diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
index bcb06bd3d81d..345ab1ab2cac 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) {