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

[Rob Herring]

On Fri, Apr 22, 2016 at 12:36 AM, Appana Durga Kedareswara Rao
<appana.durga.rao@xxxxxxxxxx> wrote:
> Hi Rob,
>
>         Thanks for the review...
>
>> -----Original Message-----
>> From: Rob Herring [mailto:robh@xxxxxxxxxx]
>> Sent: Thursday, April 21, 2016 7:12 PM
>> To: Appana Durga Kedareswara Rao <appanad@xxxxxxxxxx>
>> Cc: pawel.moll@xxxxxxx; mark.rutland@xxxxxxx;
>> ijc+devicetree@xxxxxxxxxxxxxx; galak@xxxxxxxxxxxxxx; Michal Simek
>> <michals@xxxxxxxxxx>; Soren Brinkmann <sorenb@xxxxxxxxxx>;
>> vinod.koul@xxxxxxxxx; dan.j.williams@xxxxxxxxx; Appana Durga Kedareswara
>> Rao <appanad@xxxxxxxxxx>; moritz.fischer@xxxxxxxxx;
>> laurent.pinchart@xxxxxxxxxxxxxxxx; luis@xxxxxxxxxxxxxxxxx; Anirudha
>> Sarangi <anirudh@xxxxxxxxxx>; Punnaiah Choudary Kalluri
>> <punnaia@xxxxxxxxxx>; devicetree@xxxxxxxxxxxxxxx; linux-arm-
>> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>> dmaengine@xxxxxxxxxxxxxxx
>> 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@xxxxxxxxxx>
>> > Signed-off-by: Kedareswara rao Appana <appanad@xxxxxxxxxx>
>> > ---
>> > 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.
>
>
> The DMA supports an AXI bus width of 128/64 bits only.
> Please refer IP data sheet. http://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf Page No: 359(DMA Over fetch section).

I understand that. That should not really matter if the AXI master
properly sets byte lane strobes other than defining max burst length
which you already have defined elsewhere.

> That's why during probe we are making the dma_device supported source and destination address widths accordingly based on the DT property.
>
> Snap shot of driver code from the probe:
>        struct dma_device *p;
>        p->dst_addr_widths = zdev->chan->bus_width / 8;
>        p->src_addr_widths = zdev->chan->bus_width / 8;

Read what I wrote before and read the documentation for these fields.
They are bitmasks.

Rob