linux-kernel - Re: [PATCH v12 2/6] fpga: add bindings document for simple fpga bus

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Date:	Wed, 28 Oct 2015 10:40:02 +0100
From:	Steffen Trumtrar <s.trumtrar@...gutronix.de>
To:	atull@...nsource.altera.com
Cc:	gregkh@...uxfoundation.org,
	Moritz Fischer <moritz.fischer@...us.com>,
	Josh Cartwright <joshc@...com>, monstr@...str.eu,
	michal.simek@...inx.com, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	pantelis.antoniou@...sulko.com, delicious.quinoa@...il.com,
	dinguyen@...nsource.altera.com
Subject: Re: [PATCH v12 2/6] fpga: add bindings document for simple fpga bus

On Tue, Oct 27, 2015 at 05:09:11PM -0500, atull@...nsource.altera.com wrote:
> From: Alan Tull <atull@...nsource.altera.com>
> 
> New bindings document for simple fpga bus.
> 
> Signed-off-by: Alan Tull <atull@...nsource.altera.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.
> ---
>  .../devicetree/bindings/fpga/simple-fpga-bus.txt   |   81 ++++++++++++++++++++
>  1 file changed, 81 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/fpga/simple-fpga-bus.txt
> 
> diff --git a/Documentation/devicetree/bindings/fpga/simple-fpga-bus.txt b/Documentation/devicetree/bindings/fpga/simple-fpga-bus.txt
> new file mode 100644
> index 0000000..2e742f7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/fpga/simple-fpga-bus.txt
> @@ -0,0 +1,81 @@
> +Simple FPGA Bus
> +===============
> +
> +A Simple FPGA Bus is a bus that handles configuring an FPGA and its bridges
> +before populating the devices below its node.  All this happens when a device
> +tree overlay is added to the live tree.  This document describes that device
> +tree overlay.
> +
> +Required properties:
> +- compatible : should contain "simple-fpga-bus"
> +- #address-cells, #size-cells, ranges: must be present to handle address space
> +  mapping for children.
> +
> +Optional properties:
> +- fpga-mgr : should contain a phandle to a FPGA manager.
> +- fpga-firmware : should contain the name of a FPGA image file located on the
> +  firmware search path.
> +- partial-reconfig : boolean property should be defined if partial
> +  reconfiguration of the FPGA is to be done, otherwise full reconfiguration
> +  is done.
> +- fpga-bridges : should contain a list of bridges that the bus will disable
> +  before   programming the FPGA and then enable after the FPGA has been
> +
> +Example:
> +
> +/dts-v1/;
> +/plugin/;
> +/ {
> +	fragment@0 {
> +		target-path="/soc";
> +		__overlay__ {
> +			#address-cells = <1>;
> +	                #size-cells = <1>;
> +
> +			bridge@...f200000 {
> +				compatible = "simple-fpga-bus";
> +				reg = <0xc0000000 0x20000000>,
> +				      <0xff200000 0x00200000>;
> +				reg-names = "axi_h2f", "axi_h2f_lw";
> +
> +				#address-cells = <0x2>;
> +				#size-cells = <0x1>;
> +
> +				ranges = <0x00000000 0x00000000 0xc0000000 0x00010000>,
> +					 <0x00000001 0x00020000 0xff220000 0x00000008>,
> +					 <0x00000001 0x00010040 0xff210040 0x00000020>;
> +
> +				clocks = <0x2 0x2>;
> +				clock-names = "h2f_lw_axi_clock", "f2h_sdram0_clock";
> +
> +				fpga-mgr = <&hps_0_fpgamgr>;
> +				fpga-firmware = "soc_system.rbf";
> +
> +				fpga-bridges = <&hps_fpgabridge0>, <&hps_fpgabridge1>, <&hps_fpgabridge2>;

At least for Socfpga the HPS2FPGA and FPGA2HPS bridges can be configured to have
a bus width of 32, 64, 128 depending on the bitstream. How does this fit into here?
For DMA over this bus this is an interesting property to know, isn't it?
I guess something like "<&hps_fpgabridge0 64>" could be a possible solution, but
what is with the GPV registers of the bridges? Do they depend on the bitstream
loaded? Then this would get really messy I guess as it not a generic property.

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