[alsa-devel] [PATCH] 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
---
v2:
 fix the 80 line warn
 move the state change to compress_drain()

 include/sound/compress_driver.h |   12 ++++++++++
 sound/core/compress_offload.c   |   43 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
index 9031a26..eff5f84 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 queuq
+ * @draining: draining wait condition
  */
 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 draining;
 	void *private_data;
 };
 
@@ -171,4 +175,12 @@ 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)
+{
+	snd_BUG_ON(!stream);
+
+	stream->runtime->draining = 1;
+	wake_up(&stream->runtime->wait);
+}
+
 #endif
diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
index bea523a..c030365 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 +683,36 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
 	if (!retval) {
 		stream->runtime->state = SNDRV_PCM_STATE_SETUP;
 		wake_up(&stream->runtime->sleep);
+		stream->runtime->draining = 1;
+		wake_up(&stream->runtime->wait);
 		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 retval = 0;
+
+	/*
+	 * we are called with lock held. So drop the lock while we wait for
+	 * drain complete notfication from the driver
+	 */
+	stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
+	mutex_unlock(&stream->device->lock);
+
+	retval = wait_event_interruptible(stream->runtime->wait,
+			stream->runtime->draining);
+	if (retval)
+		pr_err("Wait for drain failed %d\n", retval);
+
+	wake_up(&stream->runtime->sleep);
+	mutex_lock(&stream->device->lock);
+
+	return retval;
+}
+
 static int snd_compr_drain(struct snd_compr_stream *stream)
 {
 	int retval;
@@ -695,11 +720,17 @@ 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->draining = 0;
 	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_DRAIN);
-	if (!retval) {
-		stream->runtime->state = SNDRV_PCM_STATE_DRAINING;
+	if (retval) {
+		pr_err("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 +766,16 @@ static int snd_compr_partial_drain(struct snd_compr_stream *stream)
 	if (stream->next_track == false)
 		return -EPERM;
 
+	stream->runtime->draining = 0;
 	retval = stream->ops->trigger(stream, SND_COMPR_TRIGGER_PARTIAL_DRAIN);
+	if (retval) {
+		pr_err("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