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

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Date:   Thu, 14 Apr 2022 10:43:40 -0500
From:   Rob Herring <robh@...nel.org>
To:     Martin Povišer <povik+lin@...ebit.org>
Cc:     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 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).

> 
> 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.

> 
>  .../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.

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

> +
> +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
> 
>