[alsa-devel] [PATCH] 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>
---
 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 */
 	/* -- 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;
+}
 #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);
 	}
 
 	for (;;) {
-- 
2.14.1