linux-kernel - Re: [PATCH 6/7] dt-bindings: dmaengine: at_xdmac: add optional microchip,m2m property

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Date:   Fri, 16 Oct 2020 07:09:12 +0000
From:   <Eugen.Hristev@...rochip.com>
To:     <vkoul@...nel.org>
CC:     <robh@...nel.org>, <Tudor.Ambarus@...rochip.com>,
        <Ludovic.Desroches@...rochip.com>, <dmaengine@...r.kernel.org>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <Nicolas.Ferre@...rochip.com>
Subject: Re: [PATCH 6/7] dt-bindings: dmaengine: at_xdmac: add optional
 microchip,m2m property

On 16.10.2020 10:06, Vinod Koul wrote:
> Hi Eugen,
> 
> On 16-10-20, 06:45, Eugen.Hristev@...rochip.com wrote:
>> On 23.09.2020 02:33, Rob Herring wrote:
>>
>>> On Mon, Sep 14, 2020 at 05:09:55PM +0300, Eugen Hristev wrote:
>>>> Add optional microchip,m2m property that specifies if a controller is
>>>> dedicated to memory to memory operations only.
>>>>
>>>> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
>>>> ---
>>>>    Documentation/devicetree/bindings/dma/atmel-xdma.txt | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/dma/atmel-xdma.txt b/Documentation/devicetree/bindings/dma/atmel-xdma.txt
>>>> index 510b7f25ba24..642da6b95a29 100644
>>>> --- a/Documentation/devicetree/bindings/dma/atmel-xdma.txt
>>>> +++ b/Documentation/devicetree/bindings/dma/atmel-xdma.txt
>>>> @@ -15,6 +15,12 @@ the dmas property of client devices.
>>>>        interface identifier,
>>>>        - bit 30-24: PERID, peripheral identifier.
>>>>
>>>> +Optional properties:
>>>> +- microchip,m2m: this controller is connected on AXI only to memory and it's
>>>> +     dedicated to memory to memory DMA operations. If this option is
>>>> +     missing, it's assumed that the DMA controller is connected to
>>>> +     peripherals, thus it's a per2mem and mem2per.
>>>
>>> Wouldn't 'dma-requests = <0>' cover this case?
>>>
>>> Rob
>>>
>>
>> Hi Rob,
>>
>> I do not think so. With requests = 0, it means that actually the DMA
>> controller is unusable ?
>> Since you suggest requests = 0, it means that it cannot take requests at
>> all ?
>> I do not find another example in current DT with this property set to zero.
> 
> Not really, dma-requests implies "request signals supported" which are
> used for peripheral cases. m2m does not need request signals, so it is
> very reasonable to conclude that dma-requests = <0> would imply no
> peripheral support and only m2m support.

Thanks for explaining, I will change accordingly then.

Eugen

> 
> Thanks
> --
> ~Vinod
>