On Wed, 2018-03-14 at 23:04 +0100, Takashi Iwai wrote:
> On Wed, 14 Mar 2018 21:44:40 +0100,
> 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@xxxxxxxxxxxxxxx>
>
> The idea looks good, though, a bit of nitpicking:
>
> > ---
> > include/sound/pcm.h | 6 ++++++
> > sound/core/pcm_lib.c | 15 ++++++++++-----
> > 2 files changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/sound/pcm.h b/include/sound/pcm.h
> > index e054c583d3b3..e4694684c524 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
> > */
>
> I'd name wait_timeout, which is slightly clearer.
>
>
> > /* -- next substream -- */
> > struct snd_pcm_substream *next;
> > /* -- linked substreams -- */
> > @@ -579,6 +580,11 @@ int snd_pcm_start(struct snd_pcm_substream *substream);
> > int snd_pcm_stop(struct snd_pcm_substream *substream, snd_pcm_state_t
> > status);
> > int snd_pcm_drain_done(struct snd_pcm_substream *substream);
> > int snd_pcm_stop_xrun(struct snd_pcm_substream *substream);
> > +static inline void snd_pcm_wait_time(struct snd_pcm_substream *substream,
> > + unsigned wait_time)
> > +{
> > + substream->wait_time = wait_time;
> > +}
>
> IMO, it's a simple one parameter, and no need wrapping with an inline
> function.
This was for drivers to set the parameter according to HW capabilities.
>
>
>
> > #ifdef CONFIG_PM
> > int snd_pcm_suspend(struct snd_pcm_substream *substream);
> > int snd_pcm_suspend_all(struct snd_pcm *pcm);
> > diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> > index a83152e7d387..2ee76c70f55f 100644
> > --- a/sound/core/pcm_lib.c
> > +++ b/sound/core/pcm_lib.c
> > @@ -1839,12 +1839,17 @@ static int wait_for_avail(struct snd_pcm_substream
> > *substream,
> > if (runtime->no_period_wakeup)
> > wait_time = MAX_SCHEDULE_TIMEOUT;
> > else {
> > - wait_time = 10;
> > - if (runtime->rate) {
> > - long t = runtime->period_size * 2 / runtime->rate;
> > - wait_time = max(t, wait_time);
> > + /* use wait time from substream if available */
> > + if (substream->wait_time) {
> > + wait_time = msecs_to_jiffies(substream->wait_time);
> > + } else {
> > + wait_time = 10;
> > + if (runtime->rate) {
> > + long t = runtime->period_size * 2 /
> > runtime->rate;
> > + wait_time = max(t, wait_time);
> > + }
> > + wait_time = msecs_to_jiffies(wait_time * 1000);
> > }
> > - wait_time = msecs_to_jiffies(wait_time * 1000);
>
> This can go bad when wait_time is shorter than the period time.
> Some validation is needed?
>
Yes, and we should also validate no irq mode somehow too, probably using buffer
time.
> Also, how is user-space supposed to set the new parameter?
>
It's not atm, as it was being set by the driver. Would probably mean an ABI
change to PCM ops or a new ioctl ? The latter wont break the ABI and the default
value would remain if the ioctl was not called.
Liam
>
> thanks,
>
> Takashi
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