[alsa-devel] [PATCH v2] ALSA: core: Allow drivers to set R/W wait time.

[Takashi Iwai]

On Mon, 02 Jul 2018 18:10:44 +0200,
Takashi Iwai wrote:
> 
> On Mon, 02 Jul 2018 18:04:54 +0200,
> Liam Girdwood wrote:
> > 
> > Currently ALSA core blocks userspace for about 10 seconds for PCM R/W IO.
> > This needs to be configurable for modern hardware like DSPs where no
> > pointer update in milliseconds can indicate terminal DSP errors.
> > 
> > Add a substream variable to set the wait time in ms. This allows userspace
> > and drivers to recover more quickly from terminal DSP errors.
> > 
> > Signed-off-by: Liam Girdwood <liam.r.girdwood at linux.intel.com>
> > ---
> > 
> > Changes since V1 :-
> > 
> >  o Remove API method and alow drivers to set directly.
> >  o Validate time is driver supplied times.
> > 
> >  include/sound/pcm.h  |  1 +
> >  sound/core/pcm_lib.c | 10 ++++++++--
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> > index e054c583d3b3..edad4a506b93 100644
> > --- a/include/sound/pcm.h
> > +++ b/include/sound/pcm.h
> > @@ -462,6 +462,7 @@ struct snd_pcm_substream {
> >          /* -- timer section -- */
> >  	struct snd_timer *timer;		/* timer */
> >  	unsigned timer_running: 1;	/* time is running */
> > +	unsigned wait_time;	/* time in ms for R/W to wait for avail */
> >  	/* -- next substream -- */
> >  	struct snd_pcm_substream *next;
> >  	/* -- linked substreams -- */
> > diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> > index 44b5ae833082..6909b896a6a1 100644
> > --- a/sound/core/pcm_lib.c
> > +++ b/sound/core/pcm_lib.c
> > @@ -1832,12 +1832,18 @@ static int wait_for_avail(struct snd_pcm_substream *substream,
> >  	if (runtime->no_period_wakeup)
> >  		wait_time = MAX_SCHEDULE_TIMEOUT;
> >  	else {
> > -		wait_time = 10;
> > +		/* use wait time from substream if available */
> > +		if (substream->wait_time) {
> > +			wait_time = substream->wait_time;
> > +		} else {
> > +			wait_time = 10 * 1000; /* 10 secs */
> > +		}
> > +
> 
> This seems to be msec, but...
> 
> 
> >  		if (runtime->rate) {
> >  			long t = runtime->period_size * 2 / runtime->rate;
> >  			wait_time = max(t, wait_time);
> 
> ... here handled as a second.
> 
> >  		}
> > -		wait_time = msecs_to_jiffies(wait_time * 1000);
> > +		wait_time = msecs_to_jiffies(wait_time);
> 
> ... so this looks inconsistent.

And I think we can forget runtime->rate check if it's specified
explicitly.  That is, something like:

	/* use wait time from substream if available */
	if (substream->wait_time) {
		wait_time = substream->wait_time;
	} else {
		wait_time = 10; /* default 10 secs */
 		if (runtime->rate) {
 			long t = runtime->period_size * 2 / runtime->rate;
 			wait_time = max(t, wait_time);
 		}
		wait_time *= 1000;
	}
	wait_time = msecs_to_jiffies(wait_time * 1000);


Takashi