Merge branch 'for-next' into for-linus

Merge 5.16-devel branch for upstreaming

Signed-off-by: Takashi Iwai <tiwai@suse.de>

17 files changed, 470 insertions, 139 deletions

diff --git a/sound/usb/6fire/comm.c b/sound/usb/6fire/comm.c
index 43a2a62d66f7..49629d4bb327 100644
--- a/sound/usb/6fire/comm.c
+++ b/sound/usb/6fire/comm.c
@@ -95,7 +95,7 @@ static int usb6fire_comm_send_buffer(u8 *buffer, struct usb_device *dev)
 	int actual_len;
 
 	ret = usb_interrupt_msg(dev, usb_sndintpipe(dev, COMM_EP),
-			buffer, buffer[1] + 2, &actual_len, HZ);
+			buffer, buffer[1] + 2, &actual_len, 1000);
 	if (ret < 0)
 		return ret;
 	else if (actual_len != buffer[1] + 2)
diff --git a/sound/usb/6fire/firmware.c b/sound/usb/6fire/firmware.c
index 8981e61f2da4..c51abc54d2f8 100644
--- a/sound/usb/6fire/firmware.c
+++ b/sound/usb/6fire/firmware.c
@@ -160,7 +160,7 @@ static int usb6fire_fw_ezusb_write(struct usb_device *device,
 {
 	return usb_control_msg_send(device, 0, type,
 				    USB_DIR_OUT | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
-				    value, 0, data, len, HZ, GFP_KERNEL);
+				    value, 0, data, len, 1000, GFP_KERNEL);
 }
 
 static int usb6fire_fw_ezusb_read(struct usb_device *device,
@@ -168,7 +168,7 @@ static int usb6fire_fw_ezusb_read(struct usb_device *device,
 {
 	return usb_control_msg_recv(device, 0, type,
 				    USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
-				    value, 0, data, len, HZ, GFP_KERNEL);
+				    value, 0, data, len, 1000, GFP_KERNEL);
 }
 
 static int usb6fire_fw_fpga_write(struct usb_device *device,
@@ -178,7 +178,7 @@ static int usb6fire_fw_fpga_write(struct usb_device *device,
 	int ret;
 
 	ret = usb_bulk_msg(device, usb_sndbulkpipe(device, FPGA_EP), data, len,
-			&actual_len, HZ);
+			&actual_len, 1000);
 	if (ret < 0)
 		return ret;
 	else if (actual_len != len)
diff --git a/sound/usb/card.h b/sound/usb/card.h
index 5b19901f305a..87f042d06ce0 100644
--- a/sound/usb/card.h
+++ b/sound/usb/card.h
@@ -74,8 +74,9 @@ struct snd_usb_endpoint {
 
 	atomic_t state;		/* running state */
 
-	void (*prepare_data_urb) (struct snd_usb_substream *subs,
-				  struct urb *urb);
+	int (*prepare_data_urb) (struct snd_usb_substream *subs,
+				 struct urb *urb,
+				 bool in_stream_lock);
 	void (*retire_data_urb) (struct snd_usb_substream *subs,
 				 struct urb *urb);
 
@@ -94,9 +95,9 @@ 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 */
+	atomic_t submitted_urbs;	/* currently submitted urbs */
 	char *syncbuf;			/* sync buffer for all sync URBs */
 	dma_addr_t sync_dma;		/* DMA address of syncbuf */
 
@@ -125,6 +126,7 @@ struct snd_usb_endpoint {
 	int skip_packets;		/* quirks for devices to ignore the first n packets
 					   in a stream */
 	bool implicit_fb_sync;		/* syncs with implicit feedback */
+	bool lowlatency_playback;	/* low-latency playback mode */
 	bool need_setup;		/* (re-)need for configure? */
 
 	/* for hw constraints */
@@ -136,6 +138,7 @@ struct snd_usb_endpoint {
 	unsigned int cur_period_frames;
 	unsigned int cur_period_bytes;
 	unsigned int cur_buffer_periods;
+	unsigned char cur_clock;
 
 	spinlock_t lock;
 	struct list_head list;
@@ -188,7 +191,7 @@ 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? */
+	bool lowlatency_playback;	/* low-latency playback mode */
 	struct media_ctl *media_ctl;
 };
 
diff --git a/sound/usb/clock.c b/sound/usb/clock.c
index 81d5ce07d548..4dfe76416794 100644
--- a/sound/usb/clock.c
+++ b/sound/usb/clock.c
@@ -271,7 +271,7 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip,
 		return -EINVAL;
 	}
 
-	/* first, see if the ID we're looking for is a clock source already */
+	/* first, see if the ID we're looking at is a clock source already */
 	source = snd_usb_find_clock_source(chip, entity_id, proto);
 	if (source) {
 		entity_id = GET_VAL(source, proto, bClockID);
@@ -297,7 +297,7 @@ static int __uac_clock_find_source(struct snd_usb_audio *chip,
 			goto find_source;
 		}
 
-		/* the entity ID we are looking for is a selector.
+		/* the entity ID we are looking at is a selector.
 		 * find out what it currently selects */
 		ret = uac_clock_selector_get_val(chip, clock_id);
 		if (ret < 0) {
@@ -496,6 +496,10 @@ int snd_usb_set_sample_rate_v2v3(struct snd_usb_audio *chip,
 	union uac23_clock_source_desc *cs_desc;
 
 	cs_desc = snd_usb_find_clock_source(chip, clock, fmt->protocol);
+
+	if (!cs_desc)
+		return 0;
+
 	if (fmt->protocol == UAC_VERSION_3)
 		bmControls = le32_to_cpu(cs_desc->v3.bmControls);
 	else
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 533919a28856..743b8287cfcd 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -148,18 +148,23 @@ int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep)
  * This won't be used for implicit feedback which takes the packet size
  * returned from the sync source
  */
-static int slave_next_packet_size(struct snd_usb_endpoint *ep)
+static int slave_next_packet_size(struct snd_usb_endpoint *ep,
+				  unsigned int avail)
 {
 	unsigned long flags;
+	unsigned int phase;
 	int ret;
 
 	if (ep->fill_max)
 		return ep->maxframesize;
 
 	spin_lock_irqsave(&ep->lock, flags);
-	ep->phase = (ep->phase & 0xffff)
-		+ (ep->freqm << ep->datainterval);
-	ret = min(ep->phase >> 16, ep->maxframesize);
+	phase = (ep->phase & 0xffff) + (ep->freqm << ep->datainterval);
+	ret = min(phase >> 16, ep->maxframesize);
+	if (avail && ret >= avail)
+		ret = -EAGAIN;
+	else
+		ep->phase = phase;
 	spin_unlock_irqrestore(&ep->lock, flags);
 
 	return ret;
@@ -169,20 +174,25 @@ static int slave_next_packet_size(struct snd_usb_endpoint *ep)
  * Return the number of samples to be sent in the next packet
  * for adaptive and synchronous endpoints
  */
-static int next_packet_size(struct snd_usb_endpoint *ep)
+static int next_packet_size(struct snd_usb_endpoint *ep, unsigned int avail)
 {
+	unsigned int sample_accum;
 	int ret;
 
 	if (ep->fill_max)
 		return ep->maxframesize;
 
-	ep->sample_accum += ep->sample_rem;
-	if (ep->sample_accum >= ep->pps) {
-		ep->sample_accum -= ep->pps;
+	sample_accum = ep->sample_accum + ep->sample_rem;
+	if (sample_accum >= ep->pps) {
+		sample_accum -= ep->pps;
 		ret = ep->packsize[1];
 	} else {
 		ret = ep->packsize[0];
 	}
+	if (avail && ret >= avail)
+		ret = -EAGAIN;
+	else
+		ep->sample_accum = sample_accum;
 
 	return ret;
 }
@@ -190,16 +200,27 @@ static int next_packet_size(struct snd_usb_endpoint *ep)
 /*
  * snd_usb_endpoint_next_packet_size: Return the number of samples to be sent
  * in the next packet
+ *
+ * If the size is equal or exceeds @avail, don't proceed but return -EAGAIN
+ * Exception: @avail = 0 for skipping the check.
  */
 int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep,
-				      struct snd_urb_ctx *ctx, int idx)
+				      struct snd_urb_ctx *ctx, int idx,
+				      unsigned int avail)
 {
-	if (ctx->packet_size[idx])
-		return ctx->packet_size[idx];
-	else if (ep->sync_source)
-		return slave_next_packet_size(ep);
+	unsigned int packet;
+
+	packet = ctx->packet_size[idx];
+	if (packet) {
+		if (avail && packet >= avail)
+			return -EAGAIN;
+		return packet;
+	}
+
+	if (ep->sync_source)
+		return slave_next_packet_size(ep, avail);
 	else
-		return next_packet_size(ep);
+		return next_packet_size(ep, avail);
 }
 
 static void call_retire_callback(struct snd_usb_endpoint *ep,
@@ -263,7 +284,7 @@ static void prepare_silent_urb(struct snd_usb_endpoint *ep,
 		unsigned int length;
 		int counts;
 
-		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i);
+		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, 0);
 		length = counts * ep->stride; /* number of silent bytes */
 		offset = offs * ep->stride + extra * i;
 		urb->iso_frame_desc[i].offset = offset;
@@ -286,8 +307,9 @@ static void prepare_silent_urb(struct snd_usb_endpoint *ep,
 /*
  * Prepare a PLAYBACK urb for submission to the bus.
  */
-static void prepare_outbound_urb(struct snd_usb_endpoint *ep,
-				 struct snd_urb_ctx *ctx)
+static int prepare_outbound_urb(struct snd_usb_endpoint *ep,
+				struct snd_urb_ctx *ctx,
+				bool in_stream_lock)
 {
 	struct urb *urb = ctx->urb;
 	unsigned char *cp = urb->transfer_buffer;
@@ -299,9 +321,9 @@ static void prepare_outbound_urb(struct snd_usb_endpoint *ep,
 	case SND_USB_ENDPOINT_TYPE_DATA:
 		data_subs = READ_ONCE(ep->data_subs);
 		if (data_subs && ep->prepare_data_urb)
-			ep->prepare_data_urb(data_subs, urb);
-		else /* no data provider, so send silence */
-			prepare_silent_urb(ep, ctx);
+			return ep->prepare_data_urb(data_subs, urb, in_stream_lock);
+		/* no data provider, so send silence */
+		prepare_silent_urb(ep, ctx);
 		break;
 
 	case SND_USB_ENDPOINT_TYPE_SYNC:
@@ -330,13 +352,14 @@ static void prepare_outbound_urb(struct snd_usb_endpoint *ep,
 
 		break;
 	}
+	return 0;
 }
 
 /*
  * Prepare a CAPTURE or SYNC urb for submission to the bus.
  */
-static inline void prepare_inbound_urb(struct snd_usb_endpoint *ep,
-				       struct snd_urb_ctx *urb_ctx)
+static int prepare_inbound_urb(struct snd_usb_endpoint *ep,
+			       struct snd_urb_ctx *urb_ctx)
 {
 	int i, offs;
 	struct urb *urb = urb_ctx->urb;
@@ -361,6 +384,7 @@ static inline void prepare_inbound_urb(struct snd_usb_endpoint *ep,
 		urb->iso_frame_desc[0].offset = 0;
 		break;
 	}
+	return 0;
 }
 
 /* notify an error as XRUN to the assigned PCM data substream */
@@ -396,6 +420,16 @@ next_packet_fifo_dequeue(struct snd_usb_endpoint *ep)
 	return p;
 }
 
+static void push_back_to_ready_list(struct snd_usb_endpoint *ep,
+				    struct snd_urb_ctx *ctx)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&ep->lock, flags);
+	list_add_tail(&ctx->ready_list, &ep->ready_playback_urbs);
+	spin_unlock_irqrestore(&ep->lock, flags);
+}
+
 /*
  * Send output urbs that have been prepared previously. URBs are dequeued
  * from ep->ready_playback_urbs and in case there aren't any available
@@ -406,12 +440,14 @@ next_packet_fifo_dequeue(struct snd_usb_endpoint *ep)
  * is that host controllers don't guarantee the order in which they return
  * inbound and outbound packets to their submitters.
  *
- * This function is only used for implicit feedback endpoints. For endpoints
- * driven by dedicated sync endpoints, URBs are immediately re-submitted
- * from their completion handler.
+ * This function is used both for implicit feedback endpoints and in low-
+ * latency playback mode.
  */
-static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
+void snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
+				       bool in_stream_lock)
 {
+	bool implicit_fb = snd_usb_endpoint_implicit_feedback_sink(ep);
+
 	while (ep_state_running(ep)) {
 
 		unsigned long flags;
@@ -420,14 +456,14 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
 		int err, i;
 
 		spin_lock_irqsave(&ep->lock, flags);
-		if (ep->next_packet_queued > 0 &&
+		if ((!implicit_fb || ep->next_packet_queued > 0) &&
 		    !list_empty(&ep->ready_playback_urbs)) {
 			/* take URB out of FIFO */
 			ctx = list_first_entry(&ep->ready_playback_urbs,
 					       struct snd_urb_ctx, ready_list);
 			list_del_init(&ctx->ready_list);
-
-			packet = next_packet_fifo_dequeue(ep);
+			if (implicit_fb)
+				packet = next_packet_fifo_dequeue(ep);
 		}
 		spin_unlock_irqrestore(&ep->lock, flags);
 
@@ -435,11 +471,24 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
 			return;
 
 		/* copy over the length information */
-		for (i = 0; i < packet->packets; i++)
-			ctx->packet_size[i] = packet->packet_size[i];
+		if (implicit_fb) {
+			for (i = 0; i < packet->packets; i++)
+				ctx->packet_size[i] = packet->packet_size[i];
+		}
 
 		/* call the data handler to fill in playback data */
-		prepare_outbound_urb(ep, ctx);
+		err = prepare_outbound_urb(ep, ctx, in_stream_lock);
+		/* can be stopped during prepare callback */
+		if (unlikely(!ep_state_running(ep)))
+			break;
+		if (err < 0) {
+			/* push back to ready list again for -EAGAIN */
+			if (err == -EAGAIN)
+				push_back_to_ready_list(ep, ctx);
+			else
+				notify_xrun(ep);
+			return;
+		}
 
 		err = usb_submit_urb(ctx->urb, GFP_ATOMIC);
 		if (err < 0) {
@@ -451,6 +500,7 @@ static void queue_pending_output_urbs(struct snd_usb_endpoint *ep)
 		}
 
 		set_bit(ctx->index, &ep->active_mask);
+		atomic_inc(&ep->submitted_urbs);
 	}
 }
 
@@ -461,7 +511,6 @@ static void snd_complete_urb(struct urb *urb)
 {
 	struct snd_urb_ctx *ctx = urb->context;
 	struct snd_usb_endpoint *ep = ctx->ep;
-	unsigned long flags;
 	int err;
 
 	if (unlikely(urb->status == -ENOENT ||		/* unlinked */
@@ -482,16 +531,20 @@ static void snd_complete_urb(struct urb *urb)
 		if (unlikely(!ep_state_running(ep)))
 			goto exit_clear;
 
-		if (snd_usb_endpoint_implicit_feedback_sink(ep)) {
-			spin_lock_irqsave(&ep->lock, flags);
-			list_add_tail(&ctx->ready_list, &ep->ready_playback_urbs);
+		/* in low-latency and implicit-feedback modes, push back the
+		 * URB to ready list at first, then process as much as possible
+		 */
+		if (ep->lowlatency_playback ||
+		     snd_usb_endpoint_implicit_feedback_sink(ep)) {
+			push_back_to_ready_list(ep, ctx);
 			clear_bit(ctx->index, &ep->active_mask);
-			spin_unlock_irqrestore(&ep->lock, flags);
-			queue_pending_output_urbs(ep);
+			snd_usb_queue_pending_output_urbs(ep, false);
+			atomic_dec(&ep->submitted_urbs); /* decrement at last */
 			return;
 		}
 
-		prepare_outbound_urb(ep, ctx);
+		/* in non-lowlatency mode, no error handling for prepare */
+		prepare_outbound_urb(ep, ctx, false);
 		/* can be stopped during prepare callback */
 		if (unlikely(!ep_state_running(ep)))
 			goto exit_clear;
@@ -513,6 +566,7 @@ static void snd_complete_urb(struct urb *urb)
 
 exit_clear:
 	clear_bit(ctx->index, &ep->active_mask);
+	atomic_dec(&ep->submitted_urbs);
 }
 
 /*
@@ -596,6 +650,7 @@ int snd_usb_add_endpoint(struct snd_usb_audio *chip, int ep_num, int type)
 	ep->type = type;
 	ep->ep_num = ep_num;
 	INIT_LIST_HEAD(&ep->ready_playback_urbs);
+	atomic_set(&ep->submitted_urbs, 0);
 
 	is_playback = ((ep_num & USB_ENDPOINT_DIR_MASK) == USB_DIR_OUT);
 	ep_num &= USB_ENDPOINT_NUMBER_MASK;
@@ -722,6 +777,7 @@ snd_usb_endpoint_open(struct snd_usb_audio *chip,
 		ep->cur_period_frames = params_period_size(params);
 		ep->cur_period_bytes = ep->cur_period_frames * ep->cur_frame_bytes;
 		ep->cur_buffer_periods = params_periods(params);
+		ep->cur_clock = fp->clock;
 
 		if (ep->type == SND_USB_ENDPOINT_TYPE_SYNC)
 			endpoint_set_syncinterval(chip, ep);
@@ -781,14 +837,19 @@ void snd_usb_endpoint_set_sync(struct snd_usb_audio *chip,
  * Pass NULL to deactivate each callback.
  */
 void snd_usb_endpoint_set_callback(struct snd_usb_endpoint *ep,
-				   void (*prepare)(struct snd_usb_substream *subs,
-						   struct urb *urb),
+				   int (*prepare)(struct snd_usb_substream *subs,
+						  struct urb *urb,
+						  bool in_stream_lock),
 				   void (*retire)(struct snd_usb_substream *subs,
 						  struct urb *urb),
 				   struct snd_usb_substream *data_subs)
 {
 	ep->prepare_data_urb = prepare;
 	ep->retire_data_urb = retire;
+	if (data_subs)
+		ep->lowlatency_playback = data_subs->lowlatency_playback;
+	else
+		ep->lowlatency_playback = false;
 	WRITE_ONCE(ep->data_subs, data_subs);
 }
 
@@ -833,6 +894,7 @@ void snd_usb_endpoint_close(struct snd_usb_audio *chip,
 		ep->altsetting = 0;
 		ep->cur_audiofmt = NULL;
 		ep->cur_rate = 0;
+		ep->cur_clock = 0;
 		ep->iface_ref = NULL;
 		usb_audio_dbg(chip, "EP 0x%x closed\n", ep->ep_num);
 	}
@@ -859,7 +921,7 @@ static int wait_clear_urbs(struct snd_usb_endpoint *ep)
 		return 0;
 
 	do {
-		alive = bitmap_weight(&ep->active_mask, ep->nurbs);
+		alive = atomic_read(&ep->submitted_urbs);
 		if (!alive)
 			break;
 
@@ -893,9 +955,10 @@ void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep)
  *
  * This function moves the EP to STOPPING state if it's being RUNNING.
  */
-static int stop_urbs(struct snd_usb_endpoint *ep, bool force)
+static int stop_urbs(struct snd_usb_endpoint *ep, bool force, bool keep_pending)
 {
 	unsigned int i;
+	unsigned long flags;
 
 	if (!force && atomic_read(&ep->running))
 		return -EBUSY;
@@ -903,9 +966,14 @@ static int stop_urbs(struct snd_usb_endpoint *ep, bool force)
 	if (!ep_state_update(ep, EP_STATE_RUNNING, EP_STATE_STOPPING))
 		return 0;
 
+	spin_lock_irqsave(&ep->lock, flags);
 	INIT_LIST_HEAD(&ep->ready_playback_urbs);
 	ep->next_packet_head = 0;
 	ep->next_packet_queued = 0;
+	spin_unlock_irqrestore(&ep->lock, flags);
+
+	if (keep_pending)
+		return 0;
 
 	for (i = 0; i < ep->nurbs; i++) {
 		if (test_bit(i, &ep->active_mask)) {
@@ -930,7 +998,7 @@ static int release_urbs(struct snd_usb_endpoint *ep, bool force)
 	snd_usb_endpoint_set_callback(ep, NULL, NULL, NULL);
 
 	/* stop and unlink urbs */
-	err = stop_urbs(ep, force);
+	err = stop_urbs(ep, force, false);
 	if (err)
 		return err;
 
@@ -1132,10 +1200,6 @@ 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:
@@ -1340,6 +1404,25 @@ unlock:
 	return err;
 }
 
+/* get the current rate set to the given clock by any endpoint */
+int snd_usb_endpoint_get_clock_rate(struct snd_usb_audio *chip, int clock)
+{
+	struct snd_usb_endpoint *ep;
+	int rate = 0;
+
+	if (!clock)
+		return 0;
+	mutex_lock(&chip->mutex);
+	list_for_each_entry(ep, &chip->ep_list, list) {
+		if (ep->cur_clock == clock && ep->cur_rate) {
+			rate = ep->cur_rate;
+			break;
+		}
+	}
+	mutex_unlock(&chip->mutex);
+	return rate;
+}
+
 /**
  * snd_usb_endpoint_start: start an snd_usb_endpoint
  *
@@ -1355,6 +1438,7 @@ unlock:
  */
 int snd_usb_endpoint_start(struct snd_usb_endpoint *ep)
 {
+	bool is_playback = usb_pipeout(ep->pipe);
 	int err;
 	unsigned int i;
 
@@ -1391,13 +1475,9 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep)
 
 	if (snd_usb_endpoint_implicit_feedback_sink(ep) &&
 	    !(ep->chip->quirk_flags & QUIRK_FLAG_PLAYBACK_FIRST)) {
-		for (i = 0; i < ep->nurbs; i++) {
-			struct snd_urb_ctx *ctx = ep->urb + i;
-			list_add_tail(&ctx->ready_list, &ep->ready_playback_urbs);
-		}
-
 		usb_audio_dbg(ep->chip, "No URB submission due to implicit fb sync\n");
-		return 0;
+		i = 0;
+		goto fill_rest;
 	}
 
 	for (i = 0; i < ep->nurbs; i++) {
@@ -1406,10 +1486,18 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep)
 		if (snd_BUG_ON(!urb))
 			goto __error;
 
-		if (usb_pipeout(ep->pipe)) {
-			prepare_outbound_urb(ep, urb->context);
-		} else {
-			prepare_inbound_urb(ep, urb->context);
+		if (is_playback)
+			err = prepare_outbound_urb(ep, urb->context, true);
+		else
+			err = prepare_inbound_urb(ep, urb->context);
+		if (err < 0) {
+			/* stop filling at applptr */
+			if (err == -EAGAIN)
+				break;
+			usb_audio_dbg(ep->chip,
+				      "EP 0x%x: failed to prepare urb: %d\n",
+				      ep->ep_num, err);
+			goto __error;
 		}
 
 		err = usb_submit_urb(urb, GFP_ATOMIC);
@@ -1420,14 +1508,29 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep)
 			goto __error;
 		}
 		set_bit(i, &ep->active_mask);
+		atomic_inc(&ep->submitted_urbs);
+	}
+
+	if (!i) {
+		usb_audio_dbg(ep->chip, "XRUN at starting EP 0x%x\n",
+			      ep->ep_num);
+		goto __error;
 	}
 
 	usb_audio_dbg(ep->chip, "%d URBs submitted for EP 0x%x\n",
-		      ep->nurbs, ep->ep_num);
+		      i, ep->ep_num);
+
+ fill_rest:
+	/* put the remaining URBs to ready list */
+	if (is_playback) {
+		for (; i < ep->nurbs; i++)
+			push_back_to_ready_list(ep, ep->urb + i);
+	}
+
 	return 0;
 
 __error:
-	snd_usb_endpoint_stop(ep);
+	snd_usb_endpoint_stop(ep, false);
 	return -EPIPE;
 }
 
@@ -1435,6 +1538,7 @@ __error:
  * snd_usb_endpoint_stop: stop an snd_usb_endpoint
  *
  * @ep: the endpoint to stop (may be NULL)
+ * @keep_pending: keep in-flight URBs
  *
  * A call to this function will decrement the running count of the endpoint.
  * In case the last user has requested the endpoint stop, the URBs will
@@ -1445,7 +1549,7 @@ __error:
  * The caller needs to synchronize the pending stop operation via
  * snd_usb_endpoint_sync_pending_stop().
  */
-void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
+void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending)
 {
 	if (!ep)
 		return;
@@ -1460,7 +1564,7 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
 	if (!atomic_dec_return(&ep->running)) {
 		if (ep->sync_source)
 			WRITE_ONCE(ep->sync_source->sync_sink, NULL);
-		stop_urbs(ep, false);
+		stop_urbs(ep, false, keep_pending);
 	}
 }
 
@@ -1575,7 +1679,7 @@ static void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
 		}
 
 		spin_unlock_irqrestore(&ep->lock, flags);
-		queue_pending_output_urbs(ep);
+		snd_usb_queue_pending_output_urbs(ep, false);
 
 		return;
 	}
diff --git a/sound/usb/endpoint.h b/sound/usb/endpoint.h
index a668f675b52b..6a9af04cf175 100644
--- a/sound/usb/endpoint.h
+++ b/sound/usb/endpoint.h
@@ -19,6 +19,7 @@ void snd_usb_endpoint_close(struct snd_usb_audio *chip,
 			    struct snd_usb_endpoint *ep);
 int snd_usb_endpoint_configure(struct snd_usb_audio *chip,
 			       struct snd_usb_endpoint *ep);
+int snd_usb_endpoint_get_clock_rate(struct snd_usb_audio *chip, int clock);
 
 bool snd_usb_endpoint_compatible(struct snd_usb_audio *chip,
 				 struct snd_usb_endpoint *ep,
@@ -29,14 +30,15 @@ void snd_usb_endpoint_set_sync(struct snd_usb_audio *chip,
 			       struct snd_usb_endpoint *data_ep,
 			       struct snd_usb_endpoint *sync_ep);
 void snd_usb_endpoint_set_callback(struct snd_usb_endpoint *ep,
-				   void (*prepare)(struct snd_usb_substream *subs,
-						   struct urb *urb),
+				   int (*prepare)(struct snd_usb_substream *subs,
+						  struct urb *urb,
+						  bool in_stream_lock),
 				   void (*retire)(struct snd_usb_substream *subs,
 						  struct urb *urb),
 				   struct snd_usb_substream *data_subs);
 
 int snd_usb_endpoint_start(struct snd_usb_endpoint *ep);
-void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep);
+void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep, bool keep_pending);
 void snd_usb_endpoint_sync_pending_stop(struct snd_usb_endpoint *ep);
 void snd_usb_endpoint_suspend(struct snd_usb_endpoint *ep);
 int  snd_usb_endpoint_activate(struct snd_usb_endpoint *ep);
@@ -45,6 +47,9 @@ void snd_usb_endpoint_free_all(struct snd_usb_audio *chip);
 
 int snd_usb_endpoint_implicit_feedback_sink(struct snd_usb_endpoint *ep);
 int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep,
-				      struct snd_urb_ctx *ctx, int idx);
+				      struct snd_urb_ctx *ctx, int idx,
+				      unsigned int avail);
+void snd_usb_queue_pending_output_urbs(struct snd_usb_endpoint *ep,
+				       bool in_stream_lock);
 
 #endif /* __USBAUDIO_ENDPOINT_H */
diff --git a/sound/usb/implicit.c b/sound/usb/implicit.c
index 23767a14d126..70319c822c10 100644
--- a/sound/usb/implicit.c
+++ b/sound/usb/implicit.c
@@ -54,8 +54,6 @@ static const struct snd_usb_implicit_fb_match playback_implicit_fb_quirks[] = {
 
 	/* Fixed EP */
 	/* FIXME: check the availability of generic matching */
-	IMPLICIT_FB_FIXED_DEV(0x1397, 0x0001, 0x81, 1), /* Behringer UFX1604 */
-	IMPLICIT_FB_FIXED_DEV(0x1397, 0x0002, 0x81, 1), /* Behringer UFX1204 */
 	IMPLICIT_FB_FIXED_DEV(0x2466, 0x8010, 0x81, 2), /* Fractal Audio Axe-Fx III */
 	IMPLICIT_FB_FIXED_DEV(0x31e9, 0x0001, 0x81, 2), /* Solid State Logic SSL2 */
 	IMPLICIT_FB_FIXED_DEV(0x31e9, 0x0002, 0x81, 2), /* Solid State Logic SSL2+ */
diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
index 9602929b7de9..59faa5a9a714 100644
--- a/sound/usb/line6/driver.c
+++ b/sound/usb/line6/driver.c
@@ -113,12 +113,12 @@ int line6_send_raw_message(struct usb_line6 *line6, const char *buffer,
 			retval = usb_interrupt_msg(line6->usbdev,
 						usb_sndintpipe(line6->usbdev, properties->ep_ctrl_w),
 						(char *)frag_buf, frag_size,
-						&partial, LINE6_TIMEOUT * HZ);
+						&partial, LINE6_TIMEOUT);
 		} else {
 			retval = usb_bulk_msg(line6->usbdev,
 						usb_sndbulkpipe(line6->usbdev, properties->ep_ctrl_w),
 						(char *)frag_buf, frag_size,
-						&partial, LINE6_TIMEOUT * HZ);
+						&partial, LINE6_TIMEOUT);
 		}
 
 		if (retval) {
@@ -347,7 +347,7 @@ int line6_read_data(struct usb_line6 *line6, unsigned address, void *data,
 	ret = usb_control_msg_send(usbdev, 0, 0x67,
 				   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
 				   (datalen << 8) | 0x21, address, NULL, 0,
-				   LINE6_TIMEOUT * HZ, GFP_KERNEL);
+				   LINE6_TIMEOUT, GFP_KERNEL);
 	if (ret) {
 		dev_err(line6->ifcdev, "read request failed (error %d)\n", ret);
 		goto exit;
@@ -360,7 +360,7 @@ int line6_read_data(struct usb_line6 *line6, unsigned address, void *data,
 		ret = usb_control_msg_recv(usbdev, 0, 0x67,
 					   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
 					   0x0012, 0x0000, &len, 1,
-					   LINE6_TIMEOUT * HZ, GFP_KERNEL);
+					   LINE6_TIMEOUT, GFP_KERNEL);
 		if (ret) {
 			dev_err(line6->ifcdev,
 				"receive length failed (error %d)\n", ret);
@@ -387,7 +387,7 @@ int line6_read_data(struct usb_line6 *line6, unsigned address, void *data,
 	/* receive the result: */
 	ret = usb_control_msg_recv(usbdev, 0, 0x67,
 				   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
-				   0x0013, 0x0000, data, datalen, LINE6_TIMEOUT * HZ,
+				   0x0013, 0x0000, data, datalen, LINE6_TIMEOUT,
 				   GFP_KERNEL);
 	if (ret)
 		dev_err(line6->ifcdev, "read failed (error %d)\n", ret);
@@ -417,7 +417,7 @@ int line6_write_data(struct usb_line6 *line6, unsigned address, void *data,
 
 	ret = usb_control_msg_send(usbdev, 0, 0x67,
 				   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
-				   0x0022, address, data, datalen, LINE6_TIMEOUT * HZ,
+				   0x0022, address, data, datalen, LINE6_TIMEOUT,
 				   GFP_KERNEL);
 	if (ret) {
 		dev_err(line6->ifcdev,
@@ -430,7 +430,7 @@ int line6_write_data(struct usb_line6 *line6, unsigned address, void *data,
 
 		ret = usb_control_msg_recv(usbdev, 0, 0x67,
 					   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
-					   0x0012, 0x0000, status, 1, LINE6_TIMEOUT * HZ,
+					   0x0012, 0x0000, status, 1, LINE6_TIMEOUT,
 					   GFP_KERNEL);
 		if (ret) {
 			dev_err(line6->ifcdev,
diff --git a/sound/usb/line6/driver.h b/sound/usb/line6/driver.h
index 71d3da1db8c8..ecf3a2b39c7e 100644
--- a/sound/usb/line6/driver.h
+++ b/sound/usb/line6/driver.h
@@ -27,7 +27,7 @@
 #define LINE6_FALLBACK_INTERVAL 10
 #define LINE6_FALLBACK_MAXPACKETSIZE 16
 
-#define LINE6_TIMEOUT 1
+#define LINE6_TIMEOUT 1000
 #define LINE6_BUFSIZE_LISTEN 64
 #define LINE6_MIDI_MESSAGE_MAXLEN 256
 
diff --git a/sound/usb/line6/podhd.c b/sound/usb/line6/podhd.c
index 28794a35949d..b24bc82f89e3 100644
--- a/sound/usb/line6/podhd.c
+++ b/sound/usb/line6/podhd.c
@@ -190,7 +190,7 @@ static int podhd_dev_start(struct usb_line6_podhd *pod)
 	ret = usb_control_msg_send(usbdev, 0,
 					0x67, USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
 					0x11, 0,
-					NULL, 0, LINE6_TIMEOUT * HZ, GFP_KERNEL);
+					NULL, 0, LINE6_TIMEOUT, GFP_KERNEL);
 	if (ret) {
 		dev_err(pod->line6.ifcdev, "read request failed (error %d)\n", ret);
 		goto exit;
@@ -200,7 +200,7 @@ static int podhd_dev_start(struct usb_line6_podhd *pod)
 	ret = usb_control_msg_recv(usbdev, 0, 0x67,
 					USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
 					0x11, 0x0,
-					init_bytes, 3, LINE6_TIMEOUT * HZ, GFP_KERNEL);
+					init_bytes, 3, LINE6_TIMEOUT, GFP_KERNEL);
 	if (ret) {
 		dev_err(pod->line6.ifcdev,
 			"receive length failed (error %d)\n", ret);
@@ -220,7 +220,7 @@ static int podhd_dev_start(struct usb_line6_podhd *pod)
 					USB_REQ_SET_FEATURE,
 					USB_TYPE_STANDARD | USB_RECIP_DEVICE | USB_DIR_OUT,
 					1, 0,
-					NULL, 0, LINE6_TIMEOUT * HZ, GFP_KERNEL);
+					NULL, 0, LINE6_TIMEOUT, GFP_KERNEL);
 exit:
 	return ret;
 }
diff --git a/sound/usb/line6/toneport.c b/sound/usb/line6/toneport.c
index 4e5693c97aa4..e33df58740a9 100644
--- a/sound/usb/line6/toneport.c
+++ b/sound/usb/line6/toneport.c
@@ -128,7 +128,7 @@ static int toneport_send_cmd(struct usb_device *usbdev, int cmd1, int cmd2)
 
 	ret = usb_control_msg_send(usbdev, 0, 0x67,
 				   USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
-				   cmd1, cmd2, NULL, 0, LINE6_TIMEOUT * HZ,
+				   cmd1, cmd2, NULL, 0, LINE6_TIMEOUT,
 				   GFP_KERNEL);
 
 	if (ret) {
diff --git a/sound/usb/misc/ua101.c b/sound/usb/misc/ua101.c
index 5834d1dc317e..4f6b20ed29dd 100644
--- a/sound/usb/misc/ua101.c
+++ b/sound/usb/misc/ua101.c
@@ -1000,7 +1000,7 @@ static int detect_usb_format(struct ua101 *ua)
 		fmt_playback->bSubframeSize * ua->playback.channels;
 
 	epd = &ua->intf[INTF_CAPTURE]->altsetting[1].endpoint[0].desc;
-	if (!usb_endpoint_is_isoc_in(epd)) {
+	if (!usb_endpoint_is_isoc_in(epd) || usb_endpoint_maxp(epd) == 0) {
 		dev_err(&ua->dev->dev, "invalid capture endpoint\n");
 		return -ENXIO;
 	}
@@ -1008,7 +1008,7 @@ static int detect_usb_format(struct ua101 *ua)
 	ua->capture.max_packet_bytes = usb_endpoint_maxp(epd);
 
 	epd = &ua->intf[INTF_PLAYBACK]->altsetting[1].endpoint[0].desc;
-	if (!usb_endpoint_is_isoc_out(epd)) {
+	if (!usb_endpoint_is_isoc_out(epd) || usb_endpoint_maxp(epd) == 0) {
 		dev_err(&ua->dev->dev, "invalid playback endpoint\n");
 		return -ENXIO;
 	}
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index 8e030b1c061a..6e7bac8203ba 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -361,9 +361,8 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 
 	memset(buf, 0, sizeof(buf));
 
-	ret = snd_usb_lock_shutdown(chip) ? -EIO : 0;
-	if (ret)
-		goto error;
+	if (snd_usb_lock_shutdown(chip))
+		return -EIO;
 
 	idx = mixer_ctrl_intf(cval->head.mixer) | (cval->head.id << 8);
 	ret = snd_usb_ctl_msg(chip->dev, usb_rcvctrlpipe(chip->dev, 0), bRequest,
@@ -372,8 +371,7 @@ static int get_ctl_value_v2(struct usb_mixer_elem_info *cval, int request,
 	snd_usb_unlock_shutdown(chip);
 
 	if (ret < 0) {
-error:
-		usb_audio_err(chip,
+		usb_audio_dbg(chip,
 			"cannot get ctl value: req = %#x, wValue = %#x, wIndex = %#x, type = %d\n",
 			request, validx, idx, cval->val_type);
 		return ret;
@@ -1208,12 +1206,32 @@ static void volume_control_quirks(struct usb_mixer_elem_info *cval,
 	}
 }
 
+/* forcibly initialize the current mixer value; if GET_CUR fails, set to
+ * the minimum as default
+ */
+static void init_cur_mix_raw(struct usb_mixer_elem_info *cval, int ch, int idx)
+{
+	int val, err;
+
+	err = snd_usb_get_cur_mix_value(cval, ch, idx, &val);
+	if (!err)
+		return;
+	if (!cval->head.mixer->ignore_ctl_error)
+		usb_audio_warn(cval->head.mixer->chip,
+			       "%d:%d: failed to get current value for ch %d (%d)\n",
+			       cval->head.id, mixer_ctrl_intf(cval->head.mixer),
+			       ch, err);
+	snd_usb_set_cur_mix_value(cval, ch, idx, cval->min);
+}
+
 /*
  * retrieve the minimum and maximum values for the specified control
  */
 static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
 				   int default_min, struct snd_kcontrol *kctl)
 {
+	int i, idx;
+
 	/* for failsafe */
 	cval->min = default_min;
 	cval->max = cval->min + 1;
@@ -1226,7 +1244,6 @@ static int get_min_max_with_quirks(struct usb_mixer_elem_info *cval,
 	} else {
 		int minchn = 0;
 		if (cval->cmask) {
-			int i;
 			for (i = 0; i < MAX_CHANNELS; i++)
 				if (cval->cmask & (1 << i)) {
 					minchn = i + 1;
@@ -1327,6 +1344,19 @@ no_res_check:
 		}
 	}
 
+	/* initialize all elements */
+	if (!cval->cmask) {
+		init_cur_mix_raw(cval, 0, 0);
+	} else {
+		idx = 0;
+		for (i = 0; i < MAX_CHANNELS; i++) {
+			if (cval->cmask & (1 << i)) {
+				init_cur_mix_raw(cval, i + 1, idx);
+				idx++;
+			}
+		}
+	}
+
 	return 0;
 }
 
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 46082dc57be0..d489c1de3bae 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -2795,6 +2795,7 @@ static int snd_bbfpro_controls_create(struct usb_mixer_interface *mixer)
 #define SND_DJM_750_IDX		0x1
 #define SND_DJM_850_IDX		0x2
 #define SND_DJM_900NXS2_IDX	0x3
+#define SND_DJM_750MK2_IDX	0x4
 
 
 #define SND_DJM_CTL(_name, suffix, _default_value, _windex) { \
@@ -2984,10 +2985,40 @@ static const struct snd_djm_ctl snd_djm_ctls_900nxs2[] = {
 	SND_DJM_CTL("Ch5 Input",   900nxs2_cap5, 3, SND_DJM_WINDEX_CAP)
 };
 
+// DJM-750MK2
+static const u16 snd_djm_opts_750mk2_cap1[] = {
+	0x0100, 0x0102, 0x0103, 0x0106, 0x0107, 0x0108, 0x0109, 0x010a };
+static const u16 snd_djm_opts_750mk2_cap2[] = {
+	0x0200, 0x0202, 0x0203, 0x0206, 0x0207, 0x0208, 0x0209, 0x020a };
+static const u16 snd_djm_opts_750mk2_cap3[] = {
+	0x0300, 0x0302, 0x0303, 0x0306, 0x0307, 0x0308, 0x0309, 0x030a };
+static const u16 snd_djm_opts_750mk2_cap4[] = {
+	0x0400, 0x0402, 0x0403, 0x0406, 0x0407, 0x0408, 0x0409, 0x040a };
+static const u16 snd_djm_opts_750mk2_cap5[] = {
+	0x0507, 0x0508, 0x0509, 0x050a, 0x0511, 0x0512, 0x0513, 0x0514 };
+
+static const u16 snd_djm_opts_750mk2_pb1[] = { 0x0100, 0x0101, 0x0104 };
+static const u16 snd_djm_opts_750mk2_pb2[] = { 0x0200, 0x0201, 0x0204 };
+static const u16 snd_djm_opts_750mk2_pb3[] = { 0x0300, 0x0301, 0x0304 };
+
+
+static const struct snd_djm_ctl snd_djm_ctls_750mk2[] = {
+	SND_DJM_CTL("Capture Level", cap_level, 0, SND_DJM_WINDEX_CAPLVL),
+	SND_DJM_CTL("Ch1 Input",   750mk2_cap1, 2, SND_DJM_WINDEX_CAP),
+	SND_DJM_CTL("Ch2 Input",   750mk2_cap2, 2, SND_DJM_WINDEX_CAP),
+	SND_DJM_CTL("Ch3 Input",   750mk2_cap3, 2, SND_DJM_WINDEX_CAP),
+	SND_DJM_CTL("Ch4 Input",   750mk2_cap4, 2, SND_DJM_WINDEX_CAP),
+	SND_DJM_CTL("Ch5 Input",   750mk2_cap5, 3, SND_DJM_WINDEX_CAP),
+	SND_DJM_CTL("Ch1 Output",   750mk2_pb1, 0, SND_DJM_WINDEX_PB),
+	SND_DJM_CTL("Ch2 Output",   750mk2_pb2, 1, SND_DJM_WINDEX_PB),
+	SND_DJM_CTL("Ch3 Output",   750mk2_pb3, 2, SND_DJM_WINDEX_PB)
+};
+
 
 static const struct snd_djm_device snd_djm_devices[] = {
 	SND_DJM_DEVICE(250mk2),
 	SND_DJM_DEVICE(750),
+	SND_DJM_DEVICE(750mk2),
 	SND_DJM_DEVICE(850),
 	SND_DJM_DEVICE(900nxs2)
 };
@@ -3235,6 +3266,9 @@ int snd_usb_mixer_apply_create_quirk(struct usb_mixer_interface *mixer)
 	case USB_ID(0x08e4, 0x017f): /* Pioneer DJ DJM-750 */
 		err = snd_djm_controls_create(mixer, SND_DJM_750_IDX);
 		break;
+	case USB_ID(0x2b73, 0x001b): /* Pioneer DJ DJM-750MK2 */
+		err = snd_djm_controls_create(mixer, SND_DJM_750MK2_IDX);
+		break;
 	case USB_ID(0x08e4, 0x0163): /* Pioneer DJ DJM-850 */
 		err = snd_djm_controls_create(mixer, SND_DJM_850_IDX);
 		break;
diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 5dc9266180e3..95ec8eec1bb0 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -219,16 +219,16 @@ int snd_usb_init_pitch(struct snd_usb_audio *chip,
 	return 0;
 }
 
-static bool stop_endpoints(struct snd_usb_substream *subs)
+static bool stop_endpoints(struct snd_usb_substream *subs, bool keep_pending)
 {
 	bool stopped = 0;
 
 	if (test_and_clear_bit(SUBSTREAM_FLAG_SYNC_EP_STARTED, &subs->flags)) {
-		snd_usb_endpoint_stop(subs->sync_endpoint);
+		snd_usb_endpoint_stop(subs->sync_endpoint, keep_pending);
 		stopped = true;
 	}
 	if (test_and_clear_bit(SUBSTREAM_FLAG_DATA_EP_STARTED, &subs->flags)) {
-		snd_usb_endpoint_stop(subs->data_endpoint);
+		snd_usb_endpoint_stop(subs->data_endpoint, keep_pending);
 		stopped = true;
 	}
 	return stopped;
@@ -261,7 +261,7 @@ static int start_endpoints(struct snd_usb_substream *subs)
 	return 0;
 
  error:
-	stop_endpoints(subs);
+	stop_endpoints(subs, false);
 	return err;
 }
 
@@ -437,7 +437,7 @@ static int configure_endpoints(struct snd_usb_audio *chip,
 
 	if (subs->data_endpoint->need_setup) {
 		/* stop any running stream beforehand */
-		if (stop_endpoints(subs))
+		if (stop_endpoints(subs, false))
 			sync_pending_stops(subs);
 		err = snd_usb_endpoint_configure(chip, subs->data_endpoint);
 		if (err < 0)
@@ -572,7 +572,7 @@ static int snd_usb_hw_free(struct snd_pcm_substream *substream)
 	subs->cur_audiofmt = NULL;
 	mutex_unlock(&chip->mutex);
 	if (!snd_usb_lock_shutdown(chip)) {
-		if (stop_endpoints(subs))
+		if (stop_endpoints(subs, false))
 			sync_pending_stops(subs);
 		close_endpoints(chip, subs);
 		snd_usb_unlock_shutdown(chip);
@@ -581,6 +581,26 @@ static int snd_usb_hw_free(struct snd_pcm_substream *substream)
 	return 0;
 }
 
+/* check whether early start is needed for playback stream */
+static int lowlatency_playback_available(struct snd_pcm_runtime *runtime,
+					 struct snd_usb_substream *subs)
+{
+	struct snd_usb_audio *chip = subs->stream->chip;
+
+	if (subs->direction == SNDRV_PCM_STREAM_CAPTURE)
+		return false;
+	/* disabled via module option? */
+	if (!chip->lowlatency)
+		return false;
+	/* free-wheeling mode? (e.g. dmix) */
+	if (runtime->stop_threshold > runtime->buffer_size)
+		return false;
+	/* implicit feedback mode has own operation mode */
+	if (snd_usb_endpoint_implicit_feedback_sink(subs->data_endpoint))
+		return false;
+	return true;
+}
+
 /*
  * prepare callback
  *
@@ -614,13 +634,8 @@ 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)
+	subs->lowlatency_playback = lowlatency_playback_available(runtime, subs);
+	if (!subs->lowlatency_playback)
 		ret = start_endpoints(subs);
 
  unlock:
@@ -734,6 +749,7 @@ static int hw_rule_rate(struct snd_pcm_hw_params *params,
 			struct snd_pcm_hw_rule *rule)
 {
 	struct snd_usb_substream *subs = rule->private;
+	struct snd_usb_audio *chip = subs->stream->chip;
 	const struct audioformat *fp;
 	struct snd_interval *it = hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
 	unsigned int rmin, rmax, r;
@@ -745,6 +761,14 @@ static int hw_rule_rate(struct snd_pcm_hw_params *params,
 	list_for_each_entry(fp, &subs->fmt_list, list) {
 		if (!hw_check_valid_format(subs, params, fp))
 			continue;
+		r = snd_usb_endpoint_get_clock_rate(chip, fp->clock);
+		if (r > 0) {
+			if (!snd_interval_test(it, r))
+				continue;
+			rmin = min(rmin, r);
+			rmax = max(rmax, r);
+			continue;
+		}
 		if (fp->rate_table && fp->nr_rates) {
 			for (i = 0; i < fp->nr_rates; i++) {
 				r = fp->rate_table[i];
@@ -1056,6 +1080,13 @@ static int setup_hw_info(struct snd_pcm_runtime *runtime, struct snd_usb_substre
 	if (err < 0)
 		return err;
 
+	list_for_each_entry(fp, &subs->fmt_list, list) {
+		if (fp->implicit_fb) {
+			runtime->hw.info |= SNDRV_PCM_INFO_JOINT_DUPLEX;
+			break;
+		}
+	}
+
 	return 0;
 }
 
@@ -1068,6 +1099,10 @@ static int snd_usb_pcm_open(struct snd_pcm_substream *substream)
 	int ret;
 
 	runtime->hw = snd_usb_hardware;
+	/* need an explicit sync to catch applptr update in low-latency mode */
+	if (direction == SNDRV_PCM_STREAM_PLAYBACK &&
+	    as->chip->lowlatency)
+		runtime->hw.info |= SNDRV_PCM_INFO_SYNC_APPLPTR;
 	runtime->private_data = subs;
 	subs->pcm_substream = substream;
 	/* runtime PM is also done there */
@@ -1320,44 +1355,66 @@ static unsigned int copy_to_urb_quirk(struct snd_usb_substream *subs,
 	return bytes;
 }
 
-static void prepare_playback_urb(struct snd_usb_substream *subs,
-				 struct urb *urb)
+static int prepare_playback_urb(struct snd_usb_substream *subs,
+				struct urb *urb,
+				bool in_stream_lock)
 {
 	struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
 	struct snd_usb_endpoint *ep = subs->data_endpoint;
 	struct snd_urb_ctx *ctx = urb->context;
-	unsigned int counts, frames, bytes;
+	unsigned int frames, bytes;
+	int counts;
+	unsigned int transfer_done, frame_limit, avail = 0;
 	int i, stride, period_elapsed = 0;
 	unsigned long flags;
+	int err = 0;
 
 	stride = ep->stride;
 
 	frames = 0;
 	ctx->queued = 0;
 	urb->number_of_packets = 0;
+
 	spin_lock_irqsave(&subs->lock, flags);
-	subs->frame_limit += ep->max_urb_frames;
+	frame_limit = subs->frame_limit + ep->max_urb_frames;
+	transfer_done = subs->transfer_done;
+
+	if (subs->lowlatency_playback &&
+	    runtime->status->state != SNDRV_PCM_STATE_DRAINING) {
+		unsigned int hwptr = subs->hwptr_done / stride;
+
+		/* calculate the byte offset-in-buffer of the appl_ptr */
+		avail = (runtime->control->appl_ptr - runtime->hw_ptr_base)
+			% runtime->buffer_size;
+		if (avail <= hwptr)
+			avail += runtime->buffer_size;
+		avail -= hwptr;
+	}
+
 	for (i = 0; i < ctx->packets; i++) {
-		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i);
+		counts = snd_usb_endpoint_next_packet_size(ep, ctx, i, avail);
+		if (counts < 0)
+			break;
 		/* set up descriptor */
 		urb->iso_frame_desc[i].offset = frames * stride;
 		urb->iso_frame_desc[i].length = counts * stride;
 		frames += counts;
+		avail -= counts;
 		urb->number_of_packets++;
-		subs->transfer_done += counts;
-		if (subs->transfer_done >= runtime->period_size) {
-			subs->transfer_done -= runtime->period_size;
-			subs->frame_limit = 0;
+		transfer_done += counts;
+		if (transfer_done >= runtime->period_size) {
+			transfer_done -= runtime->period_size;
+			frame_limit = 0;
 			period_elapsed = 1;
 			if (subs->fmt_type == UAC_FORMAT_TYPE_II) {
-				if (subs->transfer_done > 0) {
+				if (transfer_done > 0) {
 					/* FIXME: fill-max mode is not
 					 * supported yet */
-					frames -= subs->transfer_done;
-					counts -= subs->transfer_done;
+					frames -= transfer_done;
+					counts -= transfer_done;
 					urb->iso_frame_desc[i].length =
 						counts * stride;
-					subs->transfer_done = 0;
+					transfer_done = 0;
 				}
 				i++;
 				if (i < ctx->packets) {
@@ -1371,13 +1428,19 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 			}
 		}
 		/* finish at the period boundary or after enough frames */
-		if ((period_elapsed ||
-				subs->transfer_done >= subs->frame_limit) &&
+		if ((period_elapsed || transfer_done >= frame_limit) &&
 		    !snd_usb_endpoint_implicit_feedback_sink(ep))
 			break;
 	}
-	bytes = frames * stride;
 
+	if (!frames) {
+		err = -EAGAIN;
+		goto unlock;
+	}
+
+	bytes = frames * stride;
+	subs->transfer_done = transfer_done;
+	subs->frame_limit = frame_limit;
 	if (unlikely(ep->cur_format == SNDRV_PCM_FORMAT_DSD_U16_LE &&
 		     subs->cur_audiofmt->dsd_dop)) {
 		fill_playback_urb_dsd_dop(subs, urb, bytes);
@@ -1403,14 +1466,23 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
 		subs->trigger_tstamp_pending_update = false;
 	}
 
-	if (period_elapsed && !subs->running && !subs->early_playback_start) {
+	if (period_elapsed && !subs->running && subs->lowlatency_playback) {
 		subs->period_elapsed_pending = 1;
 		period_elapsed = 0;
 	}
+
+ unlock:
 	spin_unlock_irqrestore(&subs->lock, flags);
+	if (err < 0)
+		return err;
 	urb->transfer_buffer_length = bytes;
-	if (period_elapsed)
-		snd_pcm_period_elapsed(subs->pcm_substream);
+	if (period_elapsed) {
+		if (in_stream_lock)
+			snd_pcm_period_elapsed_under_stream_lock(subs->pcm_substream);
+		else
+			snd_pcm_period_elapsed(subs->pcm_substream);
+	}
+	return 0;
 }
 
 /*
@@ -1442,6 +1514,27 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
 		snd_pcm_period_elapsed(subs->pcm_substream);
 }
 
+/* PCM ack callback for the playback stream;
+ * this plays a role only when the stream is running in low-latency mode.
+ */
+static int snd_usb_pcm_playback_ack(struct snd_pcm_substream *substream)
+{
+	struct snd_usb_substream *subs = substream->runtime->private_data;
+	struct snd_usb_endpoint *ep;
+
+	if (!subs->lowlatency_playback || !subs->running)
+		return 0;
+	ep = subs->data_endpoint;
+	if (!ep)
+		return 0;
+	/* When no more in-flight URBs available, try to process the pending
+	 * outputs here
+	 */
+	if (!ep->active_mask)
+		snd_usb_queue_pending_output_urbs(ep, true);
+	return 0;
+}
+
 static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substream,
 					      int cmd)
 {
@@ -1457,7 +1550,7 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
 					      prepare_playback_urb,
 					      retire_playback_urb,
 					      subs);
-		if (!subs->early_playback_start &&
+		if (subs->lowlatency_playback &&
 		    cmd == SNDRV_PCM_TRIGGER_START) {
 			err = start_endpoints(subs);
 			if (err < 0) {
@@ -1473,7 +1566,7 @@ static int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substrea
 		return 0;
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_STOP:
-		stop_endpoints(subs);
+		stop_endpoints(subs, substream->runtime->status->state == SNDRV_PCM_STATE_DRAINING);
 		snd_usb_endpoint_set_callback(subs->data_endpoint,
 					      NULL, NULL, NULL);
 		subs->running = 0;
@@ -1521,7 +1614,7 @@ static int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream
 		return 0;
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_STOP:
-		stop_endpoints(subs);
+		stop_endpoints(subs, false);
 		fallthrough;
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
 		snd_usb_endpoint_set_callback(subs->data_endpoint,
@@ -1545,6 +1638,7 @@ static const struct snd_pcm_ops snd_usb_playback_ops = {
 	.trigger =	snd_usb_substream_playback_trigger,
 	.sync_stop =	snd_usb_pcm_sync_stop,
 	.pointer =	snd_usb_pcm_pointer,
+	.ack =		snd_usb_pcm_playback_ack,
 };
 
 static const struct snd_pcm_ops snd_usb_capture_ops = {
diff --git a/sound/usb/quirks-table.h b/sound/usb/quirks-table.h
index 2af8c68fac27..b1522e43173e 100644
--- a/sound/usb/quirks-table.h
+++ b/sound/usb/quirks-table.h
@@ -3894,6 +3894,64 @@ YAMAHA_DEVICE(0x7010, "UB99"),
 },
 {
 	/*
+	 * Pioneer DJ DJM-750MK2
+	 * 10 channels playback & 12 channels capture @ 48kHz S24LE
+	 */
+	USB_DEVICE_VENDOR_SPEC(0x2b73, 0x001b),
+	.driver_info = (unsigned long) &(const struct snd_usb_audio_quirk) {
+		.ifnum = QUIRK_ANY_INTERFACE,
+		.type = QUIRK_COMPOSITE,
+		.data = (const struct snd_usb_audio_quirk[]) {
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3LE,
+					.channels = 10,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.endpoint = 0x01,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC|
+					    USB_ENDPOINT_SYNC_ASYNC,
+					.rates = SNDRV_PCM_RATE_48000,
+					.rate_min = 48000,
+					.rate_max = 48000,
+					.nr_rates = 1,
+					.rate_table = (unsigned int[]) {
+						48000
+					}
+				}
+			},
+			{
+				.ifnum = 0,
+				.type = QUIRK_AUDIO_FIXED_ENDPOINT,
+				.data = &(const struct audioformat) {
+					.formats = SNDRV_PCM_FMTBIT_S24_3LE,
+					.channels = 12,
+					.iface = 0,
+					.altsetting = 1,
+					.altset_idx = 1,
+					.endpoint = 0x82,
+					.ep_idx = 1,
+					.ep_attr = USB_ENDPOINT_XFER_ISOC|
+						USB_ENDPOINT_SYNC_ASYNC|
+						USB_ENDPOINT_USAGE_IMPLICIT_FB,
+					.rates = SNDRV_PCM_RATE_48000,
+					.rate_min = 48000,
+					.rate_max = 48000,
+					.nr_rates = 1,
+					.rate_table = (unsigned int[]) { 48000 }
+				}
+			},
+			{
+				.ifnum = -1
+			}
+		}
+	}
+},
+{
+	/*
 	 * Pioneer DJ DJM-850
 	 * 8 channels playback and 8 channels capture @ 44.1/48/96kHz S24LE
 	 * Playback on EP 0x05
diff --git a/sound/usb/usx2y/usbusx2yaudio.c b/sound/usb/usx2y/usbusx2yaudio.c
index c39cc6851e2d..cfc1ea53978d 100644
--- a/sound/usb/usx2y/usbusx2yaudio.c
+++ b/sound/usb/usx2y/usbusx2yaudio.c
@@ -668,14 +668,15 @@ static void i_usx2y_04int(struct urb *urb)
 
 static int usx2y_rate_set(struct usx2ydev *usx2y, int rate)
 {
-	int			err = 0, i;
-	struct snd_usx2y_urb_seq	*us = NULL;
-	int			*usbdata = NULL;
-	const struct s_c2	*ra = rate == 48000 ? setrate_48000 : setrate_44100;
+	int err = 0, i;
+	struct snd_usx2y_urb_seq *us = NULL;
+	int *usbdata = NULL;
+	const struct s_c2 *ra = rate == 48000 ? setrate_48000 : setrate_44100;
 	struct urb *urb;
 
 	if (usx2y->rate != rate) {
-		us = kzalloc(sizeof(*us) + sizeof(struct urb *) * NOOF_SETRATE_URBS, GFP_KERNEL);
+		us = kzalloc(struct_size(us, urb, NOOF_SETRATE_URBS),
+			     GFP_KERNEL);
 		if (!us) {
 			err = -ENOMEM;
 			goto cleanup;