[PATCH v27 02/17] ALSA: pcm: report partial progress under the stream lock

[Joonho Lee <mynameisjune111@gmail.com>]

Allow a driver to publish subperiod progress under the PCM stream lock
without generating a period timer notification. Use the ordinary pointer
update, XRUN and wakeup path. Capture DRAINING can publish its final
tail while playback and other inactive states retain their existing
behavior.

Handle capture DRAINING separately in the state update: a full buffer is
still readable capture data, while progress beyond the buffer capacity
is an overrun. Playback continues to finish draining when its buffer is
empty.

Refresh capture availability after the unlocked copy and application
pointer commit while DRAINING. A final tail can arrive during the copy;
subtracting only the copied frames from the earlier snapshot can
otherwise finish draining with unread samples left in the ring.

Assisted-by: LLM
Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>

---
include/sound/pcm.h  |    1 +
 sound/core/pcm_lib.c |   40 +++++++++++++++++++++++++++++++++++++---
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/include/sound/pcm.h b/include/sound/pcm.h
--- a/include/sound/pcm.h
+++ b/include/sound/pcm.h
@@ -1182,6 +1182,7 @@
 int snd_pcm_lib_ioctl(struct snd_pcm_substream *substream,
 		      unsigned int cmd, void *arg);                      
 void snd_pcm_period_elapsed_under_stream_lock(struct snd_pcm_substream *substream);
+void snd_pcm_progress_under_stream_lock(struct snd_pcm_substream *substream);
 void snd_pcm_period_elapsed(struct snd_pcm_substream *substream);
 snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
 				     void *buf, bool interleaved,
diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -215,8 +215,14 @@
 	if (avail > runtime->avail_max)
 		runtime->avail_max = avail;
 	if (runtime->state == SNDRV_PCM_STATE_DRAINING) {
-		if (avail >= runtime->buffer_size) {
-			snd_pcm_drain_done(substream);
+		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+			if (avail >= runtime->buffer_size) {
+				snd_pcm_drain_done(substream);
+				return -EPIPE;
+			}
+		} else if (avail > runtime->buffer_size) {
+			/* A full capture buffer remains readable while draining. */
+			__snd_pcm_xrun(substream);
 			return -EPIPE;
 		}
 	} else {
@@ -1919,6 +1925,30 @@
 EXPORT_SYMBOL(snd_pcm_period_elapsed_under_stream_lock);
 
 /**
+ * snd_pcm_progress_under_stream_lock - Report progress without a period IRQ
+ * @substream: PCM substream
+ *
+ * Context: PCM stream lock held, with no driver pointer or trigger locks held.
+ * Updates the pointer and wakes readers for partial-period transfers. Capture
+ * streams may report their final tail while DRAINING. Unlike a period
+ * notification, this does not imply an elapsed period or tick the PCM timer.
+ * The same pointer, trigger and timestamp callbacks may be invoked.
+ */
+void snd_pcm_progress_under_stream_lock(struct snd_pcm_substream *substream)
+{
+	if (PCM_RUNTIME_CHECK(substream))
+		return;
+	if (!snd_pcm_running(substream) &&
+	    !(substream->stream == SNDRV_PCM_STREAM_CAPTURE &&
+	      substream->runtime->state == SNDRV_PCM_STATE_DRAINING))
+		return;
+	snd_pcm_update_hw_ptr(substream);
+	snd_kill_fasync(substream->runtime->fasync, SIGIO, POLL_IN);
+}
+EXPORT_SYMBOL_GPL(snd_pcm_progress_under_stream_lock);
+
+
+/**
  * snd_pcm_period_elapsed() - update the status of runtime for the next period by acquiring lock of
  *			      PCM substream.
  * @substream: the instance of PCM substream.
@@ -2405,7 +2435,11 @@
 		offset += frames;
 		size -= frames;
 		xfer += frames;
-		avail -= frames;
+		if (!is_playback &&
+		    runtime->state == SNDRV_PCM_STATE_DRAINING)
+			avail = snd_pcm_avail(substream);
+		else
+			avail -= frames;
 		if (is_playback &&
 		    runtime->state == SNDRV_PCM_STATE_PREPARED &&
 		    snd_pcm_playback_hw_avail(runtime) >= (snd_pcm_sframes_t)runtime->start_threshold) {