[PATCH v17 1/6] fpga: add bindings document for fpga region

Alan Tull
2016-02-25T23:28:09Z

New bindings document for FPGA Region to support programming
FPGA's under Device Tree control

Signed-off-by: Alan Tull <atull@opensource.altera.com>
Signed-off-by: Moritz Fischer <moritz.fischer@ettus.com>
---
v9: initial version added to this patchset
v10: s/fpga/FPGA/g
replace DT overlay example with slightly more complicated example
move to staging/simple-fpga-bus
v11: No change in this patch for v11 of the patch set
v12: Moved out of staging.
Changed to use FPGA bridges framework instead of resets
for bridges.
v13: bridge@0xff20000 -> bridge@ff200000, etc
Leave out directly talking about overlays
Remove regs and clocks directly under simple-fpga-bus in example
Use common "firmware-name" binding instead of "fpga-firmware"
v14: Use firmware-name in bindings description
Call it FPGA Area
Remove bindings that specify FPGA Manager and FPGA Bridges
v15: Cleanup as per Rob's comments
Combine usage doc with bindings document
Document as being Altera specific
Additions and changes to add FPGA Bus
v16: Reworked to document FPGA Regions
rename altera-fpga-bus-fpga-area.txt -> fpga-region.txt
Remove references that made it sound exclusive to Altera
Remove altr, prefix from fpga-bus and fpga-area compatible strings
Added Moritz' usage example with Xilinx
Cleaned up unit addresses
v17: Lots of rewrites to try to make things clearer
Clarify that overlay can be rejected if FPGA isn't programmed
Add external-fpga-config binding already used in u-boot
Change partial-reconfig binding to partial-fpga-config to align
with existing u-boot binding format *-fpga-config
Add a document from Xilinx' website
---
.../devicetree/bindings/fpga/fpga-region.txt | 491 ++++++++++++++++++++
1 file changed, 491 insertions(+)
create mode 100644 Documentation/devicetree/bindings/fpga/fpga-region.txt

diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt b/Documentation/devicetree/bindings/fpga/fpga-region.txt
new file mode 100644
index 0000000..141274f
--- /dev/null
+++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt
@@ -0,0 +1,491 @@
+FPGA Region Device Tree Binding
+
+Alan Tull 2016
+
+ CONTENTS
+ - Introduction
+ - Terminology
+ - Overview
+ - Constraints
+ - FPGA Region
+ - Supported Use Models
+ - Sequence
+ - Device Tree Examples
+
+
+Introduction
+============
+
+FPGA Regions are introduced as a way to solve the problem of how to program an
+FPGA under an operating system and have the new hardware show up in the device
+tree. By adding these bindings to the Device Tree, a system can have the
+information needed to program the FPGA and add the desired hardware, and also
+the information about the devices to be added to the Device Tree once the
+programming has succeeded.
+
+This device tree binding document hits some of the high points of FPGA usage and
+attempts to include terminology used by both major FPGA manufacturers. This
+document isn't a replacement for any manufacturers white papers and
+specifications for FPGA usage.
+
+
+Terminology
+===========
+
+Full Reconfiguration
+ * The entire FPGA is programmed.
+
+Partial Reconfiguration (PR)
+ * A section of the FPGA is reprogrammed while the rest of the FPGA is not
+ affected. Not all FPGA's support this.
+
+Partial Reconfiguration Region (PRR)
+ * Also called a "reconfigurable partition"
+ * A PRR is a specific section of a FPGA reserved for reconfiguration.
+ * A base (or static) FPGA image may create a set of PRR's that later may
+ be independently reprogrammed many times.
+ * The size and specific location of each PRR is fixed.
+ * The connections at the edge of each PRR are fixed. The image that is loaded
+ into a PRR must fit and must use a subset of the region's connections.
+ * The busses within the FPGA are split such that each region gets its own
+ branch that may be gated independently.
+
+Persona
+ * Also called a "partial bit stream"
+ * An FPGA image that is designed to be loaded into a PRR. There may be
+ any number of personas designed to fit into a PRR, but only one at at time
+ may be loaded.
+ * A persona may create more regions.
+
+FPGA Manager
+ * An FPGA Manager is a hardware block that programs an FPGA under the control
+ of a host processor.
+
+
+ ---------------- ------------------------------
+ | Host CPU | | FPGA |
+ | | | |
+ | ----| | ------- -------- |
+ | | H | | |==>| FB0 |<==>| PRR0 | |
+ | | W | | | ------- -------- |
+ | | | | | |
+ | | B |<=====>|<==| ------- -------- |
+ | | R | | |==>| FB1 |<==>| PRR1 | |
+ | | I | | | ------- -------- |
+ | | D | | | |
+ | | G | | | ------- -------- |
+ | | E | | |==>| FB1 |<==>| PRR1 | |
+ | ----| | ------- -------- |
+ | | | |
+ ---------------- ------------------------------
+
+Figure 1: An FPGA set up with a base image that created three regions. Each
+region gets its own split of the busses that can be independently gated by an
+soft logic bridge in the FPGA. The contents of each PRR can be reprogrammed
+independently while the rest of the system continues to function.
+
+FPGA Bridge
+ * FPGA Bridges gate bus signals between a host and FPGA.
+ * FPGA Bridges should be disabled while the FPGA is being programmed to
+ prevent spurious signals on the cpu bus.
+ * FPGA bridges may be actual hardware or soft logic on the FPGA.
+ * During Full Reconfiguration, hardware bridges between the host and FPGA
+ will be disabled to prevent spurious data on the bus.
+ * These hardware FPGA Bridges may not be needed in implementations where the
+ FPGA Manager transparantly handles gating the buses.
+ * A base FPGA image may create a set of reprogrammable regions, each having
+ its own split of the busses that is gated by its own bridge in the FPGA.
+ * During Partial Reconfiguration of a specific region, the region's bridge
+ will be used to gate the busses. Traffic to other regions is not affected.
+
+Base Image
+ * Also called the "static image"
+ * An FPGA image that is designed to do full reconfiguration of the FPGA.
+ * A base image may set up a set of partial reconfiguration regions that may
+ later be reprogrammed.
+
+
+Overview
+========
+
+This binding introduces the FPGA Region which supports full or partial
+reconfiguration of a FPGA under device tree control.
+
+In the device tree, an FPGA Region brings together the devices (FPGA Managers
+and FPGA Bridges) needed to be able to program an FPGA device. The FPGA Region
+also includes child nodes that are the devices that exist in the FPGA.
+
+The base FPGA Region in the device tree is required to include a phandle to an
+FPGA Manager. This region also contains a list of phandles to the hardware FPGA
+Bridges, if any. This base FPGA Region corresponds to the whole FPGA and is
+used for full reconfiguration.
+
+FPGA Regions that are children of the base FPGA region inherit the parent's FPGA
+Manager but specify their own bridges. These child regions correspond to
+partial reconfiguration regions in the FPGA. The bridges they specify will be
+FPGA Bridges within the static image of the FPGA.
+
+The intended use is that device tree overlays can be used to reprogram an FPGA
+while an operating system is running. In that case, the live device tree will
+contain an FPGA Manager, FPGA Bridges, and the base FPGA Region. The device
+tree overlays contain the name of the FPGA image file to be programmed and the
+child devices that will be contained in the FPGA after programming.
+
+When such a device tree overlay is applied, it is targeted to one of the
+existing FPGA regions. A few things must happen in the OS's implementation
+before the overlay can be accepted into the live tree. The OS will attempt to
+program the FPGA using the firmware that the overlay specifies. That
+reprogramming sequence is detailed below (see the Sequence section). If
+programming fails, the overlay is rejected. If programming succeeds, the
+overlay is added into the live tree and correctly shows what firmware the FPGA
+has been programmed with. Child nodes in the overlay are added and those
+devices are populated.
+
+The base FPGA Region supports full reconfiguration of the FPGA device. If the
+FPGA image loaded contains the logic that creates a set of Partial
+Reconfiguration Regions, then the overlay that programs the FPGA should also add
+a set of FPGA Regions as children of the original FPGA Region. The child FPGA
+Regions do not need to specify an FPGA Manager as they will use the ancestor
+region's FPGA Manager.
+
+
+Constraints
+===========
+
+It is beyond the scope of this document to fully describe all the FPGA design
+constraints required to make partial reconfiguration work[1] [2] [3], but a few
+deserve quick mention.
+
+A persona must have boundary connections that line up with those of the partion
+or region it is designed to go into.
+
+During programming, transactions through those connections must be stopped and
+the connections must be held at a fixed logic level. This can be achieved by
+FPGA Bridges that exist on the FPGA fabric prior to the partial reconfiguration.
+
+FPGA Region
+===========
+
+An FPGA Region specifies the devices (FPGA Manager and FPGA Bridges ) needed to
+reconfigure a FPGA device.
+
+In the live Device Tree, an FPGA Region reflects the current configuration of
+the device. If the live tree shows a "firmware-name" property under a FPGA
+Region, the FPGA already has been programmed with that firmware.
+
+A device tree overlay that targets a FPGA Region and adds the "firmware-name"
+property and child nodes is a request to reprogram the FPGA and, if successful,
+add the child nodes. If reprogramming is not successful, the overlay must be
+rejected and not added to the live tree.
+
+Required properties:
+- compatible : should contain "fpga-region"
+- fpga-mgr : should contain a phandle to an FPGA Manager. Child FPGA
+ Regions inherit this property from the parent, so it
+ should be left out for any child FPGA Regions.
+- fpga-bridges : should contain a list of phandles to FPGA Bridges. This
+ property is optional if the FPGA Manager controls the
+ bridges during reprogramming.
+- #address-cells, #size-cells, ranges: must be present to handle address space
+ mapping for children.
+
+Properties added in an overlay:
+- firmware-name : should contain the name of an FPGA image file located on the
+ firmware search path. If this property shows up in a live device tree it
+ can only mean that the FPGA has already been programmed with this image.
+- partial-fpga-config : boolean property should be defined if partial
+ reconfiguration of the FPGA is to be done, otherwise full reconfiguration
+ is done.
+- external-fpga-config : boolean property should be defined if the FPGA
+ has already been configured. Then the FPGA Region can be used to add
+ child nodes for the devices that are in the FPGA.
+- child nodes : devices in the FPGA after programming.
+
+In the example below, when an overlay is applied targeting base_fpga_region,
+fpgamgr@ff706000 is used to program the FPGA and the bridge specified is
+controlled during the programming. During programming, the bridges listed in
+that region are disabled, the firmware specified in the overlay is loaded to the
+FPGA using the FPGA manager specified in the region. If FPGA programming
+succeeds, the bridges are reenabled and the overlay makes it into the live
+device tree. The jtag_uart and led_pio child devices are then populated. If
+FPGA programming fails, the bridges are left disabled and the overlay is
+rejected.
+
+Example:
+Base tree contains:
+
+ fpga_mgr0: fpgamgr@ff706000 {
+ compatible = "altr,socfpga-fpga-mgr";
+ reg = <0xff706000 0x1000
+ 0xffb90000 0x4>;
+ interrupts = <0 175 4>;
+ };
+
+ fpga_bridge0: fpga_bridge@ff400000 {
+ compatible = "altr,socfpga-lwhps2fpga-bridge";
+ reg = <0xff400000 0x100000>;
+ resets = <&rst LWHPS2FPGA_RESET>;
+ reset-names = "lwhps2fpga";
+ clocks = <&l4_main_clk>;
+ };
+
+ base_fpga_region {
+ compatible = "fpga-region";
+ fpga-mgr = <&fpga_mgr0>;
+ fpga-bridges = <&fpga_bridge0>;
+
+ #address-cells = <0x1>;
+ #size-cells = <0x1>;
+ ranges = <0 0xff200000 0x100000>;
+ };
+
+/dts-v1/ /plugin/;
+/ {
+ fragment@0 {
+ target-path = "/soc/base_fpga_region";
+ #address-cells = <1>;
+ #size-cells = <1>;
+ __overlay__ {
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ firmware-name = "soc_system.rbf";
+
+ jtag_uart: serial@20000 {
+ compatible = "altr,juart-1.0";
+ reg = <0x20000 0x8>;
+ interrupt-parent = <&intc>;
+ interrupts = <0 42 4>;
+ };
+
+ led_pio: gpio@10040 {
+ compatible = "altr,pio-1.0";
+ reg = <0x10040 0x20>;
+ altr,gpio-bank-width = <4>;
+ #gpio-cells = <2>;
+ gpio-controller;
+ };
+ };
+ };
+};
+
+Supported Use Models
+====================
+
+Here's a list of supported use models. We may need to add more. Some uses are
+specific to one FPGA device or another.
+
+In all cases the live DT must specify the FPGA Manager, FPGA Bridges (if any),
+and a FPGA Region. The target of the Device Tree Overlay is the FPGA Region.
+
+ * No FPGA Bridges
+ In this case, the FPGA Manager which programs the FPGA also handles the
+ bridges. No FPGA Bridge devices are needed for full reconfiguration.
+
+ * Full reconfiguration with bridges
+ In this case, there are hardware bridges between the processor and FPGA that
+ need to be disabled during full reconfiguration. Before the overlay is
+ applied, the live DT must include the FPGA Manager, FPGA Bridges, and a
+ base FPGA Region which contains phandles to the FPGA Manager and Bridges.
+
+ * Partial reconfiguration with bridges in the FPGA
+ In this case, the FPGA will have more than one PRR that will be programmed
+ separately. While one PRR is being programmed, other PRR's may be active
+ on the bus. To manage this, FPGA Bridges need to exist in the FPGA
+ that can gate the buses going to one FPGA region while the buses are
+ enabled for other sections. Before any partial reconfiguration can be
+ done, a base FPGA image must be loaded which includes PRR's with FPGA
+ bridges. This can be done by doing full reconfiguration using an overlay
+ that contains the FPGA image that sets up the regions in the FPGA fabric.
+ The overlay would also contain FPGA Regions that will become children of
+ the original base FPGA Region.
+
+Sequence
+========
+
+When a DT overlay is loaded, the FPGA Region will be notified and will do the
+following:
+ 1. Disable the FPGA Bridges.
+ 2. Use the the FPGA manager core to program the FPGA.
+ 3. Enable the FPGA Bridges.
+ 4. Call of_platform_populate resulting in device drivers getting probed.
+
+When the overlay is removed, the FPGA Region will be notified and will disable
+the bridges and the child nodes will be removed.
+
+Device Tree Examples
+====================
+
+The intention of this section is to give some simple examples, focusing on
+the placement of the elements detailed above, especially:
+ * FPGA Manager
+ * FPGA Bridges
+ * FPGA Region
+ * ranges
+ * target-path or target
+
+For the purposes of this section, I'm dividing the Device Tree into two parts,
+each with its own requirements. The two parts are:
+ * The live DT prior to the overlay being added
+ * The DT overlay
+
+The live Device Tree must contain an FPGA Region, an FPGA Manager, and any FPGA
+Bridges. The FPGA Region's "fpga-mgr" property specifies the manager by phandle
+to handle programming the FPGA. If the FPGA Region is the child of another FPGA
+Region, the parent's FPGA Manager is used. If FPGA Bridges need to be involved,
+they are specified in the FPGA Region by the "fpga-bridges" property. During
+FPGA programming, the FPGA Region will disable the bridges that are in its
+"fpga-bridges" list and will re-enable them after FPGA programming has
+succeeded.
+
+The Device Tree Overlay will contain:
+ * "target-path" or "target"
+ The insertion point where the the contents of the overlay will go into the
+ live tree. target-path is a full path, while target is a phandle.
+ * "ranges"
+ The address space mapping from processor to FPGA bus(ses).
+ * "firmware-name"
+ Specifies the name of the FPGA image file on the firmware search
+ path. The search path is described in the firmware class documentation.
+ * "partial-fpga-config"
+ This binding is a boolean and should be present if partial reconfiguration
+ is to be done.
+ * child nodes corresponding to hardware that will be loaded in this region of
+ the FPGA.
+
+Device Tree Example: Full Reconfiguration without Bridges
+=========================================================
+
+Live Device Tree contains:
+ fpga_mgr0: fpgamgr@f8007000 {
+ compatible = "xlnx,zynq-devcfg-1.0";
+ reg = <0xf8007000 0x100>;
+ interrupt-parent = <&intc>;
+ interrupts = <0 8 4>;
+ clocks = <&clkc 12>;
+ clock-names = "ref_clk";
+ syscon = <&slcr>;
+ };
+
+ base_fpga_region {
+ compatible = "fpga-region";
+ fpga-mgr = <&fpga_mgr0>;
+ #address-cells = <0x1>;
+ #size-cells = <0x1>;
+ ranges;
+ };
+
+DT Overlay contains:
+/dts-v1/ /plugin/;
+/ {
+fragment@0 {
+ target = <&base_fpga_region>;
+ #address-cells = <1>;
+ #size-cells = <1>;
+ __overlay__ {
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ firmware-name = "zynq-gpio.bin";
+
+ gpio1: gpio@40000000 {
+ compatible = "xlnx,xps-gpio-1.00.a";
+ reg = <0x40000000 0x10000>;
+ gpio-controller;
+ #gpio-cells = <0x2>;
+ xlnx,gpio-width= <0x6>;
+ };
+ };
+};
+
+Device Tree Example: Full Reconfiguration to add PRR's
+======================================================
+
+The Base FPGA Region is specified similar to the first example above.
+
+This example programs the FPGA to have two regions that can later be partially
+configured. Each region has its own bridge in the FPGA fabric.
+
+DT Overlay contains:
+/dts-v1/ /plugin/;
+/ {
+ fragment@0 {
+ target-path = "/soc/base_fpga_region";
+ #address-cells = <1>;
+ #size-cells = <1>;
+ __overlay__ {
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ firmware-name = "base.rbf";
+
+ fpga_bridge1_0: fpga_bridge@4400 {
+ compatible = "altr,freeze-bridge";
+ reg = <0x4400 0x10>;
+ };
+
+ fpga_bridge2_0: fpga_bridge@4420 {
+ compatible = "altr,freeze-bridge";
+ reg = <0x4420 0x10>;
+ };
+
+ fpga_region1 {
+ compatible = "fpga-region";
+ fpga-bridges = <&fpga_bridge1_0>;
+ #address-cells = <0x1>;
+ #size-cells = <0x1>;
+ ranges;
+ };
+
+ fpga_region2 {
+ compatible = "fpga-region";
+ fpga-bridges = <&fpga_bridge2_0>;
+ #address-cells = <0x1>;
+ #size-cells = <0x1>;
+ ranges;
+ };
+ };
+ };
+};
+
+Device Tree Example: Partial Reconfiguration
+============================================
+
+This example reprograms one of the PRR's set up in the previous example.
+
+The sequence that occurs when this overlay is similar to the above, the only
+differences are that the FPGA is partially reconfigured due to the
+"partial-fpga-config" boolean and the only bridge that is controlled during
+programming is the FPGA based bridge of fpga_region1.
+
+/dts-v1/ /plugin/;
+/ {
+ fragment@0 {
+ target-path = "/soc/base_fpga_region/fpga_region1";
+ #address-cells = <1>;
+ #size-cells = <1>;
+ __overlay__ {
+ #address-cells = <1>;
+ #size-cells = <1>;
+
+ firmware-name = "soc_image2.rbf";
+ partial-fpga-config;
+
+ gpio@10040 {
+ compatible = "altr,pio-1.0";
+ reg = <0x10040 0x20>;
+ clocks = <0x2>;
+ altr,gpio-bank-width = <0x4>;
+ resetvalue = <0x0>;
+ #gpio-cells = <0x2>;
+ gpio-controller;
+ };
+ };
+ };
+};
+
+
+--
+[1] www.altera.com/content/dam/altera-www/global/en_US/pdfs/literature/ug/ug_partrecon.pdf
+[2] tspace.library.utoronto.ca/bitstream/1807/67932/1/Byma_Stuart_A_201411_MAS_thesis.pdf
+[3] http://www.xilinx.com/support/documentation/sw_manuals/xilinx14_1/ug702.pdf
--
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