linux-kernel - Re: [PATCH v1] dt-bindings: dma: st-stm32-dmamux: Add description for dma-cell values

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Message-ID: <bdfeceb6-962a-4f20-b76c-4fe5e5ff80c3@foss.st.com>
Date: Thu, 5 Dec 2024 19:04:39 +0100
From: Amelie Delaunay <amelie.delaunay@...s.st.com>
To: Krzysztof Kozlowski <krzk@...nel.org>,
        Ken Sloat
	<ksloat@...nersoftsolutions.com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <dmaengine@...r.kernel.org>, <alexandre.torgue@...s.st.com>,
        <mcoquelin.stm32@...il.com>, <conor+dt@...nel.org>,
        <krzk+dt@...nel.org>, <robh@...nel.org>, <vkoul@...nel.org>
Subject: Re: [PATCH v1] dt-bindings: dma: st-stm32-dmamux: Add description for
 dma-cell values


On 12/5/24 17:09, Krzysztof Kozlowski wrote:
> On 05/12/2024 17:07, Ken Sloat wrote:
>>>> + 1. The mux input number/line for the request
>>>> + 2. Bitfield representing DMA channel configuration that is passed
>>>> + to the real DMA controller
>>>> + 3. Bitfield representing device dependent DMA features passed to
>>>> + the real DMA controller
>>>> +
>>>> + For bitfield definitions of cells 2 and 3, see the associated
>>>> + bindings doc for the actual DMA controller the mux is connected
>>>
>>> This does not sound right. This is the binding for DMA controller, so
>>> you are saying "please look at itself". I suggest to drop this as well.
>>>
>>
>> While logically it is the DMA controller, this doc is specifically for
>> the mux - the DMA controller has its own driver and binding docs in
>> Documentation/devicetree/bindings/dma/stm32/st,stm32-dma.yaml
>>
>> I can reference st,stm32-dma.yaml directly, but I was unsure if this
>> mux IP was used with another DMA controller from ST on a different
>> SoC.
>>
>> What do you suggest here?
> 
> Thanks for explanation, I think it is fine.
> 
> Best regards,
> Krzysztof

This description was lost when STM32 DMAMUX binding txt file was 
converted to yaml:
0b7c446fa9f7 ("dt-bindings: dma: Convert stm32 DMAMUX bindings to 
json-schema")

-- #dma-cells:	Should be set to <3>.
-		First parameter is request line number.
-		Second is DMA channel configuration
-		Third is Fifo threshold
-		For more details about the three cells, please see
-		stm32-dma.txt documentation binding file


stm32-dmamux exclusively muxes stm32-dma channels. It is not used with 
other ST DMA controllers (STM32 MDMA, STM32 DMA3).

So it is fine to refer to st,stm32-dma.yaml.

Regards,
Amelie