X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=sound%2Fusb%2Fendpoint.c;h=81c6edecd862356324f93c110aca9b88c9c2562c;hb=cd9a0b6bd67ec372b0ef3cb2abe26974f888b956;hp=7d46e482375d1dce4247f9805d81b6fc1c6568ba;hpb=41ebe9cde738a972d05c7282e09f5ed54cff0e8d;p=pandora-kernel.git

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 7d46e482375d..81c6edecd862 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -15,436 +15,951 @@
  *
  */
 
+#include <linux/gfp.h>
 #include <linux/init.h>
-#include <linux/slab.h>
 #include <linux/usb.h>
 #include <linux/usb/audio.h>
-#include <linux/usb/audio-v2.h>
 
 #include <sound/core.h>
 #include <sound/pcm.h>
 
 #include "usbaudio.h"
+#include "helper.h"
 #include "card.h"
-#include "proc.h"
-#include "quirks.h"
 #include "endpoint.h"
-#include "urb.h"
 #include "pcm.h"
-#include "helper.h"
-#include "format.h"
-#include "clock.h"
 
 /*
- * free a substream
+ * convert a sampling rate into our full speed format (fs/1000 in Q16.16)
+ * this will overflow at approx 524 kHz
  */
-static void free_substream(struct snd_usb_substream *subs)
+static inline unsigned get_usb_full_speed_rate(unsigned int rate)
 {
-	struct list_head *p, *n;
-
-	if (!subs->num_formats)
-		return; /* not initialized */
-	list_for_each_safe(p, n, &subs->fmt_list) {
-		struct audioformat *fp = list_entry(p, struct audioformat, list);
-		kfree(fp->rate_table);
-		kfree(fp);
-	}
-	kfree(subs->rate_list.list);
+	return ((rate << 13) + 62) / 125;
 }
 
+/*
+ * convert a sampling rate into USB high speed format (fs/8000 in Q16.16)
+ * this will overflow at approx 4 MHz
+ */
+static inline unsigned get_usb_high_speed_rate(unsigned int rate)
+{
+	return ((rate << 10) + 62) / 125;
+}
 
 /*
- * free a usb stream instance
+ * unlink active urbs.
  */
-static void snd_usb_audio_stream_free(struct snd_usb_stream *stream)
+static int deactivate_urbs(struct snd_usb_substream *subs, int force, int can_sleep)
 {
-	free_substream(&stream->substream[0]);
-	free_substream(&stream->substream[1]);
-	list_del(&stream->list);
-	kfree(stream);
+	struct snd_usb_audio *chip = subs->stream->chip;
+	unsigned int i;
+	int async;
+
+	subs->running = 0;
+
+	if (!force && subs->stream->chip->shutdown) /* to be sure... */
+		return -EBADFD;
+
+	async = !can_sleep && chip->async_unlink;
+
+	if (!async && in_interrupt())
+		return 0;
+
+	for (i = 0; i < subs->nurbs; i++) {
+		if (test_bit(i, &subs->active_mask)) {
+			if (!test_and_set_bit(i, &subs->unlink_mask)) {
+				struct urb *u = subs->dataurb[i].urb;
+				if (async)
+					usb_unlink_urb(u);
+				else
+					usb_kill_urb(u);
+			}
+		}
+	}
+	if (subs->syncpipe) {
+		for (i = 0; i < SYNC_URBS; i++) {
+			if (test_bit(i+16, &subs->active_mask)) {
+				if (!test_and_set_bit(i+16, &subs->unlink_mask)) {
+					struct urb *u = subs->syncurb[i].urb;
+					if (async)
+						usb_unlink_urb(u);
+					else
+						usb_kill_urb(u);
+				}
+			}
+		}
+	}
+	return 0;
 }
 
-static void snd_usb_audio_pcm_free(struct snd_pcm *pcm)
+
+/*
+ * release a urb data
+ */
+static void release_urb_ctx(struct snd_urb_ctx *u)
 {
-	struct snd_usb_stream *stream = pcm->private_data;
-	if (stream) {
-		stream->pcm = NULL;
-		snd_usb_audio_stream_free(stream);
+	if (u->urb) {
+		if (u->buffer_size)
+			usb_free_coherent(u->subs->dev, u->buffer_size,
+					u->urb->transfer_buffer,
+					u->urb->transfer_dma);
+		usb_free_urb(u->urb);
+		u->urb = NULL;
 	}
 }
 
+/*
+ *  wait until all urbs are processed.
+ */
+static int wait_clear_urbs(struct snd_usb_substream *subs)
+{
+	unsigned long end_time = jiffies + msecs_to_jiffies(1000);
+	unsigned int i;
+	int alive;
+
+	do {
+		alive = 0;
+		for (i = 0; i < subs->nurbs; i++) {
+			if (test_bit(i, &subs->active_mask))
+				alive++;
+		}
+		if (subs->syncpipe) {
+			for (i = 0; i < SYNC_URBS; i++) {
+				if (test_bit(i + 16, &subs->active_mask))
+					alive++;
+			}
+		}
+		if (! alive)
+			break;
+		schedule_timeout_uninterruptible(1);
+	} while (time_before(jiffies, end_time));
+	if (alive)
+		snd_printk(KERN_ERR "timeout: still %d active urbs..\n", alive);
+	return 0;
+}
 
 /*
- * add this endpoint to the chip instance.
- * if a stream with the same endpoint already exists, append to it.
- * if not, create a new pcm stream.
+ * release a substream
  */
-int snd_usb_add_audio_endpoint(struct snd_usb_audio *chip, int stream, struct audioformat *fp)
+void snd_usb_release_substream_urbs(struct snd_usb_substream *subs, int force)
 {
-	struct list_head *p;
-	struct snd_usb_stream *as;
-	struct snd_usb_substream *subs;
-	struct snd_pcm *pcm;
-	int err;
+	int i;
+
+	/* stop urbs (to be sure) */
+	deactivate_urbs(subs, force, 1);
+	wait_clear_urbs(subs);
+
+	for (i = 0; i < MAX_URBS; i++)
+		release_urb_ctx(&subs->dataurb[i]);
+	for (i = 0; i < SYNC_URBS; i++)
+		release_urb_ctx(&subs->syncurb[i]);
+	usb_free_coherent(subs->dev, SYNC_URBS * 4,
+			subs->syncbuf, subs->sync_dma);
+	subs->syncbuf = NULL;
+	subs->nurbs = 0;
+}
 
-	list_for_each(p, &chip->pcm_list) {
-		as = list_entry(p, struct snd_usb_stream, list);
-		if (as->fmt_type != fp->fmt_type)
-			continue;
-		subs = &as->substream[stream];
-		if (!subs->endpoint)
-			continue;
-		if (subs->endpoint == fp->endpoint) {
-			list_add_tail(&fp->list, &subs->fmt_list);
-			subs->num_formats++;
-			subs->formats |= fp->formats;
-			return 0;
+/*
+ * complete callback from data urb
+ */
+static void snd_complete_urb(struct urb *urb)
+{
+	struct snd_urb_ctx *ctx = urb->context;
+	struct snd_usb_substream *subs = ctx->subs;
+	struct snd_pcm_substream *substream = ctx->subs->pcm_substream;
+	int err = 0;
+
+	if ((subs->running && subs->ops.retire(subs, substream->runtime, urb)) ||
+	    !subs->running || /* can be stopped during retire callback */
+	    (err = subs->ops.prepare(subs, substream->runtime, urb)) < 0 ||
+	    (err = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
+		clear_bit(ctx->index, &subs->active_mask);
+		if (err < 0) {
+			snd_printd(KERN_ERR "cannot submit urb (err = %d)\n", err);
+			snd_pcm_stop(substream, SNDRV_PCM_STATE_XRUN);
 		}
 	}
-	/* look for an empty stream */
-	list_for_each(p, &chip->pcm_list) {
-		as = list_entry(p, struct snd_usb_stream, list);
-		if (as->fmt_type != fp->fmt_type)
-			continue;
-		subs = &as->substream[stream];
-		if (subs->endpoint)
-			continue;
-		err = snd_pcm_new_stream(as->pcm, stream, 1);
-		if (err < 0)
-			return err;
-		snd_usb_init_substream(as, stream, fp);
-		return 0;
+}
+
+
+/*
+ * complete callback from sync urb
+ */
+static void snd_complete_sync_urb(struct urb *urb)
+{
+	struct snd_urb_ctx *ctx = urb->context;
+	struct snd_usb_substream *subs = ctx->subs;
+	struct snd_pcm_substream *substream = ctx->subs->pcm_substream;
+	int err = 0;
+
+	if ((subs->running && subs->ops.retire_sync(subs, substream->runtime, urb)) ||
+	    !subs->running || /* can be stopped during retire callback */
+	    (err = subs->ops.prepare_sync(subs, substream->runtime, urb)) < 0 ||
+	    (err = usb_submit_urb(urb, GFP_ATOMIC)) < 0) {
+		clear_bit(ctx->index + 16, &subs->active_mask);
+		if (err < 0) {
+			snd_printd(KERN_ERR "cannot submit sync urb (err = %d)\n", err);
+			snd_pcm_stop(substream, SNDRV_PCM_STATE_XRUN);
+		}
 	}
+}
+
 
-	/* create a new pcm */
-	as = kzalloc(sizeof(*as), GFP_KERNEL);
-	if (!as)
-		return -ENOMEM;
-	as->pcm_index = chip->pcm_devs;
-	as->chip = chip;
-	as->fmt_type = fp->fmt_type;
-	err = snd_pcm_new(chip->card, "USB Audio", chip->pcm_devs,
-			  stream == SNDRV_PCM_STREAM_PLAYBACK ? 1 : 0,
-			  stream == SNDRV_PCM_STREAM_PLAYBACK ? 0 : 1,
-			  &pcm);
-	if (err < 0) {
-		kfree(as);
-		return err;
+/*
+ * initialize a substream for plaback/capture
+ */
+int snd_usb_init_substream_urbs(struct snd_usb_substream *subs,
+				unsigned int period_bytes,
+				unsigned int rate,
+				unsigned int frame_bits)
+{
+	unsigned int maxsize, i;
+	int is_playback = subs->direction == SNDRV_PCM_STREAM_PLAYBACK;
+	unsigned int urb_packs, total_packs, packs_per_ms;
+	struct snd_usb_audio *chip = subs->stream->chip;
+
+	/* calculate the frequency in 16.16 format */
+	if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
+		subs->freqn = get_usb_full_speed_rate(rate);
+	else
+		subs->freqn = get_usb_high_speed_rate(rate);
+	subs->freqm = subs->freqn;
+	subs->freqshift = INT_MIN;
+	/* calculate max. frequency */
+	if (subs->maxpacksize) {
+		/* whatever fits into a max. size packet */
+		maxsize = subs->maxpacksize;
+		subs->freqmax = (maxsize / (frame_bits >> 3))
+				<< (16 - subs->datainterval);
+	} else {
+		/* no max. packet size: just take 25% higher than nominal */
+		subs->freqmax = subs->freqn + (subs->freqn >> 2);
+		maxsize = ((subs->freqmax + 0xffff) * (frame_bits >> 3))
+				>> (16 - subs->datainterval);
 	}
-	as->pcm = pcm;
-	pcm->private_data = as;
-	pcm->private_free = snd_usb_audio_pcm_free;
-	pcm->info_flags = 0;
-	if (chip->pcm_devs > 0)
-		sprintf(pcm->name, "USB Audio #%d", chip->pcm_devs);
+	subs->phase = 0;
+
+	if (subs->fill_max)
+		subs->curpacksize = subs->maxpacksize;
 	else
-		strcpy(pcm->name, "USB Audio");
+		subs->curpacksize = maxsize;
 
-	snd_usb_init_substream(as, stream, fp);
+	if (snd_usb_get_speed(subs->dev) != USB_SPEED_FULL)
+		packs_per_ms = 8 >> subs->datainterval;
+	else
+		packs_per_ms = 1;
+
+	if (is_playback) {
+		urb_packs = max(chip->nrpacks, 1);
+		urb_packs = min(urb_packs, (unsigned int)MAX_PACKS);
+	} else
+		urb_packs = 1;
+	urb_packs *= packs_per_ms;
+	if (subs->syncpipe)
+		urb_packs = min(urb_packs, 1U << subs->syncinterval);
+
+	/* decide how many packets to be used */
+	if (is_playback) {
+		unsigned int minsize, maxpacks;
+		/* determine how small a packet can be */
+		minsize = (subs->freqn >> (16 - subs->datainterval))
+			  * (frame_bits >> 3);
+		/* with sync from device, assume it can be 12% lower */
+		if (subs->syncpipe)
+			minsize -= minsize >> 3;
+		minsize = max(minsize, 1u);
+		total_packs = (period_bytes + minsize - 1) / minsize;
+		/* we need at least two URBs for queueing */
+		if (total_packs < 2) {
+			total_packs = 2;
+		} else {
+			/* and we don't want too long a queue either */
+			maxpacks = max(MAX_QUEUE * packs_per_ms, urb_packs * 2);
+			total_packs = min(total_packs, maxpacks);
+		}
+	} else {
+		while (urb_packs > 1 && urb_packs * maxsize >= period_bytes)
+			urb_packs >>= 1;
+		total_packs = MAX_URBS * urb_packs;
+	}
+	subs->nurbs = (total_packs + urb_packs - 1) / urb_packs;
+	if (subs->nurbs > MAX_URBS) {
+		/* too much... */
+		subs->nurbs = MAX_URBS;
+		total_packs = MAX_URBS * urb_packs;
+	} else if (subs->nurbs < 2) {
+		/* too little - we need at least two packets
+		 * to ensure contiguous playback/capture
+		 */
+		subs->nurbs = 2;
+	}
 
-	list_add(&as->list, &chip->pcm_list);
-	chip->pcm_devs++;
+	/* allocate and initialize data urbs */
+	for (i = 0; i < subs->nurbs; i++) {
+		struct snd_urb_ctx *u = &subs->dataurb[i];
+		u->index = i;
+		u->subs = subs;
+		u->packets = (i + 1) * total_packs / subs->nurbs
+			- i * total_packs / subs->nurbs;
+		u->buffer_size = maxsize * u->packets;
+		if (subs->fmt_type == UAC_FORMAT_TYPE_II)
+			u->packets++; /* for transfer delimiter */
+		u->urb = usb_alloc_urb(u->packets, GFP_KERNEL);
+		if (!u->urb)
+			goto out_of_memory;
+		u->urb->transfer_buffer =
+			usb_alloc_coherent(subs->dev, u->buffer_size,
+					   GFP_KERNEL, &u->urb->transfer_dma);
+		if (!u->urb->transfer_buffer)
+			goto out_of_memory;
+		u->urb->pipe = subs->datapipe;
+		u->urb->transfer_flags = URB_ISO_ASAP | URB_NO_TRANSFER_DMA_MAP;
+		u->urb->interval = 1 << subs->datainterval;
+		u->urb->context = u;
+		u->urb->complete = snd_complete_urb;
+	}
+
+	if (subs->syncpipe) {
+		/* allocate and initialize sync urbs */
+		subs->syncbuf = usb_alloc_coherent(subs->dev, SYNC_URBS * 4,
+						 GFP_KERNEL, &subs->sync_dma);
+		if (!subs->syncbuf)
+			goto out_of_memory;
+		for (i = 0; i < SYNC_URBS; i++) {
+			struct snd_urb_ctx *u = &subs->syncurb[i];
+			u->index = i;
+			u->subs = subs;
+			u->packets = 1;
+			u->urb = usb_alloc_urb(1, GFP_KERNEL);
+			if (!u->urb)
+				goto out_of_memory;
+			u->urb->transfer_buffer = subs->syncbuf + i * 4;
+			u->urb->transfer_dma = subs->sync_dma + i * 4;
+			u->urb->transfer_buffer_length = 4;
+			u->urb->pipe = subs->syncpipe;
+			u->urb->transfer_flags = URB_ISO_ASAP |
+						 URB_NO_TRANSFER_DMA_MAP;
+			u->urb->number_of_packets = 1;
+			u->urb->interval = 1 << subs->syncinterval;
+			u->urb->context = u;
+			u->urb->complete = snd_complete_sync_urb;
+		}
+	}
+	return 0;
 
-	snd_usb_proc_pcm_format_add(as);
+out_of_memory:
+	snd_usb_release_substream_urbs(subs, 0);
+	return -ENOMEM;
+}
 
+/*
+ * prepare urb for full speed capture sync pipe
+ *
+ * fill the length and offset of each urb descriptor.
+ * the fixed 10.14 frequency is passed through the pipe.
+ */
+static int prepare_capture_sync_urb(struct snd_usb_substream *subs,
+				    struct snd_pcm_runtime *runtime,
+				    struct urb *urb)
+{
+	unsigned char *cp = urb->transfer_buffer;
+	struct snd_urb_ctx *ctx = urb->context;
+
+	urb->dev = ctx->subs->dev; /* we need to set this at each time */
+	urb->iso_frame_desc[0].length = 3;
+	urb->iso_frame_desc[0].offset = 0;
+	cp[0] = subs->freqn >> 2;
+	cp[1] = subs->freqn >> 10;
+	cp[2] = subs->freqn >> 18;
 	return 0;
 }
 
-static int parse_uac_endpoint_attributes(struct snd_usb_audio *chip,
-					 struct usb_host_interface *alts,
-					 int protocol, int iface_no)
+/*
+ * prepare urb for high speed capture sync pipe
+ *
+ * fill the length and offset of each urb descriptor.
+ * the fixed 12.13 frequency is passed as 16.16 through the pipe.
+ */
+static int prepare_capture_sync_urb_hs(struct snd_usb_substream *subs,
+				       struct snd_pcm_runtime *runtime,
+				       struct urb *urb)
 {
-	/* parsed with a v1 header here. that's ok as we only look at the
-	 * header first which is the same for both versions */
-	struct uac_iso_endpoint_descriptor *csep;
-	struct usb_interface_descriptor *altsd = get_iface_desc(alts);
-	int attributes = 0;
-
-	csep = snd_usb_find_desc(alts->endpoint[0].extra, alts->endpoint[0].extralen, NULL, USB_DT_CS_ENDPOINT);
-
-	/* Creamware Noah has this descriptor after the 2nd endpoint */
-	if (!csep && altsd->bNumEndpoints >= 2)
-		csep = snd_usb_find_desc(alts->endpoint[1].extra, alts->endpoint[1].extralen, NULL, USB_DT_CS_ENDPOINT);
-
-	if (!csep || csep->bLength < 7 ||
-	    csep->bDescriptorSubtype != UAC_EP_GENERAL) {
-		snd_printk(KERN_WARNING "%d:%u:%d : no or invalid"
-			   " class specific endpoint descriptor\n",
-			   chip->dev->devnum, iface_no,
-			   altsd->bAlternateSetting);
-		return 0;
-	}
+	unsigned char *cp = urb->transfer_buffer;
+	struct snd_urb_ctx *ctx = urb->context;
+
+	urb->dev = ctx->subs->dev; /* we need to set this at each time */
+	urb->iso_frame_desc[0].length = 4;
+	urb->iso_frame_desc[0].offset = 0;
+	cp[0] = subs->freqn;
+	cp[1] = subs->freqn >> 8;
+	cp[2] = subs->freqn >> 16;
+	cp[3] = subs->freqn >> 24;
+	return 0;
+}
 
-	if (protocol == UAC_VERSION_1) {
-		attributes = csep->bmAttributes;
-	} else {
-		struct uac2_iso_endpoint_descriptor *csep2 =
-			(struct uac2_iso_endpoint_descriptor *) csep;
+/*
+ * process after capture sync complete
+ * - nothing to do
+ */
+static int retire_capture_sync_urb(struct snd_usb_substream *subs,
+				   struct snd_pcm_runtime *runtime,
+				   struct urb *urb)
+{
+	return 0;
+}
 
-		attributes = csep->bmAttributes & UAC_EP_CS_ATTR_FILL_MAX;
+/*
+ * prepare urb for capture data pipe
+ *
+ * fill the offset and length of each descriptor.
+ *
+ * we use a temporary buffer to write the captured data.
+ * since the length of written data is determined by host, we cannot
+ * write onto the pcm buffer directly...  the data is thus copied
+ * later at complete callback to the global buffer.
+ */
+static int prepare_capture_urb(struct snd_usb_substream *subs,
+			       struct snd_pcm_runtime *runtime,
+			       struct urb *urb)
+{
+	int i, offs;
+	struct snd_urb_ctx *ctx = urb->context;
+
+	offs = 0;
+	urb->dev = ctx->subs->dev; /* we need to set this at each time */
+	for (i = 0; i < ctx->packets; i++) {
+		urb->iso_frame_desc[i].offset = offs;
+		urb->iso_frame_desc[i].length = subs->curpacksize;
+		offs += subs->curpacksize;
+	}
+	urb->transfer_buffer_length = offs;
+	urb->number_of_packets = ctx->packets;
+	return 0;
+}
 
-		/* emulate the endpoint attributes of a v1 device */
-		if (csep2->bmControls & UAC2_CONTROL_PITCH)
-			attributes |= UAC_EP_CS_ATTR_PITCH_CONTROL;
+/*
+ * process after capture complete
+ *
+ * copy the data from each desctiptor to the pcm buffer, and
+ * update the current position.
+ */
+static int retire_capture_urb(struct snd_usb_substream *subs,
+			      struct snd_pcm_runtime *runtime,
+			      struct urb *urb)
+{
+	unsigned long flags;
+	unsigned char *cp;
+	int i;
+	unsigned int stride, frames, bytes, oldptr;
+	int period_elapsed = 0;
+
+	stride = runtime->frame_bits >> 3;
+
+	for (i = 0; i < urb->number_of_packets; i++) {
+		cp = (unsigned char *)urb->transfer_buffer + urb->iso_frame_desc[i].offset;
+		if (urb->iso_frame_desc[i].status) {
+			snd_printd(KERN_ERR "frame %d active: %d\n", i, urb->iso_frame_desc[i].status);
+			// continue;
+		}
+		bytes = urb->iso_frame_desc[i].actual_length;
+		frames = bytes / stride;
+		if (!subs->txfr_quirk)
+			bytes = frames * stride;
+		if (bytes % (runtime->sample_bits >> 3) != 0) {
+#ifdef CONFIG_SND_DEBUG_VERBOSE
+			int oldbytes = bytes;
+#endif
+			bytes = frames * stride;
+			snd_printdd(KERN_ERR "Corrected urb data len. %d->%d\n",
+							oldbytes, bytes);
+		}
+		/* update the current pointer */
+		spin_lock_irqsave(&subs->lock, flags);
+		oldptr = subs->hwptr_done;
+		subs->hwptr_done += bytes;
+		if (subs->hwptr_done >= runtime->buffer_size * stride)
+			subs->hwptr_done -= runtime->buffer_size * stride;
+		frames = (bytes + (oldptr % stride)) / stride;
+		subs->transfer_done += frames;
+		if (subs->transfer_done >= runtime->period_size) {
+			subs->transfer_done -= runtime->period_size;
+			period_elapsed = 1;
+		}
+		spin_unlock_irqrestore(&subs->lock, flags);
+		/* copy a data chunk */
+		if (oldptr + bytes > runtime->buffer_size * stride) {
+			unsigned int bytes1 =
+					runtime->buffer_size * stride - oldptr;
+			memcpy(runtime->dma_area + oldptr, cp, bytes1);
+			memcpy(runtime->dma_area, cp + bytes1, bytes - bytes1);
+		} else {
+			memcpy(runtime->dma_area + oldptr, cp, bytes);
+		}
 	}
+	if (period_elapsed)
+		snd_pcm_period_elapsed(subs->pcm_substream);
+	return 0;
+}
 
-	return attributes;
+/*
+ * 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;
 }
 
-static struct uac2_input_terminal_descriptor *
-	snd_usb_find_input_terminal_descriptor(struct usb_host_interface *ctrl_iface,
-					       int terminal_id)
+
+/*
+ * prepare urb for playback sync pipe
+ *
+ * set up the offset and length to receive the current frequency.
+ */
+static int prepare_playback_sync_urb(struct snd_usb_substream *subs,
+				     struct snd_pcm_runtime *runtime,
+				     struct urb *urb)
 {
-	struct uac2_input_terminal_descriptor *term = NULL;
+	struct snd_urb_ctx *ctx = urb->context;
+
+	urb->dev = ctx->subs->dev; /* we need to set this at each time */
+	urb->iso_frame_desc[0].length = min(4u, ctx->subs->syncmaxsize);
+	urb->iso_frame_desc[0].offset = 0;
+	return 0;
+}
 
-	while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
-					       ctrl_iface->extralen,
-					       term, UAC_INPUT_TERMINAL))) {
-		if (term->bTerminalID == terminal_id)
-			return term;
+/*
+ * process after playback sync complete
+ *
+ * Full speed devices report feedback values in 10.14 format as samples per
+ * frame, high speed devices in 16.16 format as samples per microframe.
+ * Because the Audio Class 1 spec was written before USB 2.0, many high speed
+ * devices use a wrong interpretation, some others use an entirely different
+ * format.  Therefore, we cannot predict what format any particular device uses
+ * and must detect it automatically.
+ */
+static int retire_playback_sync_urb(struct snd_usb_substream *subs,
+				    struct snd_pcm_runtime *runtime,
+				    struct urb *urb)
+{
+	unsigned int f;
+	int shift;
+	unsigned long flags;
+
+	if (urb->iso_frame_desc[0].status != 0 ||
+	    urb->iso_frame_desc[0].actual_length < 3)
+		return 0;
+
+	f = le32_to_cpup(urb->transfer_buffer);
+	if (urb->iso_frame_desc[0].actual_length == 3)
+		f &= 0x00ffffff;
+	else
+		f &= 0x0fffffff;
+	if (f == 0)
+		return 0;
+
+	if (unlikely(subs->freqshift == INT_MIN)) {
+		/*
+		 * The first time we see a feedback value, determine its format
+		 * by shifting it left or right until it matches the nominal
+		 * frequency value.  This assumes that the feedback does not
+		 * differ from the nominal value more than +50% or -25%.
+		 */
+		shift = 0;
+		while (f < subs->freqn - subs->freqn / 4) {
+			f <<= 1;
+			shift++;
+		}
+		while (f > subs->freqn + subs->freqn / 2) {
+			f >>= 1;
+			shift--;
+		}
+		subs->freqshift = shift;
+	}
+	else if (subs->freqshift >= 0)
+		f <<= subs->freqshift;
+	else
+		f >>= -subs->freqshift;
+
+	if (likely(f >= subs->freqn - subs->freqn / 8 && f <= subs->freqmax)) {
+		/*
+		 * If the frequency looks valid, set it.
+		 * This value is referred to in prepare_playback_urb().
+		 */
+		spin_lock_irqsave(&subs->lock, flags);
+		subs->freqm = f;
+		spin_unlock_irqrestore(&subs->lock, flags);
+	} else {
+		/*
+		 * Out of range; maybe the shift value is wrong.
+		 * Reset it so that we autodetect again the next time.
+		 */
+		subs->freqshift = INT_MIN;
 	}
 
-	return NULL;
+	return 0;
 }
 
-static struct uac2_output_terminal_descriptor *
-	snd_usb_find_output_terminal_descriptor(struct usb_host_interface *ctrl_iface,
-						int terminal_id)
+/* determine the number of frames in the next packet */
+static int snd_usb_audio_next_packet_size(struct snd_usb_substream *subs)
 {
-	struct uac2_output_terminal_descriptor *term = NULL;
-
-	while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
-					       ctrl_iface->extralen,
-					       term, UAC_OUTPUT_TERMINAL))) {
-		if (term->bTerminalID == terminal_id)
-			return term;
+	if (subs->fill_max)
+		return subs->maxframesize;
+	else {
+		subs->phase = (subs->phase & 0xffff)
+			+ (subs->freqm << subs->datainterval);
+		return min(subs->phase >> 16, subs->maxframesize);
 	}
+}
 
-	return NULL;
+/*
+ * Prepare urb for streaming before playback starts or when paused.
+ *
+ * We don't have any data, so we send silence.
+ */
+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;
+	int stride = runtime->frame_bits >> 3;
+
+	offs = 0;
+	urb->dev = ctx->subs->dev;
+	for (i = 0; i < ctx->packets; ++i) {
+		counts = snd_usb_audio_next_packet_size(subs);
+		urb->iso_frame_desc[i].offset = offs * stride;
+		urb->iso_frame_desc[i].length = counts * stride;
+		offs += counts;
+	}
+	urb->number_of_packets = ctx->packets;
+	urb->transfer_buffer_length = offs * stride;
+	memset(urb->transfer_buffer,
+	       runtime->format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0,
+	       offs * stride);
+	return 0;
 }
 
-int snd_usb_parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
+/*
+ * prepare urb for playback data pipe
+ *
+ * Since a URB can handle only a single linear buffer, we must use double
+ * buffering when the data to be transferred overflows the buffer boundary.
+ * To avoid inconsistencies when updating hwptr_done, we use double buffering
+ * for all URBs.
+ */
+static int prepare_playback_urb(struct snd_usb_substream *subs,
+				struct snd_pcm_runtime *runtime,
+				struct urb *urb)
 {
-	struct usb_device *dev;
-	struct usb_interface *iface;
-	struct usb_host_interface *alts;
-	struct usb_interface_descriptor *altsd;
-	int i, altno, err, stream;
-	int format = 0, num_channels = 0;
-	struct audioformat *fp = NULL;
-	int num, protocol, clock = 0;
-	struct uac_format_type_i_continuous_descriptor *fmt;
+	int i, stride;
+	unsigned int counts, frames, bytes;
+	unsigned long flags;
+	int period_elapsed = 0;
+	struct snd_urb_ctx *ctx = urb->context;
+
+	stride = runtime->frame_bits >> 3;
+
+	frames = 0;
+	urb->dev = ctx->subs->dev; /* we need to set this at each time */
+	urb->number_of_packets = 0;
+	spin_lock_irqsave(&subs->lock, flags);
+	for (i = 0; i < ctx->packets; i++) {
+		counts = snd_usb_audio_next_packet_size(subs);
+		/* set up descriptor */
+		urb->iso_frame_desc[i].offset = frames * stride;
+		urb->iso_frame_desc[i].length = counts * stride;
+		frames += counts;
+		urb->number_of_packets++;
+		subs->transfer_done += counts;
+		if (subs->transfer_done >= runtime->period_size) {
+			subs->transfer_done -= runtime->period_size;
+			period_elapsed = 1;
+			if (subs->fmt_type == UAC_FORMAT_TYPE_II) {
+				if (subs->transfer_done > 0) {
+					/* FIXME: fill-max mode is not
+					 * supported yet */
+					frames -= subs->transfer_done;
+					counts -= subs->transfer_done;
+					urb->iso_frame_desc[i].length =
+						counts * stride;
+					subs->transfer_done = 0;
+				}
+				i++;
+				if (i < ctx->packets) {
+					/* add a transfer delimiter */
+					urb->iso_frame_desc[i].offset =
+						frames * stride;
+					urb->iso_frame_desc[i].length = 0;
+					urb->number_of_packets++;
+				}
+				break;
+			}
+		}
+		if (period_elapsed) /* finish at the period boundary */
+			break;
+	}
+	bytes = frames * stride;
+	if (subs->hwptr_done + bytes > runtime->buffer_size * stride) {
+		/* err, the transferred area goes over buffer boundary. */
+		unsigned int bytes1 =
+			runtime->buffer_size * stride - subs->hwptr_done;
+		memcpy(urb->transfer_buffer,
+		       runtime->dma_area + subs->hwptr_done, bytes1);
+		memcpy(urb->transfer_buffer + bytes1,
+		       runtime->dma_area, bytes - bytes1);
+	} else {
+		memcpy(urb->transfer_buffer,
+		       runtime->dma_area + subs->hwptr_done, bytes);
+	}
+	subs->hwptr_done += bytes;
+	if (subs->hwptr_done >= runtime->buffer_size * stride)
+		subs->hwptr_done -= runtime->buffer_size * stride;
+
+	/* update delay with exact number of samples queued */
+	runtime->delay = subs->last_delay;
+	runtime->delay += frames;
+	subs->last_delay = runtime->delay;
+
+	/* realign last_frame_number */
+	subs->last_frame_number = usb_get_current_frame_number(subs->dev);
+	subs->last_frame_number &= 0xFF; /* keep 8 LSBs */
+
+	spin_unlock_irqrestore(&subs->lock, flags);
+	urb->transfer_buffer_length = bytes;
+	if (period_elapsed)
+		snd_pcm_period_elapsed(subs->pcm_substream);
+	return 0;
+}
 
-	dev = chip->dev;
+/*
+ * process after playback data complete
+ * - decrease the delay count again
+ */
+static int retire_playback_urb(struct snd_usb_substream *subs,
+			       struct snd_pcm_runtime *runtime,
+			       struct urb *urb)
+{
+	unsigned long flags;
+	int stride = runtime->frame_bits >> 3;
+	int processed = urb->transfer_buffer_length / stride;
+	int est_delay;
 
-	/* parse the interface's altsettings */
-	iface = usb_ifnum_to_if(dev, iface_no);
+	spin_lock_irqsave(&subs->lock, flags);
 
-	num = iface->num_altsetting;
+	est_delay = snd_usb_pcm_delay(subs, runtime->rate);
+	/* update delay with exact number of samples played */
+	if (processed > subs->last_delay)
+		subs->last_delay = 0;
+	else
+		subs->last_delay -= processed;
+	runtime->delay = subs->last_delay;
 
 	/*
-	 * Dallas DS4201 workaround: It presents 5 altsettings, but the last
-	 * one misses syncpipe, and does not produce any sound.
+	 * Report when delay estimate is off by more than 2ms.
+	 * The error should be lower than 2ms since the estimate relies
+	 * on two reads of a counter updated every ms.
 	 */
-	if (chip->usb_id == USB_ID(0x04fa, 0x4201))
-		num = 4;
-
-	for (i = 0; i < num; i++) {
-		alts = &iface->altsetting[i];
-		altsd = get_iface_desc(alts);
-		protocol = altsd->bInterfaceProtocol;
-		/* skip invalid one */
-		if ((altsd->bInterfaceClass != USB_CLASS_AUDIO &&
-		     altsd->bInterfaceClass != USB_CLASS_VENDOR_SPEC) ||
-		    (altsd->bInterfaceSubClass != USB_SUBCLASS_AUDIOSTREAMING &&
-		     altsd->bInterfaceSubClass != USB_SUBCLASS_VENDOR_SPEC) ||
-		    altsd->bNumEndpoints < 1 ||
-		    le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize) == 0)
-			continue;
-		/* must be isochronous */
-		if ((get_endpoint(alts, 0)->bmAttributes & USB_ENDPOINT_XFERTYPE_MASK) !=
-		    USB_ENDPOINT_XFER_ISOC)
-			continue;
-		/* check direction */
-		stream = (get_endpoint(alts, 0)->bEndpointAddress & USB_DIR_IN) ?
-			SNDRV_PCM_STREAM_CAPTURE : SNDRV_PCM_STREAM_PLAYBACK;
-		altno = altsd->bAlternateSetting;
-
-		if (snd_usb_apply_interface_quirk(chip, iface_no, altno))
-			continue;
-
-		/* get audio formats */
-		switch (protocol) {
-		default:
-			snd_printdd(KERN_WARNING "%d:%u:%d: unknown interface protocol %#02x, assuming v1\n",
-				    dev->devnum, iface_no, altno, protocol);
-			protocol = UAC_VERSION_1;
-			/* fall through */
-
-		case UAC_VERSION_1: {
-			struct uac1_as_header_descriptor *as =
-				snd_usb_find_csint_desc(alts->extra, alts->extralen, NULL, UAC_AS_GENERAL);
-
-			if (!as) {
-				snd_printk(KERN_ERR "%d:%u:%d : UAC_AS_GENERAL descriptor not found\n",
-					   dev->devnum, iface_no, altno);
-				continue;
-			}
+	if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
+		snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
+			est_delay, subs->last_delay);
 
-			if (as->bLength < sizeof(*as)) {
-				snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
-					   dev->devnum, iface_no, altno);
-				continue;
-			}
+	spin_unlock_irqrestore(&subs->lock, flags);
+	return 0;
+}
 
-			format = le16_to_cpu(as->wFormatTag); /* remember the format value */
-			break;
-		}
+static const char *usb_error_string(int err)
+{
+	switch (err) {
+	case -ENODEV:
+		return "no device";
+	case -ENOENT:
+		return "endpoint not enabled";
+	case -EPIPE:
+		return "endpoint stalled";
+	case -ENOSPC:
+		return "not enough bandwidth";
+	case -ESHUTDOWN:
+		return "device disabled";
+	case -EHOSTUNREACH:
+		return "device suspended";
+	case -EINVAL:
+	case -EAGAIN:
+	case -EFBIG:
+	case -EMSGSIZE:
+		return "internal error";
+	default:
+		return "unknown error";
+	}
+}
 
-		case UAC_VERSION_2: {
-			struct uac2_input_terminal_descriptor *input_term;
-			struct uac2_output_terminal_descriptor *output_term;
-			struct uac2_as_header_descriptor *as =
-				snd_usb_find_csint_desc(alts->extra, alts->extralen, NULL, UAC_AS_GENERAL);
+/*
+ * set up and start data/sync urbs
+ */
+static int start_urbs(struct snd_usb_substream *subs, struct snd_pcm_runtime *runtime)
+{
+	unsigned int i;
+	int err;
 
-			if (!as) {
-				snd_printk(KERN_ERR "%d:%u:%d : UAC_AS_GENERAL descriptor not found\n",
-					   dev->devnum, iface_no, altno);
-				continue;
+	if (subs->stream->chip->shutdown)
+		return -EBADFD;
+
+	for (i = 0; i < subs->nurbs; i++) {
+		if (snd_BUG_ON(!subs->dataurb[i].urb))
+			return -EINVAL;
+		if (subs->ops.prepare(subs, runtime, subs->dataurb[i].urb) < 0) {
+			snd_printk(KERN_ERR "cannot prepare datapipe for urb %d\n", i);
+			goto __error;
+		}
+	}
+	if (subs->syncpipe) {
+		for (i = 0; i < SYNC_URBS; i++) {
+			if (snd_BUG_ON(!subs->syncurb[i].urb))
+				return -EINVAL;
+			if (subs->ops.prepare_sync(subs, runtime, subs->syncurb[i].urb) < 0) {
+				snd_printk(KERN_ERR "cannot prepare syncpipe for urb %d\n", i);
+				goto __error;
 			}
+		}
+	}
 
-			if (as->bLength < sizeof(*as)) {
-				snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
-					   dev->devnum, iface_no, altno);
-				continue;
+	subs->active_mask = 0;
+	subs->unlink_mask = 0;
+	subs->running = 1;
+	for (i = 0; i < subs->nurbs; i++) {
+		err = usb_submit_urb(subs->dataurb[i].urb, GFP_ATOMIC);
+		if (err < 0) {
+			snd_printk(KERN_ERR "cannot submit datapipe "
+				   "for urb %d, error %d: %s\n",
+				   i, err, usb_error_string(err));
+			goto __error;
+		}
+		set_bit(i, &subs->active_mask);
+	}
+	if (subs->syncpipe) {
+		for (i = 0; i < SYNC_URBS; i++) {
+			err = usb_submit_urb(subs->syncurb[i].urb, GFP_ATOMIC);
+			if (err < 0) {
+				snd_printk(KERN_ERR "cannot submit syncpipe "
+					   "for urb %d, error %d: %s\n",
+					   i, err, usb_error_string(err));
+				goto __error;
 			}
+			set_bit(i + 16, &subs->active_mask);
+		}
+	}
+	return 0;
 
-			num_channels = as->bNrChannels;
-			format = le32_to_cpu(as->bmFormats);
+ __error:
+	// snd_pcm_stop(subs->pcm_substream, SNDRV_PCM_STATE_XRUN);
+	deactivate_urbs(subs, 0, 0);
+	return -EPIPE;
+}
 
-			/* lookup the terminal associated to this interface
-			 * to extract the clock */
-			input_term = snd_usb_find_input_terminal_descriptor(chip->ctrl_intf,
-									    as->bTerminalLink);
-			if (input_term) {
-				clock = input_term->bCSourceID;
-				break;
-			}
 
-			output_term = snd_usb_find_output_terminal_descriptor(chip->ctrl_intf,
-									      as->bTerminalLink);
-			if (output_term) {
-				clock = output_term->bCSourceID;
-				break;
-			}
+/*
+ */
+static struct snd_urb_ops audio_urb_ops[2] = {
+	{
+		.prepare =	prepare_nodata_playback_urb,
+		.retire =	retire_playback_urb,
+		.prepare_sync =	prepare_playback_sync_urb,
+		.retire_sync =	retire_playback_sync_urb,
+	},
+	{
+		.prepare =	prepare_capture_urb,
+		.retire =	retire_capture_urb,
+		.prepare_sync =	prepare_capture_sync_urb,
+		.retire_sync =	retire_capture_sync_urb,
+	},
+};
 
-			snd_printk(KERN_ERR "%d:%u:%d : bogus bTerminalLink %d\n",
-				   dev->devnum, iface_no, altno, as->bTerminalLink);
-			continue;
-		}
-		}
+/*
+ * initialize the substream instance.
+ */
 
-		/* get format type */
-		fmt = snd_usb_find_csint_desc(alts->extra, alts->extralen, NULL, UAC_FORMAT_TYPE);
-		if (!fmt) {
-			snd_printk(KERN_ERR "%d:%u:%d : no UAC_FORMAT_TYPE desc\n",
-				   dev->devnum, iface_no, altno);
-			continue;
-		}
-		if (((protocol == UAC_VERSION_1) && (fmt->bLength < 8)) ||
-		    ((protocol == UAC_VERSION_2) && (fmt->bLength < 6))) {
-			snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_FORMAT_TYPE desc\n",
-				   dev->devnum, iface_no, altno);
-			continue;
-		}
+void snd_usb_init_substream(struct snd_usb_stream *as,
+			    int stream, struct audioformat *fp)
+{
+	struct snd_usb_substream *subs = &as->substream[stream];
+
+	INIT_LIST_HEAD(&subs->fmt_list);
+	spin_lock_init(&subs->lock);
+
+	subs->stream = as;
+	subs->direction = stream;
+	subs->dev = as->chip->dev;
+	subs->txfr_quirk = as->chip->txfr_quirk;
+	subs->ops = audio_urb_ops[stream];
+	if (snd_usb_get_speed(subs->dev) >= USB_SPEED_HIGH)
+		subs->ops.prepare_sync = prepare_capture_sync_urb_hs;
+
+	snd_usb_set_pcm_ops(as->pcm, stream);
+
+	list_add_tail(&fp->list, &subs->fmt_list);
+	subs->formats |= fp->formats;
+	subs->endpoint = fp->endpoint;
+	subs->num_formats++;
+	subs->fmt_type = fp->fmt_type;
+}
 
-		/*
-		 * Blue Microphones workaround: The last altsetting is identical
-		 * with the previous one, except for a larger packet size, but
-		 * is actually a mislabeled two-channel setting; ignore it.
-		 */
-		if (fmt->bNrChannels == 1 &&
-		    fmt->bSubframeSize == 2 &&
-		    altno == 2 && num == 3 &&
-		    fp && fp->altsetting == 1 && fp->channels == 1 &&
-		    fp->formats == SNDRV_PCM_FMTBIT_S16_LE &&
-		    protocol == UAC_VERSION_1 &&
-		    le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize) ==
-							fp->maxpacksize * 2)
-			continue;
-
-		fp = kzalloc(sizeof(*fp), GFP_KERNEL);
-		if (! fp) {
-			snd_printk(KERN_ERR "cannot malloc\n");
-			return -ENOMEM;
-		}
+int snd_usb_substream_playback_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct snd_usb_substream *subs = substream->runtime->private_data;
 
-		fp->iface = iface_no;
-		fp->altsetting = altno;
-		fp->altset_idx = i;
-		fp->endpoint = get_endpoint(alts, 0)->bEndpointAddress;
-		fp->ep_attr = get_endpoint(alts, 0)->bmAttributes;
-		fp->datainterval = snd_usb_parse_datainterval(chip, alts);
-		fp->maxpacksize = le16_to_cpu(get_endpoint(alts, 0)->wMaxPacketSize);
-		/* num_channels is only set for v2 interfaces */
-		fp->channels = num_channels;
-		if (snd_usb_get_speed(dev) == USB_SPEED_HIGH)
-			fp->maxpacksize = (((fp->maxpacksize >> 11) & 3) + 1)
-					* (fp->maxpacksize & 0x7ff);
-		fp->attributes = parse_uac_endpoint_attributes(chip, alts, protocol, iface_no);
-		fp->clock = clock;
-
-		/* some quirks for attributes here */
-
-		switch (chip->usb_id) {
-		case USB_ID(0x0a92, 0x0053): /* AudioTrak Optoplay */
-			/* Optoplay sets the sample rate attribute although
-			 * it seems not supporting it in fact.
-			 */
-			fp->attributes &= ~UAC_EP_CS_ATTR_SAMPLE_RATE;
-			break;
-		case USB_ID(0x041e, 0x3020): /* Creative SB Audigy 2 NX */
-		case USB_ID(0x0763, 0x2003): /* M-Audio Audiophile USB */
-			/* doesn't set the sample rate attribute, but supports it */
-			fp->attributes |= UAC_EP_CS_ATTR_SAMPLE_RATE;
-			break;
-		case USB_ID(0x0763, 0x2001):  /* M-Audio Quattro USB */
-		case USB_ID(0x0763, 0x2012):  /* M-Audio Fast Track Pro USB */
-		case USB_ID(0x047f, 0x0ca1): /* plantronics headset */
-		case USB_ID(0x077d, 0x07af): /* Griffin iMic (note that there is
-						an older model 77d:223) */
-		/*
-		 * plantronics headset and Griffin iMic have set adaptive-in
-		 * although it's really not...
-		 */
-			fp->ep_attr &= ~USB_ENDPOINT_SYNCTYPE;
-			if (stream == SNDRV_PCM_STREAM_PLAYBACK)
-				fp->ep_attr |= USB_ENDPOINT_SYNC_ADAPTIVE;
-			else
-				fp->ep_attr |= USB_ENDPOINT_SYNC_SYNC;
-			break;
-		}
+	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;
+	}
 
-		/* ok, let's parse further... */
-		if (snd_usb_parse_audio_format(chip, fp, format, fmt, stream, alts) < 0) {
-			kfree(fp->rate_table);
-			kfree(fp);
-			fp = NULL;
-			continue;
-		}
+	return -EINVAL;
+}
 
-		snd_printdd(KERN_INFO "%d:%u:%d: add audio endpoint %#x\n", dev->devnum, iface_no, altno, fp->endpoint);
-		err = snd_usb_add_audio_endpoint(chip, stream, fp);
-		if (err < 0) {
-			kfree(fp->rate_table);
-			kfree(fp);
-			return err;
-		}
-		/* try to set the interface... */
-		usb_set_interface(chip->dev, iface_no, altno);
-		snd_usb_init_pitch(chip, iface_no, alts, fp);
-		snd_usb_init_sample_rate(chip, iface_no, alts, fp, fp->rate_max);
+int snd_usb_substream_capture_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct snd_usb_substream *subs = substream->runtime->private_data;
+
+	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;
 	}
+
+	return -EINVAL;
+}
+
+int snd_usb_substream_prepare(struct snd_usb_substream *subs,
+			      struct snd_pcm_runtime *runtime)
+{
+	/* clear urbs (to be sure) */
+	deactivate_urbs(subs, 0, 1);
+	wait_clear_urbs(subs);
+
+	/* 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_nodata_playback_urb;
+		return start_urbs(subs, runtime);
+	}
+
 	return 0;
 }