[alsa-devel] [PATCH v4] ALSA: compress: fix drain calls blocking other compress functions

[Vinod Koul]

The drain and drain_notify callback were blocked by low level driver untill the
draining was complete. Due to this being invoked with big fat mutex held, others
ops like reading timestamp, calling pause, drop were blocked.

So to fix this we add a new snd_compr_drain_notify() API. This would be required
to be invoked by low level driver when drain or partial drain has been completed
by the DSP. Thus we make the drain and partial_drain callback as non blocking
and driver returns immediately after notifying DSP.
The waiting is done while relasing the lock so that other ops can go ahead.

Signed-off-by: Vinod Koul <vinod.koul at intel.com>
CC: stable at vger.kernel.org
---
v4:
 move pr_err -> pr_debug to avoid spamming kernel log
 make wait in drain interruptible
v3:
 call snd_compr_drain_notify from compress_stop()
 rename draining -> drain_wake
 add some comments on state transistion after drain
v2:
 fix the 80 line warn
 move the state change to compress_drain()


 include/sound/compress_driver.h |   13 +++++++++
 sound/core/compress_offload.c   |   55 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
index 9031a26..e723935 100644
--- a/include/sound/compress_driver.h
+++ b/include/sound/compress_driver.h
@@ -48,6 +48,8 @@ struct snd_compr_ops;
  *	the ring buffer
  * @total_bytes_transferred: cumulative bytes transferred by offload DSP
  * @sleep: poll sleep
+ * @wait: drain wait queue
+ * @drain_wake: condition for drain wake
  */
 struct snd_compr_runtime {
 	snd_pcm_state_t state;
@@ -59,6 +61,8 @@ struct snd_compr_runtime {
 	u64 total_bytes_available;
 	u64 total_bytes_transferred;
 	wait_queue_head_t sleep;
+	wait_queue_head_t wait;
+	unsigned int drain_wake;
 	void *private_data;
 };
 
@@ -171,4 +175,13 @@ static inline void snd_compr_fragment_elapsed(struct snd_compr_stream *stream)
 	wake_up(&stream->runtime->sleep);
 }
 
+static inline void snd_compr_drain_notify(struct snd_compr_stream *stream)
+{
+	if (snd_BUG_ON(!stream))
+		return;
+
+	stream->runtime->drain_wake = 1;
+	wake_up(&stream->runtime->wait);
+}
+
 #endif
diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
index bea523a..645cec5 100644
--- a/sound/core/compress_offload.c
+++ b/sound/core/compress_offload.c
@@ -123,6 +123,7 @@ static int snd_compr_open(struct inode *inode, struct file *f)
 	}
 	runtime->state = SNDRV_PCM_STATE_OPEN;
 	init_waitqueue_head(&runtime->sleep);
+	init_waitqueue_head(&runtime->wait);
 	data->stream.runtime = runtime;
 	f->private_data = (void *)data;
 	mutex_lock(&compr->lock);
@@ -682,12 +683,48 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
 	if (!retval) {
 		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
 		wake_up(&stream->runtime->sleep);
+		snd_compr_drain_notify(stream);
 		stream->runtime->total_bytes_available = 0;
 		stream->runtime->total_bytes_transferred = 0;
 	}
 	return retval;
 }
 
+static int snd_compress_wait_for_drain(struct snd_compr_stream *stream)
+{
+	int ret;
+
+	/*
+	 * We are called with lock held. So drop the lock while we wait for
+	 * drain complete notfication from the driver
+	 *
+	 * It is expected that driver will notify the drain completion and then
+	 * stream will be moved to SETUP state, even if draining resulted in an
+	 * error. We can trigger next track after this.
+	 */
+	stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
+	mutex_unlock(&stream->device->lock);
+
+	/* we wait for drain to complete here, drain can return when
+	 * interruption occurred, wait returned error or success.
+	 * For the first two cases we don't do anything different here and
+	 * return after waking up
+	 */
+
+	ret = wait_event_interruptible(stream->runtime->wait,
+			stream->runtime->drain_wake);
+	if (ret == -ERESTARTSYS)
+		pr_debug("wait aborted by a signal");
+	else if (ret)
+		pr_debug("wait for drain failed with %d\n", ret);
+
+
+	wake_up(&stream->runtime->sleep);
+	mutex_lock(&stream->device->lock);
+
+	return ret;
+}
+
 static int snd_compr_drain(struct snd_compr_stream *stream)
 {
 	int retval;
@@ -695,11 +732,17 @@ static int snd_compr_drain(struct snd_compr_stream *stream)
 	if (stream->runtime->state == SNDRV_PCM_STATE_PREPARED ||
 			stream->runtime->state == SNDRV_PCM_STATE_SETUP)
 		return -EPERM;
+
+	stream->runtime->drain_wake = 0;
 	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_DRAIN);
-	if (!retval) {
-		stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
+	if (retval) {
+		pr_debug("SND_COMPR_TRIGGER_DRAIN failed %d\n", retval);
 		wake_up(&stream->runtime->sleep);
+		return retval;
 	}
+
+	retval = snd_compress_wait_for_drain(stream);
+	stream->runtime->state = SNDRV_PCM_STATE_SETUP;
 	return retval;
 }
 
@@ -735,10 +778,16 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream)
 	if (stream->next_track == false)
 		return -EPERM;
 
+	stream->runtime->drain_wake = 0;
 	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_PARTIAL_DRAIN);
+	if (retval) {
+		pr_debug("Partial drain returned failure\n");
+		wake_up(&stream->runtime->sleep);
+		return retval;
+	}
 
 	stream->next_track = false;
-	return retval;
+	return snd_compress_wait_for_drain(stream);
 }
 
 static long snd_compr_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
-- 
1.7.0.4