linux-kernel - Re: [RFC PATCH 0/7] sun4i-i2s: Support channel remapping

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Date:   Thu, 31 Aug 2023 13:24:44 +0100
From:   Mark Brown <broonie@...nel.org>
To:     John Watts <contact@...kia.org>
Cc:     alsa-devel@...a-project.org, Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Maxime Ripard <mripard@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/7] sun4i-i2s: Support channel remapping

On Sat, Aug 12, 2023 at 06:13:59AM +1000, John Watts wrote:

> First, I split up channel-dins and channel-slots. This is mainly
> because I implemented one first but both of them only make sense
> together. The registers themselves use a format of a byte per
> channel with the upper nibble being the din and the lower being
> the slot. Perhaps this is a better format to copy?

I think this is fine.

> Third, channel-slots is available on all sun4i-i2s controllers,
> but I only have it implemented on the R329 variant for now when
> there are multiple din pins.
> I could add support for this on older controllers but there's not
> really a use case for manual configuration as there's no DIN
> and I don't have hardware to test it on.

It's fine to leave this for someone who cares about that hardware to
implement, might be nice to add a warning if the properties are set but
not supported but it's not essential.

> Fourth, I don't limit the readable channels to the channels
> listed. Reading more channels than you have currently results in
> the controller assuming you want to use TDM, but that's not the
> case here and you can have strange duplicate channels show up.

It would be better to have constraints which prevent userspace doing the
wrong thing here.

> Fifth, it might be a good idea to increase the maximum channels
> from 8 to 16, especially if people are going to be running
> multiple TDM streams on one controller.

If there's no reason not to...

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