linux-kernel - Re: [PATCH v2 1/2] dt-bindings: dma: Add Apple ADMAC

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Date:   Thu, 14 Apr 2022 19:23:38 +0200
From:   Martin Povišer <povik@...ebit.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Martin Povišer <povik+lin@...ebit.org>,
        Hector Martin <marcan@...can.st>,
        Sven Peter <sven@...npeter.dev>, Vinod Koul <vkoul@...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 v2 1/2] dt-bindings: dma: Add Apple ADMAC


> On 14. 4. 2022, at 17:43, Rob Herring <robh@...nel.org> wrote:
> 
> On Tue, Apr 12, 2022 at 12:22:03AM +0200, Martin Povišer wrote:
>> Apple's Audio DMA Controller (ADMAC) is used to fetch and store audio
>> samples on SoCs from the "Apple Silicon" family.
>> 
>> Signed-off-by: Martin Povišer <povik+lin@...ebit.org>
>> ---
>> 
>> After the v1 discussion, I dropped the apple,internal-irq-destination
>> property and instead the index of the usable interrupt is now signified
>> by prepending -1 entries to the interrupts= list. This works when I do
>> it like this:
>> 
>>  interrupt-parent = <&aic>;
>>  interrupts = <AIC_IRQ 0xffffffff 0>,
>>               <AIC_IRQ 626 IRQ_TYPE_LEVEL_HIGH>;
> 
> 
> BTW, just use '-1'. dtc takes negative values (and other expressions).

Ha! <-1> didn’t work for me but <(-1)> does.

> 
>> 
>> I would find it neat to do it like this:
>> 
>>  interrupts-extended = <0xffffffff>,
>>                        <&aic AIC_IRQ 626 IRQ_TYPE_LEVEL_HIGH>;
>> 
>> but unfortunately the kernel doesn't pick up on it:
>> 
>> [    0.767964] apple-admac 238200000.dma-controller: error -6: IRQ index 0 not found
>> [    0.773943] apple-admac 238200000.dma-controller: error -6: IRQ index 1 not found
>> [    0.780154] apple-admac 238200000.dma-controller: error -6: IRQ index 2 not found
>> [    0.786367] apple-admac 238200000.dma-controller: error -6: IRQ index 3 not found
>> [    0.788592] apple-admac 238200000.dma-controller: error -6: no usable interrupt
> 
> We should make this case work. It is less fragile IMO as it doesn't 
> depend on the provider's translation of cells.

Then I may send some patch to that end.

>> 
>> .../devicetree/bindings/dma/apple,admac.yaml  | 68 +++++++++++++++++++
>> 1 file changed, 68 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..bbd5eaf5f709
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/dma/apple,admac.yaml
>> @@ -0,0 +1,68 @@
>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/dma/apple,admac.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: Apple Audio DMA Controller (ADMAC)
>> +
>> +description: |
>> +  Apple's Audio DMA Controller (ADMAC) is used to fetch and store audio samples
>> +  on SoCs from the "Apple Silicon" family.
>> +
>> +  The controller has been seen with up to 24 channels. Even-numbered channels
>> +  are TX-only, odd-numbered are RX-only. Individual channels are coupled to
>> +  fixed device endpoints.
>> +
>> +maintainers:
>> +  - Martin Povišer <povik+lin@...ebit.org>
>> +
>> +allOf:
>> +  - $ref: "dma-controller.yaml#"
>> +
>> +properties:
>> +  compatible:
>> +    items:
>> +      - enum:
>> +          - apple,t6000-admac
>> +          - apple,t8103-admac
>> +      - const: apple,admac
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  '#dma-cells':
>> +    const: 1
>> +    description:
>> +      Clients specify single cell with channel number.
>> +
>> +  dma-channels:
>> +    maximum: 24
>> +
>> +  interrupts:
>> +    minItems: 1
>> +    maxItems: 4
> 
> I'm now confused why this is variable. Put -1 entries on the end if 
> that's why it is variable.

That’s why. Fixed length it is then.

> 
> This needs some description about there being 1 of 4 outputs being 
> connected.

OK. Description there will be.

>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - '#dma-cells'
>> +  - dma-channels
>> +  - interrupts
>> +
>> +additionalProperties: false
>> +
>> +examples:
>> +  - |
>> +    #include <dt-bindings/interrupt-controller/apple-aic.h>
>> +    #include <dt-bindings/interrupt-controller/irq.h>
>> +
>> +    admac: dma-controller@...200000 {
>> +      compatible = "apple,t8103-admac", "apple,admac";
>> +      reg = <0x38200000 0x34000>;
>> +      dma-channels = <24>;
>> +      interrupt-parent = <&aic>;
>> +      interrupts = <AIC_IRQ 0xffffffff 0>,
>> +                   <AIC_IRQ 626 IRQ_TYPE_LEVEL_HIGH>;
>> +      #dma-cells = <1>;
>> +    };
>> -- 
>> 2.33.0
>> 
>> 

Martin