From 932a81519572156a88dbc2349d183c603446f9c4 Mon Sep 17 00:00:00 2001
From: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
Date: Wed, 13 Feb 2019 00:57:51 -0200
Subject: [PATCH] ALSA: pcm: Comment why read blocks when PCM is not running

This avoids bringing back the problem introduced by
62ba568f7aef ("ALSA: pcm: Return 0 when size <
start_threshold in capture") and fixed in 00a399cad1a0
("ALSA: pcm: Revert capture stream behavior change in
blocking mode"), which prevented the user from starting
capture from another thread.

Signed-off-by: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/pcm_lib.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index bcb06bd3d81d1..345ab1ab2cac4 100644
--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -2176,6 +2176,10 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
 	if (runtime->status->state == SNDRV_PCM_STATE_RUNNING)
 		snd_pcm_update_hw_ptr(substream);
 
+	/*
+	 * If size < start_threshold, wait indefinitely. Another
+	 * thread may start capture
+	 */
 	if (!is_playback &&
 	    runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
 	    size >= runtime->start_threshold) {
-- 
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