linux-kernel - Re: [PATCH 2/4] ASoC: meson: axg-fifo: add fifo depth to the bindings documentation

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Message-ID: <1jimmdbiyz.fsf@starbuckisacylon.baylibre.com>
Date:   Wed, 18 Dec 2019 19:13:08 +0100
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-amlogic@...ts.infradead.org,
        Kevin Hilman <khilman@...libre.com>
Subject: Re: [PATCH 2/4] ASoC: meson: axg-fifo: add fifo depth to the bindings documentation

On Wed 18 Dec 2019 at 18:50, Mark Brown <broonie@...nel.org> wrote:

> On Wed, Dec 18, 2019 at 06:24:18PM +0100, Jerome Brunet wrote:
>
>> Add a new property with the depth of the fifo in bytes. This is useful
>> since some instance of the fifo, even on the same SoC, may have different
>> depth. The depth is useful is set some parameters of the fifo.
>
> Can't we figure this out from the compatible strings?  They look SoC
> specific (which is good).  That means we don't need to add new
> properties for each quirk that separates the variants.

I don't think it would be appropriate in this case:

If I take the example of TODDR fifos on the SM1 SoC;
All the TODDR fifo on this SoC are compatible with the same driver and use:

compatible = "amlogic,sm1-toddr", "amlogic,axg-toddr";

However instance A on this SoC has a 8192B fifo while instance B, C and D
have 256B fifo. Same goes for the other SoC and also FRDDR fifos.

To store this difference using compatible I would have to add 1 compatible
string for each "A" instance of each FRDDR and TODDR of each SoC. At the
moment this would be 6 more compatible string for something that is really a
parameter ... This also shows that fifo depth is something the HW
manufacturer can tweak easily for each instances.

It would not scale which is why I went for a property.