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Date:   Thu, 31 Aug 2023 13:24:44 +0100
From:   Mark Brown <broonie@kernel.org>
To:     John Watts <contact@jookia.org>
Cc:     alsa-devel@alsa-project.org, Liam Girdwood <lgirdwood@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        Jaroslav Kysela <perex@perex.cz>,
        Takashi Iwai <tiwai@suse.com>,
        Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= 
        <u.kleine-koenig@pengutronix.de>,
        Maxime Ripard <mripard@kernel.org>, devicetree@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 0/7] sun4i-i2s: Support channel remapping
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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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