linux-kernel - Re: [PATCH 4/7] dt-bindings: dma: allwinner,sun50i-a64-dma: Add compatible for H616

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Date: Thu, 25 Jan 2024 22:37:34 +0800
From: Chen-Yu Tsai <wens@...nel.org>
To: Andre Przywara <andre.przywara@....com>
Cc: Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, Vinod Koul <vkoul@...nel.org>, 
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-sunxi@...ts.linux.dev, linux-sound@...r.kernel.org, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/7] dt-bindings: dma: allwinner,sun50i-a64-dma: Add
 compatible for H616

On Tue, Jan 23, 2024 at 8:41 AM Andre Przywara <andre.przywara@....com> wrote:
>
> On Tue, 23 Jan 2024 01:05:15 +0800
> Chen-Yu Tsai <wens@...nel.org> wrote:
>
> Hi,
>
> > From: Chen-Yu Tsai <wens@...e.org>
> >
> > The DMA controllers found on the H616 and H618 are the same as the one
> > found on the H6. The only difference is the DMA endpoint (DRQ) layout.
>
> That does not seem to be entirely true: The H616 encodes the two lowest
> bits in DMA_DESC_ADDR_REG differently: on the H6 they must be 0 (word
> aligned), on the H616 these contain bits [33:32] of the address of the
> DMA descriptor. The manual doesn't describe the descriptor format in
> much detail, but ec31c5c59492 suggests that those two bits are put in
> the "para" word of the descriptor.

Good catch. So, same as the A100 I believe?

> The good thing it that this encoding is backwards compatible, so I
> think the fallback string still holds: Any driver just implementing the
> H6 encoding would be able to drive the H616.
>
> I think the A100 was mis-described, as mentioned here:
> https://lore.kernel.org/linux-arm-kernel/29e575b6-14cb-73f1-512d-9f0f934490ea@arm.com/
> I think we should:
> - make the A100 use: "allwinner,sun50i-a100-dma", "sun50i-h6-dma"
> - make the H616 use: "allwinner,sun50i-h616-dma", "allwinner,sun50i-a100-dma", "sun50i-h6-dma"
>
> Does that make sense?

I wouldn't call that exactly backward compatible. Say the driver forgot to
clear the two bits. It would work fine on the H6, but the accessed address
could be way off on the A100 and H616.


ChenYu

> Cheers,
> Andre
>
> > Since the number of channels and endpoints are described with additional
> > generic properties, just add a new H616-specific compatible string and
> > fallback to the H6 one.
> >
> > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > ---
> >  .../bindings/dma/allwinner,sun50i-a64-dma.yaml    | 15 +++++++++++----
> >  1 file changed, 11 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/dma/allwinner,sun50i-a64-dma.yaml b/Documentation/devicetree/bindings/dma/allwinner,sun50i-a64-dma.yaml
> > index ec2d7a789ffe..e5693be378bd 100644
> > --- a/Documentation/devicetree/bindings/dma/allwinner,sun50i-a64-dma.yaml
> > +++ b/Documentation/devicetree/bindings/dma/allwinner,sun50i-a64-dma.yaml
> > @@ -28,6 +28,9 @@ properties:
> >        - items:
> >            - const: allwinner,sun8i-r40-dma
> >            - const: allwinner,sun50i-a64-dma
> > +      - items:
> > +          - const: allwinner,sun50i-h616-dma
> > +          - const: allwinner,sun50i-h6-dma
> >
> >    reg:
> >      maxItems: 1
> > @@ -59,10 +62,14 @@ required:
> >  if:
> >    properties:
> >      compatible:
> > -      enum:
> > -        - allwinner,sun20i-d1-dma
> > -        - allwinner,sun50i-a100-dma
> > -        - allwinner,sun50i-h6-dma
> > +      oneOf:
> > +        - enum:
> > +            - allwinner,sun20i-d1-dma
> > +            - allwinner,sun50i-a100-dma
> > +            - allwinner,sun50i-h6-dma
> > +        - items:
> > +            - const: allwinner,sun50i-h616-dma
> > +            - const: allwinner,sun50i-h6-dma
> >
> >  then:
> >    properties:
>