From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx> Add a document spelling out usage of the simple fpga bus. Signed-off-by: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx> Reviewed-by: Moritz Fischer <moritz.fischer@xxxxxxxxx> --- v9: Initial version of this patch in patchset v10: s/fpga/FPGA/g improve formatting some rewriting move to staging/simple-fpga-bus v11: No change in this patch for v11 of the patch set v12: Moved out of staging Small changes due to using FPGA bridge framework and not representing the bridges as resets. v13: Fix some nits --- Documentation/fpga/simple-fpga-bus.txt | 58 ++++++++++++++++++++++++++++++++++ 1 file changed, 58 insertions(+) create mode 100644 Documentation/fpga/simple-fpga-bus.txt diff --git a/Documentation/fpga/simple-fpga-bus.txt b/Documentation/fpga/simple-fpga-bus.txt new file mode 100644 index 0000000..9b04826 --- /dev/null +++ b/Documentation/fpga/simple-fpga-bus.txt @@ -0,0 +1,58 @@ +Simple FPGA Bus + +Alan Tull 2015 + +Overview +======== + +The simple FPGA bus adds device tree overlay support for FPGAs. Loading a DT +overlay will result in the FPGA getting programmed with an image, its bridges +will be released, and the DT populated for nodes below the simple-fpga-bus. +This results in drivers getting probed for the hardware that just got added. +This is intended to support the FPGA usage where the FPGA has hardware that +requires drivers. Removing the overlay will result in the drivers getting +removed and the bridges being disabled. + +The simple FPGA bus will need to disable and enable bridges that will only +affect the child devices that are below the bus. If partial reconfiguration +is to be done, then bridges will need to be added within the FPGA design to +protect the rest of the bus when one part of the FPGA design is being +reconfigured. + + +Sequence +======== + +Load the DT overlay. One way to do that from user space is to use Pantelis' +DT-Overlay configfs interface. + +This causes the simple FPGA bus to be probed and will do the following: + 1. Disable the FPGA bridges. + 2. Call the FPGA manager core to program the FPGA. + 3. Release the FPGA bridges. + 4. Call of_platform_populate resulting in device drivers getting probed. + + +Requirements +============ + + 1. An FPGA image that has a hardware block or blocks that use drivers that are + supported in the kernel. + 2. A device tree overlay (example is in the simple-fpga-bus bindings document). + 3. A FPGA manager driver supporting writing the FPGA. + 4. FPGA bridge drivers. + +The DT overlay includes bindings (documented in bindings/simple-fpga-bus.txt) +that specify: + * Which FPGA manager to use. + * Which image file to load. + * Flags indicating whether this this image is for full reconfiguration or + partial. + * A list of FPGA bridges. + * Child nodes specifying the devices that will be added with appropriate + compatible strings, etc. + +Since this code uses the firmware interface to get the image and DT overlay, +they currently have to be files on the file system. It doesn't have to be that +way forever as DT bindings could be added to point to other sources for the +image. -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html