RE: [PATCH] ALSA: compress: allow pause and resume during draining

["Gyeongtaek Lee" <gt82.lee@samsung.com>]

On 10/08/20 06:49 PM, Takashi Iwai wrote:
>On Mon, 12 Oct 2020 16:46:56 +0200,
>Jaroslav Kysela wrote:
>> 
>> Dne 12. 10. 20 v 16:21 Takashi Iwai napsal(a):
>> 
>> > But, I doubt whether we really need to care about that; as mentioned
>> > earlier, there is little to change from the user-space side.  It just
>> > pause or resume.  The only difference is the resume target, and
>> > honestly speaking, there is no interest in it from user-space side.
>> > And, the rest is about the kernel internal, and this can be really
>> > done in the way of the original patch.  The flow is quite simple and
>> > understandable...
>> 
>> The core compress code already uses the state mechanism (although internally).
>> 
>> Also, it's really unclear if all drivers were checked, if the pause triggers
>> can be called from the drain state (I know it's another point, but the drivers
>> should probably offer a flag that they support this). And why to call the
>> pause release callback when there's no pause (drain + release ioctl instead
>> drain + pause + release ioctl)? It's a clear midlevel code fault. This
>> protection should be there not in the hw drivers.
>> 
>> I refer the original patch:
>>   https://lore.kernel.org/alsa-devel/000c01d69585$228db6b0$67a92410$@samsung.com/
>
>Point taken, and yes, this should be handled conditionally only for
>the drivers that do support such a mode.
>
Thanks for all your advices.
I updated the patch from original as all your comments.

1. API 'snd_compr_use_pause_in_draining' is added to allow pause during draining
   only when the hw driver allow it explicitly.
2. Flag 'pause_in_draining' is added to the struct snd_compr_stream to check whether
   the stream has been paused during draining when snd_compr_resume is called.
   I need this change in the older stable kernels. 
   However, changing states is too complicated and even dangerous for not only kernel
   but also userspace as this discussion.
   So, I'd like to suggest to use this simple flag first, and then apply more patch
   which fixes this patch to use states for compress after SNDRV_COMPRESS_STATE_*
   is applied to the ALSA mainline by Vinod.

Following is the fixed patch. 
If there is more points should be fixed or discussed, just let me know.


With a stream with low bitrate, user can't pause or resume the stream
near the end of the stream because current ALSA doesn't allow it.
If the stream has very low bitrate enough to store whole stream into
the buffer, user can't do anything except stop the stream and then
restart it from the first.
If pause, resume are allowed during draining, user experience can be
enhanced.

Signed-off-by: Gyeongtaek Lee <gt82.lee@samsung.com>
Cc: stable@vger.kernel.org
---
 include/sound/compress_driver.h | 17 +++++++++++++
 sound/core/compress_offload.c   | 44 +++++++++++++++++++++++++++------
 2 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/include/sound/compress_driver.h b/include/sound/compress_driver.h
index 70cbc5095e72..5a0d6737de5e 100644
--- a/include/sound/compress_driver.h
+++ b/include/sound/compress_driver.h
@@ -67,6 +67,7 @@ struct snd_compr_runtime {
  * @metadata_set: metadata set flag, true when set
  * @next_track: has userspace signal next track transition, true when set
  * @partial_drain: undergoing partial_drain for stream, true when set
+ * @pause_in_draining: paused during draining state, true when set
  * @private_data: pointer to DSP private data
  * @dma_buffer: allocated buffer if any
  */
@@ -80,6 +81,7 @@ struct snd_compr_stream {
 	bool metadata_set;
 	bool next_track;
 	bool partial_drain;
+	bool pause_in_draining;
 	void *private_data;
 	struct snd_dma_buffer dma_buffer;
 };
@@ -142,6 +144,7 @@ struct snd_compr_ops {
  * @direction: Playback or capture direction
  * @lock: device lock
  * @device: device id
+ * @use_pause_in_draining: allow pause in draining, true when set
  */
 struct snd_compr {
 	const char *name;
@@ -152,6 +155,7 @@ struct snd_compr {
 	unsigned int direction;
 	struct mutex lock;
 	int device;
+	bool use_pause_in_draining;
 #ifdef CONFIG_SND_VERBOSE_PROCFS
 	/* private: */
 	char id[64];
@@ -166,6 +170,19 @@ int snd_compress_deregister(struct snd_compr *device);
 int snd_compress_new(struct snd_card *card, int device,
 			int type, const char *id, struct snd_compr *compr);
 
+/**
+ * snd_compr_use_pause_in_draining - Allow pause and resume in draining state
+ * @substream: compress substream to set
+ *
+ * Allow pause and resume in draining state.
+ * Only HW driver supports this transition can call this API.
+ */
+static inline void snd_compr_use_pause_in_draining(
+					struct snd_compr_stream *substream)
+{
+	substream->device->use_pause_in_draining = true;
+}
+
 /* dsp driver callback apis
  * For playback: driver should call snd_compress_fragment_elapsed() to let the
  * framework know that a fragment has been consumed from the ring buffer
diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
index 0e53f6f31916..a071485383ed 100644
--- a/sound/core/compress_offload.c
+++ b/sound/core/compress_offload.c
@@ -708,11 +708,24 @@ static int snd_compr_pause(struct snd_compr_stream *stream)
 {
 	int retval;
 
-	if (stream->runtime->state != SNDRV_PCM_STATE_RUNNING)
+	switch (stream->runtime->state) {
+	case SNDRV_PCM_STATE_RUNNING:
+		retval = stream->ops->trigger(stream,
+			SNDRV_PCM_TRIGGER_PAUSE_PUSH);
+		if (!retval)
+			stream->runtime->state = SNDRV_PCM_STATE_PAUSED;
+		break;
+	case SNDRV_PCM_STATE_DRAINING:
+		if (!stream->device->use_pause_in_draining)
+			return -EPERM;
+		retval = stream->ops->trigger(stream,
+			SNDRV_PCM_TRIGGER_PAUSE_PUSH);
+		if (!retval)
+			stream->pause_in_draining = true;
+		break;
+	default:
 		return -EPERM;
-	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_PUSH);
-	if (!retval)
-		stream->runtime->state = SNDRV_PCM_STATE_PAUSED;
+	}
 	return retval;
 }
 
@@ -720,11 +733,25 @@ static int snd_compr_resume(struct snd_compr_stream *stream)
 {
 	int retval;
 
-	if (stream->runtime->state != SNDRV_PCM_STATE_PAUSED)
+	switch (stream->runtime->state) {
+	case SNDRV_PCM_STATE_PAUSED:
+		retval = stream->ops->trigger(stream,
+			SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
+		if (!retval)
+			stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
+		break;
+	case SNDRV_PCM_STATE_DRAINING:
+		if (!stream->device->use_pause_in_draining ||
+		    !stream->pause_in_draining)
+			return -EPERM;
+		retval = stream->ops->trigger(stream,
+			SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
+		if (!retval)
+			stream->pause_in_draining = false;
+		break;
+	default:
 		return -EPERM;
-	retval = stream->ops->trigger(stream, SNDRV_PCM_TRIGGER_PAUSE_RELEASE);
-	if (!retval)
-		stream->runtime->state = SNDRV_PCM_STATE_RUNNING;
+	}
 	return retval;
 }
 
@@ -767,6 +794,7 @@ static int snd_compr_stop(struct snd_compr_stream *stream)
 		/* clear flags and stop any drain wait */
 		stream->partial_drain = false;
 		stream->metadata_set = false;
+		stream->pause_in_draining = false;
 		snd_compr_drain_notify(stream);
 		stream->runtime->total_bytes_available = 0;
 		stream->runtime->total_bytes_transferred = 0;

base-commit: 865c50e1d279671728c2936cb7680eb89355eeea
-- 
2.21.0
>
>Takashi
>