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

From: Sameer Pujar <spujar@nvidia.com>
To: Mark Brown <broonie@kernel.org>
Cc: robh+dt@kernel.org, krzk+dt@kernel.org, thierry.reding@gmail.com,
	lgirdwood@gmail.com, perex@perex.cz, tiwai@suse.com,
	jonathanh@nvidia.com, mkumard@nvidia.com, sheetal@nvidia.com,
	alsa-devel@alsa-project.org, devicetree@vger.kernel.org,
	linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH 2/8] ASoC: tegra: Fix AMX byte map
Date: Mon, 26 Jun 2023 15:11:45 +0530	[thread overview]
Message-ID: <020c7602-34c5-f31e-22aa-da0032854489@nvidia.com> (raw)
In-Reply-To: <ZJVwpE5KeL8rgvB9@finisterre.sirena.org.uk>

On 23-06-2023 15:45, Mark Brown wrote:
> 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).

OK. I will provide more clarifications in the commit message and the 
driver for the existing failure. Will put a TODO item in the driver to 
improve the logic and make it more readable.