Merge branch 'for-linus' into for-next

5 files changed, 23 insertions, 2 deletions

diff --git a/sound/usb/card.c b/sound/usb/card.c
index cf8f3953f78f..fd570a42f043 100644
--- a/sound/usb/card.c
+++ b/sound/usb/card.c
@@ -68,6 +68,7 @@ static int pid[SNDRV_CARDS] = { [0 ... (SNDRV_CARDS-1)] = -1 };
 static int device_setup[SNDRV_CARDS]; /* device parameter for this card */
 static bool ignore_ctl_error;
 static bool autoclock = true;
+static bool lowlatency = true;
 static char *quirk_alias[SNDRV_CARDS];
 static char *delayed_register[SNDRV_CARDS];
 static bool implicit_fb[SNDRV_CARDS];
@@ -93,6 +94,8 @@ MODULE_PARM_DESC(ignore_ctl_error,
 		 "Ignore errors from USB controller for mixer interfaces.");
 module_param(autoclock, bool, 0444);
 MODULE_PARM_DESC(autoclock, "Enable auto-clock selection for UAC2 devices (default: yes).");
+module_param(lowlatency, bool, 0444);
+MODULE_PARM_DESC(lowlatency, "Enable low latency playback (default: yes).");
 module_param_array(quirk_alias, charp, NULL, 0444);
 MODULE_PARM_DESC(quirk_alias, "Quirk aliases, e.g. 0123abcd:5678beef.");
 module_param_array(delayed_register, charp, NULL, 0444);
@@ -623,6 +626,7 @@ static int snd_usb_audio_create(struct usb_interface *intf,
 	chip->setup = device_setup[idx];
 	chip->generic_implicit_fb = implicit_fb[idx];
 	chip->autoclock = autoclock;
+	chip->lowlatency = lowlatency;
 	atomic_set(&chip->active, 1); /* avoid autopm during probing */
 	atomic_set(&chip->usage_count, 0);
 	atomic_set(&chip->shutdown, 0);
diff --git a/sound/usb/card.h b/sound/usb/card.h
index 6c0a052a28f9..5b19901f305a 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -94,6 +94,7 @@ struct snd_usb_endpoint {
 	struct list_head ready_playback_urbs; /* playback URB FIFO for implicit fb */
 
 	unsigned int nurbs;		/* # urbs */
+	unsigned int nominal_queue_size; /* total buffer sizes in URBs */
 	unsigned long active_mask;	/* bitmask of active urbs */
 	unsigned long unlink_mask;	/* bitmask of unlinked urbs */
 	char *syncbuf;			/* sync buffer for all sync URBs */
@@ -187,6 +188,7 @@ struct snd_usb_substream {
 	} dsd_dop;
 
 	bool trigger_tstamp_pending_update; /* trigger timestamp being updated from initial estimate */
+	bool early_playback_start;	/* early start needed for playback? */
 	struct media_ctl *media_ctl;
 };
 
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 79a8c569c62b..533919a28856 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1132,6 +1132,10 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep)
 		INIT_LIST_HEAD(&u->ready_list);
 	}
 
+	/* total buffer bytes of all URBs plus the next queue;
+	 * referred in pcm.c
+	 */
+	ep->nominal_queue_size = maxsize * urb_packs * (ep->nurbs + 1);
 	return 0;
 
 out_of_memory:
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 4e5031a68064..5dc9266180e3 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -614,6 +614,15 @@ static int snd_usb_pcm_prepare(struct snd_pcm_substream *substream)
 	subs->period_elapsed_pending = 0;
 	runtime->delay = 0;
 
+	/* check whether early start is needed for playback stream */
+	subs->early_playback_start =
+		subs->direction == SNDRV_PCM_STREAM_PLAYBACK &&
+		(!chip->lowlatency ||
+		 (subs->data_endpoint->nominal_queue_size >= subs->buffer_bytes));
+
+	if (subs->early_playback_start)
+		ret = start_endpoints(subs);
+
  unlock:
 	snd_usb_unlock_shutdown(chip);
 	return ret;
@@ -1394,7 +1403,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 		subs->trigger_tstamp_pending_update = false;
 	}
 
-	if (period_elapsed && !subs->running) {
+	if (period_elapsed && !subs->running && !subs->early_playback_start) {
 		subs->period_elapsed_pending = 1;
 		period_elapsed = 0;
 	}
@@ -1448,7 +1457,8 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
 					      prepare_playback_urb,
 					      retire_playback_urb,
 					      subs);
-		if (cmd == SNDRV_PCM_TRIGGER_START) {
+		if (!subs->early_playback_start &&
+		    cmd == SNDRV_PCM_TRIGGER_START) {
 			err = start_endpoints(subs);
 			if (err < 0) {
 				snd_usb_endpoint_set_callback(subs->data_endpoint,
diff --git a/sound/usb/usbaudio.h b/sound/usb/usbaudio.h
index 94261d19cceb..167834133b9b 100644
--- a/sound/usb/usbaudio.h
+++ b/sound/usb/usbaudio.h
@@ -55,6 +55,7 @@ struct snd_usb_audio {
 	bool generic_implicit_fb;	/* from the 'implicit_fb' module param */
 	bool autoclock;			/* from the 'autoclock' module param */
 
+	bool lowlatency;		/* from the 'lowlatency' module param */
 	struct usb_host_interface *ctrl_intf;	/* the audio control interface */
 	struct media_device *media_dev;
 	struct media_intf_devnode *ctl_intf_media_devnode;