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-FPGA Region Device Tree Binding
-
-Alan Tull 2016
-
- CONTENTS
- - Introduction
- - Terminology
- - Sequence
- - FPGA Region
- - Supported Use Models
- - Device Tree Examples
- - Constraints
-
-
-Introduction
-============
-
-FPGA Regions represent FPGA's and partial reconfiguration regions of FPGA's in
-the Device Tree. FPGA Regions provide a way to program FPGAs under device tree
-control.
-
-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 specifications for FPGA
-usage.
-
-
-Terminology
-===========
-
-Full Reconfiguration
- * The entire FPGA is programmed.
-
-Partial Reconfiguration (PR)
- * A section of an FPGA is reprogrammed while the rest of the FPGA is not
- affected.
- * Not all FPGA's support PR.
-
-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 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 and to the soft logic.
- * FPGA bridges may be actual hardware or soft logic on an FPGA.
- * During Full Reconfiguration, hardware bridges between the host and FPGA
- will be disabled.
- * During Partial Reconfiguration of a specific region, that region's bridge
- will be used to gate the busses. Traffic to other regions is not affected.
- * In some implementations, the FPGA Manager transparantly handles gating the
- buses, eliminating the need to show the hardware FPGA bridges in the
- device tree.
- * An FPGA image may create a set of reprogrammable regions, each having its
- own bridge and its own split of the busses in the FPGA.
-
-FPGA Manager
- * An FPGA Manager is a hardware block that programs an FPGA under the control
- of a host processor.
-
-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.
-
- ---------------- ----------------------------------
- | Host CPU | | FPGA |
- | | | |
- | ----| | ----------- -------- |
- | | H | | |==>| Bridge0 |<==>| PRR0 | |
- | | W | | | ----------- -------- |
- | | | | | |
- | | B |<=====>|<==| ----------- -------- |
- | | R | | |==>| Bridge1 |<==>| PRR1 | |
- | | I | | | ----------- -------- |
- | | D | | | |
- | | G | | | ----------- -------- |
- | | E | | |==>| Bridge2 |<==>| PRR2 | |
- | ----| | ----------- -------- |
- | | | |
- ---------------- ----------------------------------
-
-Figure 1: An FPGA set up with a base image that created three regions. Each
-region (PRR0-2) gets its own split of the busses that is independently gated by
-a soft logic bridge (Bridge0-2) in the FPGA. The contents of each PRR can be
-reprogrammed independently while the rest of the system continues to function.
-
-
-Sequence
-========
-
-When a DT overlay that targets a FPGA Region is applied, the FPGA Region will
-do the following:
-
- 1. Disable appropriate FPGA bridges.
- 2. Program the FPGA using the FPGA manager.
- 3. Enable the FPGA bridges.
- 4. The Device Tree overlay is accepted into the live tree.
- 5. Child devices are populated.
-
-When the overlay is removed, the child nodes will be removed and the FPGA Region
-will disable the bridges.
-
-
-FPGA Region
-===========
-
-FPGA Regions represent FPGA's and FPGA PR regions in the device tree. An FPGA
-Region brings together the elements needed to program on a running system and
-add the child devices:
-
- * FPGA Manager
- * FPGA Bridges
- * image-specific information needed to to the programming.
- * child nodes
-
-The intended use is that a Device Tree overlay (DTO) can be used to reprogram an
-FPGA while an operating system is running.
-
-An FPGA Region that exists in the live Device Tree reflects the current state.
-If the live tree shows a "firmware-name" property or child nodes under a FPGA
-Region, the FPGA already has been programmed. A DTO that targets a FPGA Region
-and adds the "firmware-name" property is taken as a request to reprogram the
-FPGA. After reprogramming is successful, the overlay is accepted into the live
-tree.
-
-The base FPGA Region in the device tree represents the FPGA and supports full
-reconfiguration. It must include a phandle to an FPGA Manager. The base
-FPGA region will be the child of one of the hardware bridges (the bridge that
-allows register access) between the cpu and the FPGA. If there are more than
-one bridge to control during FPGA programming, the region will also contain a
-list of phandles to the additional hardware FPGA Bridges.
-
-For partial reconfiguration (PR), each PR region will have an FPGA Region.
-These FPGA regions are children of FPGA bridges which are then children of the
-base FPGA region. The "Full Reconfiguration to add PRR's" example below shows
-this.
-
-If an FPGA Region does not specify a FPGA Manager, it will inherit the FPGA
-Manager specified by its ancestor FPGA Region. This supports both the case
-where the same FPGA Manager is used for all of a FPGA as well the case where
-a different FPGA Manager is used for each region.
-
-FPGA Regions do not inherit their ancestor FPGA regions' bridges. This prevents
-shutting down bridges that are upstream from the other active regions while one
-region is getting reconfigured (see Figure 1 above). During PR, the FPGA's
-hardware bridges remain enabled. The PR regions' bridges will be FPGA bridges
-within the static image of the FPGA.
-
-Required properties:
-- compatible : should contain "fpga-region"
-- fpga-mgr : should contain a phandle to an FPGA Manager. Child FPGA Regions
- inherit this property from their ancestor regions. A fpga-mgr property
- in a region will override any inherited FPGA manager.
-- #address-cells, #size-cells, ranges : must be present to handle address space
- mapping for child nodes.
-
-Optional properties:
-- 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 indicates that the FPGA has already been programmed with this image.
- If this property is in an overlay targeting a FPGA region, it is a
- request to program the FPGA with that image.
-- fpga-bridges : should contain a list of phandles to FPGA Bridges that must be
- controlled during FPGA programming along with the parent FPGA bridge.
- This property is optional if the FPGA Manager handles the bridges.
- If the fpga-region is the child of a fpga-bridge, the list should not
- contain the parent bridge.
-- partial-fpga-config : boolean, set if partial reconfiguration is to be done,
- otherwise full reconfiguration is done.
-- external-fpga-config : boolean, set if the FPGA has already been configured
- prior to OS boot up.
-- encrypted-fpga-config : boolean, set if the bitstream is encrypted
-- region-unfreeze-timeout-us : The maximum time in microseconds to wait for
- bridges to successfully become enabled after the region has been
- programmed.
-- region-freeze-timeout-us : The maximum time in microseconds to wait for
- bridges to successfully become disabled before the region has been
- programmed.
-- config-complete-timeout-us : The maximum time in microseconds time for the
- FPGA to go to operating mode after the region has been programmed.
-- child nodes : devices in the FPGA after programming.
-
-In the example below, when an overlay is applied targeting fpga-region0,
-fpga_mgr is used to program the FPGA. Two bridges are controlled during
-programming: the parent fpga_bridge0 and fpga_bridge1. Because the region is
-the child of fpga_bridge0, only fpga_bridge1 needs to be specified in the
-fpga-bridges property. During programming, these bridges 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 child devices
-are then populated. If FPGA programming fails, the bridges are left disabled
-and the overlay is rejected. The overlay's ranges property maps the lwhps
-bridge's region (0xff200000) and the hps bridge's region (0xc0000000) for use by
-the two child devices.
-
-Example:
-Base tree contains:
-
- fpga_mgr: fpga-mgr@ff706000 {
- compatible = "altr,socfpga-fpga-mgr";
- reg = <0xff706000 0x1000
- 0xffb90000 0x20>;
- interrupts = <0 175 4>;
- };
-
- fpga_bridge0: fpga-bridge@ff400000 {
- compatible = "altr,socfpga-lwhps2fpga-bridge";
- reg = <0xff400000 0x100000>;
- resets = <&rst LWHPS2FPGA_RESET>;
- clocks = <&l4_main_clk>;
-
- #address-cells = <1>;
- #size-cells = <1>;
- ranges;
-
- fpga_region0: fpga-region0 {
- compatible = "fpga-region";
- fpga-mgr = <&fpga_mgr>;
- };
- };
-
- fpga_bridge1: fpga-bridge@ff500000 {
- compatible = "altr,socfpga-hps2fpga-bridge";
- reg = <0xff500000 0x10000>;
- resets = <&rst HPS2FPGA_RESET>;
- clocks = <&l4_main_clk>;
- };
-
-Overlay contains:
-
-/dts-v1/ /plugin/;
-/ {
- fragment@0 {
- target = <&fpga_region0>;
- #address-cells = <1>;
- #size-cells = <1>;
- __overlay__ {
- #address-cells = <1>;
- #size-cells = <1>;
-
- firmware-name = "soc_system.rbf";
- fpga-bridges = <&fpga_bridge1>;
- ranges = <0x20000 0xff200000 0x100000>,
- <0x0 0xc0000000 0x20000000>;
-
- gpio@10040 {
- compatible = "altr,pio-1.0";
- reg = <0x10040 0x20>;
- altr,gpio-bank-width = <4>;
- #gpio-cells = <2>;
- clocks = <2>;
- gpio-controller;
- };
-
- onchip-memory {
- device_type = "memory";
- compatible = "altr,onchipmem-15.1";
- reg = <0x0 0x10000>;
- };
- };
- };
-};
-
-
-Supported Use Models
-====================
-
-In all cases the live DT must have the FPGA Manager, FPGA Bridges (if any), and
-a FPGA Region. The target of the Device Tree Overlay is the FPGA Region. Some
-uses are specific to a FPGA device.
-
- * No FPGA Bridges
- In this case, the FPGA Manager which programs the FPGA also handles the
- bridges behind the scenes. No FPGA Bridge devices are needed for full
- reconfiguration.
-
- * Full reconfiguration with hardware bridges
- In this case, there are hardware bridges between the processor and FPGA that
- need to be controlled during full reconfiguration. Before the overlay is
- applied, the live DT must include the FPGA Manager, FPGA Bridges, and a
- FPGA Region. The FPGA Region is the child of the bridge that allows
- register access to the FPGA. Additional bridges may be listed in a
- fpga-bridges property in the FPGA region or in the device tree overlay.
-
- * Partial reconfiguration with bridges in the FPGA
- In this case, the FPGA will have one or more PRR's that may be programmed
- separately while the rest of the FPGA can remain active. To manage this,
- bridges need to exist in the FPGA that can gate the buses going to each 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. The device tree should have a FPGA region for each
- PRR.
-
-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: fpga-mgr@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>;
- };
-
- fpga_region0: fpga-region0 {
- compatible = "fpga-region";
- fpga-mgr = <&fpga_mgr0>;
- #address-cells = <0x1>;
- #size-cells = <0x1>;
- ranges;
- };
-
-DT Overlay contains:
-/dts-v1/ /plugin/;
-/ {
-fragment@0 {
- target = <&fpga_region0>;
- #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 = <&fpga_region0>;
- #address-cells = <1>;
- #size-cells = <1>;
- __overlay__ {
- #address-cells = <1>;
- #size-cells = <1>;
-
- firmware-name = "base.rbf";
-
- fpga-bridge@4400 {
- compatible = "altr,freeze-bridge-controller";
- reg = <0x4400 0x10>;
-
- fpga_region1: fpga-region1 {
- compatible = "fpga-region";
- #address-cells = <0x1>;
- #size-cells = <0x1>;
- ranges;
- };
- };
-
- fpga-bridge@4420 {
- compatible = "altr,freeze-bridge-controller";
- reg = <0x4420 0x10>;
-
- fpga_region2: fpga-region2 {
- compatible = "fpga-region";
- #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 = <&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;
- };
- };
- };
-};
-
-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.
-
---
-[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
generated by cgit (git 2.34.1) at 2024-05-09 20:03:36 +0000