ALSA: pcm: add SNDRV_PCM_TRIGGER_DRAIN trigger

Add SNDRV_PCM_TRIGGER_DRAIN trigger for pcm drain.

Some audio devices require notification of drain events
in order to properly drain and shutdown an audio stream.

Signed-off-by: Libin Yang <libin.yang@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_native.c

@@ -420,7 +420,8 @@ int snd_pcm_hw_refine(struct snd_pcm_substream *substream,
 
 	hw = &substream->runtime->hw;
 	if (!params->info) {
-		params->info = hw->info & ~SNDRV_PCM_INFO_FIFO_IN_FRAMES;
+		params->info = hw->info & ~(SNDRV_PCM_INFO_FIFO_IN_FRAMES |
+					    SNDRV_PCM_INFO_DRAIN_TRIGGER);
 		if (!hw_support_mmap(substream))
 			params->info &= ~(SNDRV_PCM_INFO_MMAP |
 					  SNDRV_PCM_INFO_MMAP_VALID);
@@ -1566,6 +1567,13 @@ static int snd_pcm_do_drain_init(struct snd_pcm_substream *substream, int state)
 			snd_pcm_post_stop(substream, new_state);
 		}
 	}
+
+	if (runtime->status->state == SNDRV_PCM_STATE_DRAINING &&
+	    runtime->trigger_master == substream &&
+	    (runtime->hw.info & SNDRV_PCM_INFO_DRAIN_TRIGGER))
+		return substream->ops->trigger(substream,
+					       SNDRV_PCM_TRIGGER_DRAIN);
+
 	return 0;
 }