ALSA: pcm: rewrite snd_pcm_playback_silence()

The auto-silencer supports two modes: "thresholded" to fill up "just
enough", and "top-up" to fill up "as much as possible". The two modes
used rather distinct code paths, which this patch unifies. The only
remaining distinction is how much we actually want to fill.

This fixes a bug in thresholded mode, where we failed to use new_hw_ptr,
resulting in under-fill.

Top-up mode is now more well-behaved and much easier to understand in
corner cases.

This also updates comments in the proximity of silencing-related data
structures.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230420113324.877164-1-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 36 insertions, 50 deletions

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index af1eb136feb0..d21c73944efd 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -42,70 +42,56 @@ static int fill_silence_frames(struct snd_pcm_substream *substream,
  *
  * when runtime->silence_size >= runtime->boundary - fill processed area with silence immediately
  */
-void snd_pcm_playback_silence(struct snd_pcm_substream *substream, snd_pcm_uframes_t new_hw_ptr)
+void snd_pcm_playback_silence(struct snd_pcm_substream *substream)
 {
 	struct snd_pcm_runtime *runtime = substream->runtime;
-	snd_pcm_uframes_t frames, ofs, transfer;
+	snd_pcm_uframes_t appl_ptr = READ_ONCE(runtime->control->appl_ptr);
+	snd_pcm_sframes_t added, hw_avail, frames;
+	snd_pcm_uframes_t noise_dist, ofs, transfer;
 	int err;
 
+	added = appl_ptr - runtime->silence_start;
+	if (added) {
+		if (added < 0)
+			added += runtime->boundary;
+		if (added < runtime->silence_filled)
+			runtime->silence_filled -= added;
+		else
+			runtime->silence_filled = 0;
+		runtime->silence_start = appl_ptr;
+	}
+
+	// This will "legitimately" turn negative on underrun, and will be mangled
+	// into a huge number by the boundary crossing handling. The initial state
+	// might also be not quite sane. The code below MUST account for these cases.
+	hw_avail = appl_ptr - runtime->status->hw_ptr;
+	if (hw_avail < 0)
+		hw_avail += runtime->boundary;
+
+	noise_dist = hw_avail + runtime->silence_filled;
 	if (runtime->silence_size < runtime->boundary) {
-		snd_pcm_sframes_t noise_dist, n;
-		snd_pcm_uframes_t appl_ptr = READ_ONCE(runtime->control->appl_ptr);
-		if (runtime->silence_start != appl_ptr) {
-			n = appl_ptr - runtime->silence_start;
-			if (n < 0)
-				n += runtime->boundary;
-			if ((snd_pcm_uframes_t)n < runtime->silence_filled)
-				runtime->silence_filled -= n;
-			else
-				runtime->silence_filled = 0;
-			runtime->silence_start = appl_ptr;
-		}
-		if (runtime->silence_filled >= runtime->buffer_size)
-			return;
-		noise_dist = snd_pcm_playback_hw_avail(runtime) + runtime->silence_filled;
-		if (noise_dist >= (snd_pcm_sframes_t) runtime->silence_threshold)
-			return;
 		frames = runtime->silence_threshold - noise_dist;
+		if (frames <= 0)
+			return;
 		if (frames > runtime->silence_size)
 			frames = runtime->silence_size;
 	} else {
-		if (new_hw_ptr == ULONG_MAX) {	/* initialization */
-			snd_pcm_sframes_t avail = snd_pcm_playback_hw_avail(runtime);
-			if (avail > runtime->buffer_size)
-				avail = runtime->buffer_size;
-			runtime->silence_filled = avail > 0 ? avail : 0;
-			runtime->silence_start = (runtime->status->hw_ptr +
-						  runtime->silence_filled) %
-						 runtime->boundary;
-		} else {
-			ofs = runtime->status->hw_ptr;
-			frames = new_hw_ptr - ofs;
-			if ((snd_pcm_sframes_t)frames < 0)
-				frames += runtime->boundary;
-			runtime->silence_filled -= frames;
-			if ((snd_pcm_sframes_t)runtime->silence_filled < 0) {
-				runtime->silence_filled = 0;
-				runtime->silence_start = new_hw_ptr;
-			} else {
-				runtime->silence_start = ofs;
-			}
-		}
-		frames = runtime->buffer_size - runtime->silence_filled;
+		frames = runtime->buffer_size - noise_dist;
+		if (frames <= 0)
+			return;
 	}
+
 	if (snd_BUG_ON(frames > runtime->buffer_size))
 		return;
-	if (frames == 0)
-		return;
-	ofs = runtime->silence_start % runtime->buffer_size;
-	while (frames > 0) {
+	ofs = (runtime->silence_start + runtime->silence_filled) % runtime->buffer_size;
+	do {
 		transfer = ofs + frames > runtime->buffer_size ? runtime->buffer_size - ofs : frames;
 		err = fill_silence_frames(substream, ofs, transfer);
 		snd_BUG_ON(err < 0);
 		runtime->silence_filled += transfer;
 		frames -= transfer;
 		ofs = 0;
-	}
+	} while (frames > 0);
 	snd_pcm_dma_buffer_sync(substream, SNDRV_DMA_SYNC_DEVICE);
 }
 
@@ -439,10 +425,6 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
 		return 0;
 	}
 
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
-	    runtime->silence_size > 0)
-		snd_pcm_playback_silence(substream, new_hw_ptr);
-
 	if (in_interrupt) {
 		delta = new_hw_ptr - runtime->hw_ptr_interrupt;
 		if (delta < 0)
@@ -460,6 +442,10 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
 		runtime->hw_ptr_wrap += runtime->boundary;
 	}
 
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK &&
+	    runtime->silence_size > 0)
+		snd_pcm_playback_silence(substream);
+
 	update_audio_tstamp(substream, &curr_tstamp, &audio_tstamp);
 
 	return snd_pcm_update_state(substream, runtime);