linux-kernel - Re: [PATCH v1] ASoC: meson: axg-fifo: set option to use raw spinlock

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Message-ID: <1jle1auhu9.fsf@starbuckisacylon.baylibre.com>
Date: Tue, 06 Aug 2024 11:21:50 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Mark Brown <broonie@...nel.org>,  linux-rt-users@...r.kernel.org,
  Arseniy Krasnov <avkrasnov@...utedevices.com>,  Liam Girdwood
 <lgirdwood@...il.com>,  Jaroslav Kysela <perex@...ex.cz>,  Takashi Iwai
 <tiwai@...e.com>,  Neil Armstrong <neil.armstrong@...aro.org>,  Kevin
 Hilman <khilman@...libre.com>,  Martin Blumenstingl
 <martin.blumenstingl@...glemail.com>,  alsa-devel@...a-project.org,
  linux-sound@...r.kernel.org,  linux-arm-kernel@...ts.infradead.org,
  linux-amlogic@...ts.infradead.org,  linux-kernel@...r.kernel.org,
  kernel@...rdevices.ru,  oxffffaa@...il.com,  Thomas Gleixner
 <tglx@...utronix.de>
Subject: Re: [PATCH v1] ASoC: meson: axg-fifo: set option to use raw spinlock

On Tue 06 Aug 2024 at 08:50, Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> On 2024-08-05 18:07:28 [+0200], Jerome Brunet wrote:
>> Hi Sebastian,
> Hi Jerome,
>
>> Thanks a lot for taking the time to dig into the driver specifics.
>> The IRQ handler is actually not awfully critical in this case. The HW
>> will continue to run regardless of the IRQ being acked or not
>> 
>> The purpose of the handler is mainly to let Alsa know that 1 (or more)
>> period is ready. If alsa is too slow to react, and the buffer allows
>> just a few periods, the HW may under/overflow the buffer.
>> 
>> IRQF_ONESHOT is fine because snd_pcm_period_elapsed() 'notifies'
>> all past periods, not just one. The irq handler does not need to
>> run again until this function has been called. It also helps if the
>> period is ridiculously small, to try to reduce the number of IRQs.
>
> IRQF_ONESHOT is used to disable to keep the IRQ line disabled (after the
> primary handler) while the threaded handler is running. This implies
> that the primary handler must not be threaded under PREEMPT_RT.
> …

This is the point I was missing. It is clear now. Thanks a lot.

I have tweaked #1 and added a few tags but the gist remains the same.
I was going to add you under 'Suggested-by' but maybe putting you as the
actual Author would be more appropriate. 

What do you prefer ?