linux-kernel - Re: Context expectations in ALSA

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Date:   Thu, 22 Oct 2020 15:20:49 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, Dom Cobley <dom@...pberrypi.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Subject: Re: Context expectations in ALSA

On Thu, 22 Oct 2020 14:57:41 +0200,
Maxime Ripard wrote:
> 
> On Thu, Oct 22, 2020 at 12:03:19PM +0200, Jaroslav Kysela wrote:
> > Dne 22. 10. 20 v 11:50 Maxime Ripard napsal(a):
> > 
> > > So, I'm not really sure what I'm supposed to do here. The drivers
> > > involved don't appear to be doing anything extraordinary, but the issues
> > > lockdep report are definitely valid too. What are the expectations in
> > > terms of context from ALSA when running the callbacks, and how can we
> > > fix it?
> > 
> > I think that you should set the non-atomic flag and wake up the workqueue or
> > so from interrupt handler in this case. Call snd_pcm_period_elapsed() from the
> > workqueue not the interrupt handler context.
> 
> Yeah, that was my first guess too. However, the DMA driver uses some
> kind of generic helpers using a tasklet, so getting rid of it would take
> some work and would very likely not be eligible for stable.

Who sets the nonatomic flag for vc4?  I couldn't find the relevant
code in the latest upstream.

Ideally dmaengine PCM helper should support the nonatomic mode, but
until then, the other side needs to drop the nonatomic flag, I
suppose.


thanks,

Takashi