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

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Message-ID: <YkXjJ2gtX4sL000U@robh.at.kernel.org>
Date:   Thu, 31 Mar 2022 12:21:43 -0500
From:   Rob Herring <robh@...nel.org>
To:     Martin Povišer <povik@...ebit.org>
Cc:     Vinod Koul <vkoul@...nel.org>,
        Martin Povišer <povik+lin@...ebit.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>,
        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 Thu, Mar 31, 2022 at 06:13:53PM +0200, Martin Povišer wrote:
> 
> > 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.

Why do they have to be different? IRQF_SHARED doesn't work?

Why can't you request each IRQ until it succeeds?

What happens when there are 5 DMA controllers?

If using more than 1 interrupt will never work or be needed, then I'm 
inclined to say just describe that 1 interrupt. Yes, that goes against 
'describe all the h/w', but there's always exceptions. I suppose you 
need to know which 'interrupts' index (output) you are using. If so, you 
can do something like this:

interrupts = <-1>, <-1>, <3 0>, <-1>;

Rob