[ALSA] usb-audio: allow pausing

Add pause capabilities for both USB playback and capture streams.

Signed-off-by: Clemens Ladisch <[e-mail]>
Signed-off-by: Jaroslav Kysela <[e-mail]>

sound/usb/usbaudio.c

···
 	return 0;
 }
 
+/*
+ * Process after capture complete when paused.  Nothing to do.
+ */
+static int retire_paused_capture_urb(struct snd_usb_substream *subs,
+				     struct snd_pcm_runtime *runtime,
+				     struct urb *urb)
+{
+	return 0;
+}
+
 
 /*
  * prepare urb for full speed playback sync pipe
···
 }
 
 /*
- * Prepare urb for streaming before playback starts.
+ * Prepare urb for streaming before playback starts or when paused.
  *
- * We don't yet have data, so we send a frame of silence.
+ * We don't have any data, so we send a frame of silence.
  */
-static int prepare_startup_playback_urb(struct snd_usb_substream *subs,
-					struct snd_pcm_runtime *runtime,
-					struct urb *urb)
+static int prepare_nodata_playback_urb(struct snd_usb_substream *subs,
+				       struct snd_pcm_runtime *runtime,
+				       struct urb *urb)
 {
 	unsigned int i, offs, counts;
 	struct snd_urb_ctx *ctx = urb->context;
···
  */
 static struct snd_urb_ops audio_urb_ops[2] = {
 	{
-		.prepare =	prepare_startup_playback_urb,
+		.prepare =	prepare_nodata_playback_urb,
 		.retire =	retire_playback_urb,
 		.prepare_sync =	prepare_playback_sync_urb,
 		.retire_sync =	retire_playback_sync_urb,
···
 
 static struct snd_urb_ops audio_urb_ops_high_speed[2] = {
 	{
-		.prepare =	prepare_startup_playback_urb,
+		.prepare =	prepare_nodata_playback_urb,
 		.retire =	retire_playback_urb,
 		.prepare_sync =	prepare_playback_sync_urb_hs,
 		.retire_sync =	retire_playback_sync_urb_hs,
···
 
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
+	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
 		subs->ops.prepare = prepare_playback_urb;
 		return 0;
 	case SNDRV_PCM_TRIGGER_STOP:
 		return deactivate_urbs(subs, 0, 0);
+	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+		subs->ops.prepare = prepare_nodata_playback_urb;
+		return 0;
 	default:
 		return -EINVAL;
 	}
···
 
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
+		subs->ops.retire = retire_capture_urb;
 		return start_urbs(subs, substream->runtime);
 	case SNDRV_PCM_TRIGGER_STOP:
 		return deactivate_urbs(subs, 0, 0);
+	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
+		subs->ops.retire = retire_paused_capture_urb;
+		return 0;
+	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
+		subs->ops.retire = retire_capture_urb;
+		return 0;
 	default:
 		return -EINVAL;
 	}
···
 	/* for playback, submit the URBs now; otherwise, the first hwptr_done
 	 * updates for all URBs would happen at the same time when starting */
 	if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK) {
-		subs->ops.prepare = prepare_startup_playback_urb;
+		subs->ops.prepare = prepare_nodata_playback_urb;
 		return start_urbs(subs, runtime);
 	} else
 		return 0;
···
 				SNDRV_PCM_INFO_MMAP_VALID |
 				SNDRV_PCM_INFO_BATCH |
 				SNDRV_PCM_INFO_INTERLEAVED |
-				SNDRV_PCM_INFO_BLOCK_TRANSFER,
+				SNDRV_PCM_INFO_BLOCK_TRANSFER |
+				SNDRV_PCM_INFO_PAUSE,
 	.buffer_bytes_max =	1024 * 1024,
 	.period_bytes_min =	64,
 	.period_bytes_max =	512 * 1024,