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

Rob Herring
2022-03-31T17:21:52Z

On Thu, Mar 31, 2022 at 06:13:53PM +0200, Martin Povišer wrote:
>
> > On 31. 3. 2022, at 16:10, Vinod Koul <vkoul@kernel.org> wrote:
> >
> > On 31-03-22, 09:06, Martin Povišer wrote:
> >>
> >>> On 31. 3. 2022, at 8:50, Martin Povišer <povik@cutebit.org> wrote:
> >>>>
> >>>> On 31. 3. 2022, at 7:23, Vinod Koul <vkoul@kernel.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@cutebit.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