linux-kernel - Re: [PATCH 2/8] ASoC: tegra: Fix AMX byte map

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Date:   Fri, 23 Jun 2023 11:15:00 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Sameer Pujar <spujar@...dia.com>
Cc:     robh+dt@...nel.org, krzk+dt@...nel.org, thierry.reding@...il.com,
        lgirdwood@...il.com, perex@...ex.cz, tiwai@...e.com,
        jonathanh@...dia.com, mkumard@...dia.com, sheetal@...dia.com,
        alsa-devel@...a-project.org, devicetree@...r.kernel.org,
        linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 2/8] ASoC: tegra: Fix AMX byte map

On Fri, Jun 23, 2023 at 11:09:32AM +0530, Sameer Pujar wrote:
> On 22-06-2023 17:37, Mark Brown wrote:
> > On Thu, Jun 22, 2023 at 05:04:10PM +0530, Sameer Pujar wrote:

> > > Byte mask for channel-1 of stream-1 is not getting enabled and this
> > > causes failures during AMX use cases. The enable bit is not set during
> > > put() callback of byte map mixer control.

> > > This happens because the byte map value 0 matches the initial state
> > > of byte map array and put() callback returns without doing anything.

> > > Fix the put() callback by actually looking at the byte mask array
> > > to identify if any change is needed and update the fields accordingly.

> > I'm not quite sure I follow the logic here - I'd have expected this to
> > mean that there's a bootstrapping issue and that we should be doing some
> > more initialisation during startup such that the existing code which
> > checks if there is a change will be doing the right thing?

> The issue can happen in subsequent cycles as well if once the user disables
> the byte map by putting 256. It happens because of following reason where
> 256 value is reset to 0 since the byte map array is tightly packed and it
> can't store 256 value.

...

> > > Also update get() callback to return 256 if the byte map is disabled.
> > This will be a user visible change.  It's not clear to me why it's
> > needed - it seems like it's a hack to push users to do an update in the
> > case where they want to use channel 1 stream 1?

> Though it looks like 256 value is forced, but actually the user sees
> whatever value is set before. The 256 value storage is linked to byte mask
> value.

> I must admit that this is not easily readable. If you suggest to simplify
> this, I can check if storage space increase for byte map value can make it
> more readable. Thanks for your feedback.

This could definitely use more clarification I think.  It's not obvious
that storing 256 won't actually hold (and that should trigger a
complaint from mixer-test if that's what happens).

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