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

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Message-ID: <6f305564-e91c-794b-0025-de805f1d1a58@microchip.com>
Date:   Fri, 16 Oct 2020 06:45:51 +0000
From:   <Eugen.Hristev@...rochip.com>
To:     <robh@...nel.org>
CC:     <vkoul@...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 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.

Eugen