Re: [PATCH] ASoC: tegra: Fix Master Volume Control

[Jon Hunter <jonathanh@nvidia.com>]

On 13/06/2023 10:57, Takashi Iwai wrote:
> On Tue, 13 Jun 2023 11:55:16 +0200,
> Takashi Iwai wrote:
>>
>> On Tue, 13 Jun 2023 11:34:53 +0200,
>> Jon Hunter wrote:
>>>
>>> Commit 3ed2b549b39f ("ALSA: pcm: fix wait_time calculations") corrected
>>> the PCM wait_time calculations and in doing so reduced the calculated
>>> wait_time. This exposed an issue with the Tegra Master Volume Control
>>> (MVC) device where the reduced wait_time caused the MVC to fail. For now
>>> fix this by setting the default wait_time for Tegra to be 500ms.
>>>
>>> Fixes: 3ed2b549b39f ("ALSA: pcm: fix wait_time calculations")
>>> Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
>>
>> Hm, it's still not clear why it fails.  The commit above changes the
>> timeout of wait_for_avail() to the full-buffer + 10% margin.  In
>> thoery, the loop should abort after the full buffer read, and that
>> must be enough.  If there were a large FIFO behind, it might be
>> overflow, but the fifo_size of Tegra driver seems 4, so it's
>> negligible.
>>
>> If extending the timeout "fixes" the problem, it might indicate that
>> the period update IRQ is triggered too late.  Could you measure the
>> timing of each snd_pcm_period_elapsed() and wait_for_avail() call?
> 
> OTOH, it's already at a pretty late stage for 6.4, and we need an
> urgent regression fix.  So it's better to paper over it now, while
> hunting further for the real culprit.


I have filed a bug report internally to investigate this, but yes for 
now was hoping to get something in place for v6.4 to avoid any regressions.

Thanks
Jon

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