linux-kernel - Re: [PATCH v6 1/2] Documentation: DT: dma: Add Xilinx zynqmp dma device tree binding documentation

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Date:	Thu, 21 Apr 2016 08:42:26 -0500
From:	Rob Herring <robh@...nel.org>
To:	Kedareswara rao Appana <appana.durga.rao@...inx.com>
Cc:	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	michal.simek@...inx.com, soren.brinkmann@...inx.com,
	vinod.koul@...el.com, dan.j.williams@...el.com, appanad@...inx.com,
	moritz.fischer@...us.com, laurent.pinchart@...asonboard.com,
	luis@...ethencourt.com, anirudh@...inx.com, punnaia@...inx.com,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH v6 1/2] Documentation: DT: dma: Add Xilinx zynqmp dma
 device tree binding documentation

On Fri, Apr 15, 2016 at 02:22:53PM +0530, Kedareswara rao Appana wrote:
> Device-tree binding documentation for Xilinx zynqmp dma engine used in
> Zynq UltraScale+ MPSoC.
> 
> Signed-off-by: Punnaiah Choudary Kalluri <punnaia@...inx.com>
> Signed-off-by: Kedareswara rao Appana <appanad@...inx.com>
> ---
> Changes in v6:
> - Removed desc-axi-cache/dst-axi-cache/src-axi-cache properties
>   from the binding doc as it allow broken combinations when dma-coherent
>   is set as suggested by Rob.
> - Fixed minor comments given by Rob related coding(lower case DT node name).
> Changes in v5:
> - Use dma-coherent flag for coherent transfers as suggested by rob.
> - Removed unnecessary properties from binding doc as suggested by Rob.
> Changes in v4:
> - None
> Changes in v3:
> - None
> Changes in v2:
> - None.
> 
>  .../devicetree/bindings/dma/xilinx/zynqmp_dma.txt  | 44 ++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/dma/xilinx/zynqmp_dma.txt
> 
> diff --git a/Documentation/devicetree/bindings/dma/xilinx/zynqmp_dma.txt b/Documentation/devicetree/bindings/dma/xilinx/zynqmp_dma.txt
> new file mode 100644
> index 0000000..f0f0b54
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/xilinx/zynqmp_dma.txt
> @@ -0,0 +1,44 @@
> +Xilinx ZynqMP DMA engine, it does support memory to memory transfers,
> +memory to device and device to memory transfers. It also has flow
> +control and rate control support for slave/peripheral dma access.
> +
> +Required properties:
> +- compatible		: Should be "xlnx,zynqmp-dma-1.0"
> +- reg			: Memory map for gdma/adma module access.
> +- interrupt-parent	: Interrupt controller the interrupt is routed through
> +- interrupts		: Should contain DMA channel interrupt.
> +- xlnx,bus-width	: Axi buswidth in bits. Should contain 128 or 64

I think how this is getting used by the driver is wrong. 
{src,dst}_addr_widths are supposed to be a bitmask of supported slave 
device register widths. You aren't doing a bitmask and you are also 
saying you only support slaves with 8 or 16 byte data registers which is 
somewhat rare. It may happen to work because 128/8 == BIT(4). However, 
the documentation for the field is contradictory in that it says 1,2,4 
or 8 byte widths are supported, but the enum has more sizes.

Rob