ALSA: pcm: simplify top-up mode init in snd_pcm_playback_silence()

Inline the remaining call of snd_pcm_playback_hw_avail(). This makes
the top-up branch more congruent with the thresholded one, and allows
simplifying the handling of the corner cases.
Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230505155244.2312199-6-oswald.buddenhagen@gmx.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -90,15 +90,32 @@ void snd_pcm_playback_silence(struct snd_pcm_substream *substream, snd_pcm_ufram
 		 * This filling mode aims at free-running mode (used for example by dmix),
 		 * which doesn't update the application pointer.
 		 */
-		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;
+		snd_pcm_uframes_t hw_ptr = runtime->status->hw_ptr;
+		if (new_hw_ptr == ULONG_MAX) {
+			/*
+			 * Initialization, fill the whole unused buffer with silence.
+			 *
+			 * Usually, this is entered while stopped, before data is queued,
+			 * so both pointers are expected to be zero.
+			 */
+			snd_pcm_sframes_t avail = runtime->control->appl_ptr - hw_ptr;
+			if (avail < 0)
+				avail += runtime->boundary;
+			/*
+			 * In free-running mode, appl_ptr will be zero even while running,
+			 * so we end up with a huge number. There is no useful way to
+			 * handle this, so we just clear the whole buffer.
+			 */
+			runtime->silence_filled = avail > runtime->buffer_size ? 0 : avail;
+			runtime->silence_start = hw_ptr;
 		} else {
-			update_silence_vars(runtime, runtime->status->hw_ptr, new_hw_ptr);
+			/* Silence the just played area immediately */
+			update_silence_vars(runtime, hw_ptr, new_hw_ptr);
 		}
+		/*
+		 * In this mode, silence_filled actually includes the valid
+		 * sample data from the user.
+		 */
 		frames = runtime->buffer_size - runtime->silence_filled;
 	}
 	if (snd_BUG_ON(frames > runtime->buffer_size))