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Reply-To: wens@kernel.org
From: Chen-Yu Tsai <wens@kernel.org>
Date: Thu, 25 Jan 2024 23:45:29 +0800
Message-ID: <CAGb2v650reNd9n-epiCYs6dkbvaG9xARbyP6Rn9eDAKc-sS6+Q@mail.gmail.com>
Subject: Re: [PATCH 4/7] dt-bindings: dma: allwinner,sun50i-a64-dma: Add
 compatible for H616
To: Andre Przywara <andre.przywara@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>, 
	Jernej Skrabec <jernej.skrabec@gmail.com>, Samuel Holland <samuel@sholland.org>, 
	Liam Girdwood <lgirdwood@gmail.com>, Mark Brown <broonie@kernel.org>, 
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>, Vinod Koul <vkoul@kernel.org>, 
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, 
	linux-sunxi@lists.linux.dev, linux-sound@vger.kernel.org, 
	dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org
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On Thu, Jan 25, 2024 at 11:09=E2=80=AFPM Andre Przywara <andre.przywara@arm=
com> wrote:
>
> On Thu, 25 Jan 2024 22:37:34 +0800
> Chen-Yu Tsai <wens@kernel.org> wrote:
>
> Hi,
>
> > On Tue, Jan 23, 2024 at 8:41=E2=80=AFAM Andre Przywara <andre.przywara@=
arm.com> wrote:
> > >
> > > On Tue, 23 Jan 2024 01:05:15 +0800
> > > Chen-Yu Tsai <wens@kernel.org> wrote:
> > >
> > > Hi,
> > >
> > > > From: Chen-Yu Tsai <wens@csie.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) layo=
ut.
> > >
> > > That does not seem to be entirely true: The H616 encodes the two lowe=
st
> > > 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 th=
e
> > > 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?
>
> Yes, that's what I got as well.
>
> > > The good thing it that this encoding is backwards compatible, so I
> > > think the fallback string still holds: Any driver just implementing t=
he
> > > 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-9f0f=
934490ea@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-a=
100-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 addr=
ess
> > could be way off on the A100 and H616.
>
> I don't know the exact boundaries of "compatible" here, but the H6 manual
> pretty clearly states "The descriptor address must be word-aligned."
> But since the A100 compatible is known and supported for a while, that
> doesn't really matter, practically speaking, I guess.

I'd say that makes the descriptor address register backward compatible,

> One could check how the H6 DMA controller reacts to those bits not being
> 0, not sure if I find the time, though.

but no idea about the parameter field in the descriptor. So for now I
think we should just be cautious. Since as you mentioned the A100 is alread=
y
supported and listed separately, lets just keep that for now.

ChenYu

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