[PATCH v13 1/6] fpga: add usage documentation for simple fpga bus

From: atull
Date: Tue Nov 03 2015 - 12:19:02 EST

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
+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
+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.
+ 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

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