index;
+    uint8_t reserved[3];
+    grant_ref_t gref_directory;
+};
+
+/*
+ * Shared page for XENCAMERA_OP_BUF_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 XENCAMERA_OP_BUF_CREATE.
+ *
+ * Number of grant_ref_t entries in the whole page directory is not
+ * passed, but instead can be calculated as:
+ *   num_grefs_total = (XENCAMERA_OP_BUF_REQUEST.size + XEN_PAGE_SIZE - 1) /
+ *       XEN_PAGE_SIZE
+ */
+struct xencamera_page_directory {
+    grant_ref_t gref_dir_next_page;
+    grant_ref_t gref[1]; /* Variable length */
+};
+
+/*
+ * Request buffer destruction - destroy a previously allocated camera buffer:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_DESTROY|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the buffer to be destroyed.
+ *
+ *
+ * Request queueing of the buffer for backend use:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_BUF_QUEUE  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Notes:
+ *  - frontends must not access the buffer content after this request until
+ *    response to XENCAMERA_OP_BUF_DEQUEUE has been received.
+ *  - buffers must be queued to the backend before destroying them with
+ *    XENCAMERA_OP_BUF_DESTROY.
+ *
+ * index - uint8_t, index of the buffer to be queued.
+ *
+ *
+ * Request dequeueing of the buffer for frontend use:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_BUF_DEQUEUE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Notes:
+ *  - frontend is allowed to access the buffer content after the corresponding
+ *    response to this request.
+ *
+ * index - uint8_t, index of the buffer to be queued.
+ *
+ *
+ * Request camera control details:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_ENUM  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ * index - uint8_t, index of the control to be queried.
+ */
+struct xencamera_index {
+    uint8_t index;
+};
+
+/*
+ * Request camera control change:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |  _OP_SET_CTRL  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ */
+struct xencamera_ctrl_value {
+    uint8_t type;
+    uint8_t reserved[7];
+    int64_t value;
+};
+
+/*
+ * Request camera control state:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |  _OP_GET_CTRL  |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * See response format for this request.
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ */
+struct xencamera_get_ctrl_req {
+    uint8_t type;
+};
+
+/*
+ * Request camera capture stream start:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_STREAM_START|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ *
+ * Request camera capture stream stop:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_STREAM_STOP |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ *
+ *---------------------------------- Responses --------------------------------
+ *
+ * All response packets have the same length (64 octets).
+ *
+ * All response packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, copied from the request.
+ * operation - uint8_t, XENCAMERA_OP_* - copied from request.
+ * status - int32_t, response status, zero on success and -XEN_EXX on failure.
+ *
+ *
+ * Set/get configuration response - response for XENCAMERA_OP_CONFIG_SET
+ * and XENCAMERA_OP_CONFIG_GET
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CONFIG_?ET |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                            pixel format                           | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                               width                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                               height                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                             colorspace                            | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             xfer_func                             | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             ycbcr_enc                             | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                            quantization                           | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_numer                       | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                       displ_asp_ratio_denom                       | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_numer                         | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                          frame_rate_denom                         | 52
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 56
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Meaning of the corresponding values in this response is the same as for
+ * XENCAMERA_OP_CONFIG_SET request.
+ *
+ *
+ * Request buffer response - response for XENCAMERA_OP_BUF_REQUEST
+ * request:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_OP_BUF_REQUEST |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |   num_buffers  |   num_planes   |            reserved             | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                                size                               | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_offset[0]                          | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_offset[1]                          | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_offset[2]                          | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                          plane_offset[3]                          | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[0]                           | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[1]                           | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[2]                           | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                           plane_size[3]                           | 48
+ * +----------------+----------------+----------------+----------------+
+ * |         plane_stride[0]         |         plane_stride[1]         | 52
+ * +----------------+----------------+----------------+----------------+
+ * |         plane_stride[2]         |         plane_stride[3]         | 56
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 60
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * num_buffers - uint8_t, number of buffers to be used.
+ * num_planes - uint8_t, number of planes of the buffer.
+ * size - uint32_t, overall size of the buffer including sizes of the
+ *   individual planes and padding if applicable.
+ * plane_offset - array of uint32_t, offset of the corresponding plane
+ *   in octets from the buffer start.
+ * plane_size - array of uint32_t, size in octets of the corresponding plane
+ *   including padding.
+ * plane_stride - array of uint32_t, size in octets occupied by the
+ *   corresponding single image line including padding if applicable.
+ */
+struct xencamera_buf_request_resp {
+    uint8_t num_buffers;
+    uint8_t num_planes;
+    uint8_t reserved[2];
+    uint32_t size;
+    uint32_t plane_offset[XENCAMERA_MAX_PLANE];
+    uint32_t plane_size[XENCAMERA_MAX_PLANE];
+    uint16_t plane_stride[XENCAMERA_MAX_PLANE];
+};
+
+/*
+ * Control enumerate response - response for XENCAMERA_OP_CTRL_ENUM:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_ENUM  |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |     index      |      type      |              flags              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          min low 32-bits                          | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          min high 32-bits                         | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                          max low 32-bits                          | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                          max high 32-bits                         | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                         step low 32-bits                          | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                         step high 32-bits                         | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                        def_val low 32-bits                        | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                        def_val high 32-bits                       | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 52
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the camera control in response.
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * flags - uint16_t, flags of the control, one of the XENCAMERA_CTRL_FLG_XXX.
+ * min - int64_t, minimum value of the control.
+ * max - int64_t, maximum value of the control.
+ * step - int64_t, minimum size in which control value can be changed.
+ * def_val - int64_t, default value of the control.
+ */
+struct xencamera_ctrl_enum_resp {
+    uint8_t index;
+    uint8_t type;
+    uint16_t flags;
+    uint8_t reserved[4];
+    int64_t min;
+    int64_t max;
+    int64_t step;
+    int64_t def_val;
+};
+
+/*
+ * Get control response - response for XENCAMERA_OP_CTRL_GET:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _OP_CTRL_GET   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                               status                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ */
+
+/*
+ *----------------------------------- 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.
+ *
+ *
+ * Frame captured event - event from back to front when a new captured
+ * frame is available:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_EVT_FRAME_AVAIL|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      index     |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                              used_sz                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                        seq_num low 32-bits                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                        seq_num high 32-bits                       | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * index - uint8_t, index of the buffer that contains new captured frame.
+ * used_sz - uint32_t, number of octets this frame has. This can be less
+ * than the XENCAMERA_OP_BUF_REQUEST.size (response) for compressed formats.
+ * seq_num - uint64_t, sequential number of the frame.
+ */
+struct xencamera_frame_avail_evt {
+    uint8_t index;
+    uint8_t reserved0[3];
+    uint32_t used_sz;
+    uint8_t reserved1[4];
+    uint64_t seq_num;
+};
+
+/*
+ * Configuration change - event from back to front when current
+ * configuration has changed:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                | _CONFIG_CHANGE |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                               flags                               | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * flags - uint32_t, set of the XENCAMERA_EVT_CFG_FLG_XXX flags.
+ */
+struct xencamera_cfg_change_evt {
+    uint32_t flags;
+};
+
+/*
+ * Control change event- event from back to front when camera control
+ * has changed:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |_EVT_CTRL_CHANGE|   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |       type     |                     reserved                     | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                          value low 32-bit                         | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                          value high 32-bit                        | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 28
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, type of the control, one of the XENCAMERA_CTRL_XXX.
+ * value - int64_t, new value of the control.
+ */
+
+
+struct xencamera_req {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved[5];
+    union {
+        struct xencamera_config config;
+        struct xencamera_buf_request buf_request;
+        struct xencamera_buf_create_req buf_create;
+        struct xencamera_index index;
+        struct xencamera_ctrl_value ctrl_value;
+        struct xencamera_get_ctrl_req get_ctrl;
+        uint8_t reserved[56];
+    } req;
+};
+
+struct xencamera_resp {
+    uint16_t id;
+    uint8_t operation;
+    uint8_t reserved;
+    int32_t status;
+    union {
+        struct xencamera_config config;
+        struct xencamera_buf_request_resp buf_request;
+        struct xencamera_ctrl_enum_resp ctrl_enum;
+        struct xencamera_ctrl_value ctrl_value;
+        uint8_t reserved1[56];
+    } resp;
+};
+
+struct xencamera_evt {
+    uint16_t id;
+    uint8_t type;
+    uint8_t reserved[5];
+    union {
+        struct xencamera_frame_avail_evt frame_avail;
+        struct xencamera_cfg_change_evt cfg_change;
+        struct xencamera_ctrl_value ctrl_value;
+        uint8_t reserved[56];
+    } evt;
+};
+
+DEFINE_RING_TYPES(xen_cameraif, struct xencamera_req, struct xencamera_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 (evt-ring-ref/evt-event-channel).
+ * 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 xencamera_event_page {
+    uint32_t in_cons;
+    uint32_t in_prod;
+    uint8_t reserved[56];
+};
+
+#define XENCAMERA_EVENT_PAGE_SIZE 4096
+#define XENCAMERA_IN_RING_OFFS (sizeof(struct xencamera_event_page))
+#define XENCAMERA_IN_RING_SIZE (XENCAMERA_EVENT_PAGE_SIZE - XENCAMERA_IN_RING_OFFS)
+#define XENCAMERA_IN_RING_LEN (XENCAMERA_IN_RING_SIZE / sizeof(struct xencamera_evt))
+#define XENCAMERA_IN_RING(page) \
+    ((struct xencamera_evt *)((char *)(page) + XENCAMERA_IN_RING_OFFS))
+#define XENCAMERA_IN_RING_REF(page, idx) \
+    (XENCAMERA_IN_RING((page))[(idx) % XENCAMERA_IN_RING_LEN])
+
+#endif /* __XEN_PUBLIC_IO_CAMERAIF_H__ */
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * tab-width: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
2.18.0


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