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diff --git a/Documentation/devicetree/bindings/fpga/fpga-region.txt b/Documentation/devicetree/bindings/fpga/fpga-region.txt new file mode 100644 index 000000000..6694ef29a --- /dev/null +++ b/Documentation/devicetree/bindings/fpga/fpga-region.txt @@ -0,0 +1,479 @@ +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 an 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 an 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 an FPGA +Region, the FPGA already has been programmed. A DTO that targets an 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 an 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 an 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. An 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 an 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 an 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/; + +&fpga_region0 { + #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,ngpio = <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 an 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 an 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 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/; + +&fpga_region0 { + #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/; + +&fpga_region0 { + #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/; + +&fpga_region1 { + #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,ngpio = <0x4>; + #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] https://www.xilinx.com/support/documentation/sw_manuals/xilinx14_1/ug702.pdf |