linux-kernel - Re: [PATCH 1/2] dt-bindings: dma: Add Apple ADMAC

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Date:   Thu, 31 Mar 2022 18:13:53 +0200
From:   Martin Povišer <povik@...ebit.org>
To:     Vinod Koul <vkoul@...nel.org>
Cc:     Martin Povišer <povik+lin@...ebit.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        linux-arm-kernel@...ts.infradead.org, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mark Kettenis <kettenis@...nbsd.org>
Subject: Re: [PATCH 1/2] dt-bindings: dma: Add Apple ADMAC


> On 31. 3. 2022, at 16:10, Vinod Koul <vkoul@...nel.org> wrote:
> 
> On 31-03-22, 09:06, Martin Povišer wrote:
>> 
>>> On 31. 3. 2022, at 8:50, Martin Povišer <povik@...ebit.org> wrote:
>>>> 
>>>> On 31. 3. 2022, at 7:23, Vinod Koul <vkoul@...nel.org> wrote:
>>>> 
>>>> On 30-03-22, 18:44, Martin Povišer wrote:
>>>>> Apple's Audio DMA Controller (ADMAC) is used to fetch and store audio
>>>>> samples on Apple SoCs from the "Apple Silicon" family.
>>>>> 
>>>>> Signed-off-by: Martin Povišer <povik+lin@...ebit.org>
>>>>> ---
>>>>> .../devicetree/bindings/dma/apple,admac.yaml  | 73 +++++++++++++++++++
>>>>> 1 file changed, 73 insertions(+)
>>>>> create mode 100644 Documentation/devicetree/bindings/dma/apple,admac.yaml
>>>>> 
>>>>> diff --git a/Documentation/devicetree/bindings/dma/apple,admac.yaml b/Documentation/devicetree/bindings/dma/apple,admac.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..34f76a9a2983
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/dma/apple,admac.yaml
>>> 
>>>>> +  apple,internal-irq-destination:
>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>> +    description: Index influencing internal routing of the IRQs
>>>>> +      within the peripheral.
>>>> 
>>>> do you have more details for this, is this for peripheral and if so
>>>> suited to be in dam-cells?
>>> 
>>> By peripheral I meant the DMA controller itself here. 
> 
> Dmaengine convention is that peripheral is device which we are doing dma
> to/from, like audio controller/fifo here
> 
>>> Effectively the controller has four independent IRQ outputs and the driver
>>> needs to know which one we are using. (It need not be the same output even
>>> for different ADMAC instances on one die.)
> 
> That smells like a mux to me.. why not use dma-requests for this?

I am not sure that’s right. Reading the dmaengine docs, DMA requests seem to have
to do with the DMA-controller-to-peripheral connection, but the proposed property
tells us which of four independent IRQ outputs of the DMA controller we actually
have in the interrupts= property. That is, it has to do with the DMA-controller-to-CPU
connection.

(I took the liberty of correcting my typo in the quotation.)

> 
> -- 
> ~Vinod