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

[Takashi Iwai]

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 at linux.intel.com>

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.



>  #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?

Also, how is user-space supposed to set the new parameter?


thanks,

Takashi