[alsa-devel] [PATCH v4] ALSA: core: Allow drivers to set R/W wait time.

[Liam Girdwood]

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.

V2 :-
  o Max wait calc now in ms.
  o checkpatch. 

v3:-
  o Remove driver supplied time validation.

 include/sound/pcm.h  |  1 +
 sound/core/pcm_lib.c | 17 ++++++++++++-----
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
index e054c583d3b3..fcdf358a25f0 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 */
+	long 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..eecbfdc7a2c9 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1832,12 +1832,19 @@ 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 = 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);
 	}
 
 	for (;;) {
-- 
2.17.1