sound/usb/endpoint.c - kernel/msm-4.9 - Gitiles

 /*
  *   This program is free software; you can redistribute it and/or modify
  *   it under the terms of the GNU General Public License as published by
  *   the Free Software Foundation; either version 2 of the License, or
  *   (at your option) any later version.
  *
  *   This program is distributed in the hope that it will be useful,
  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *   GNU General Public License for more details.
  *
  *   You should have received a copy of the GNU General Public License
  *   along with this program; if not, write to the Free Software
  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
  *
  */

 #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 "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
  */
 static void free_substream(struct snd_usb_substream *subs)
 {
 	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);
 }


 /*
  * free a usb stream instance
  */
 static void snd_usb_audio_stream_free(struct snd_usb_stream *stream)
 {
 	free_substream(&stream->substream[0]);
 	free_substream(&stream->substream[1]);
 	list_del(&stream->list);
 	kfree(stream);
 }

 static void snd_usb_audio_pcm_free(struct snd_pcm *pcm)
 {
 	struct snd_usb_stream *stream = pcm->private_data;
 	if (stream) {
 		stream->pcm = NULL;
 		snd_usb_audio_stream_free(stream);
 	}
 }


 /*
  * 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.
  */
 int snd_usb_add_audio_endpoint(struct snd_usb_audio *chip, int stream, struct audioformat *fp)
 {
 	struct list_head *p;
 	struct snd_usb_stream *as;
 	struct snd_usb_substream *subs;
 	struct snd_pcm *pcm;
 	int err;

 	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;
 		}
 	}
 	/* 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;
 	}

 	/* 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;
 	}
 	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);
 	else
 		strcpy(pcm->name, "USB Audio");

 	snd_usb_init_substream(as, stream, fp);

 	list_add(&as->list, &chip->pcm_list);
 	chip->pcm_devs++;

 	snd_usb_proc_pcm_format_add(as);

 	return 0;
 }

 static int parse_uac_endpoint_attributes(struct snd_usb_audio *chip,
 					 struct usb_host_interface *alts,
 					 int protocol, int iface_no)
 {
 	/* 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;
 	}

 	if (protocol == UAC_VERSION_1) {
 		attributes = csep->bmAttributes;
 	} else {
 		struct uac2_iso_endpoint_descriptor *csep2 =
 			(struct uac2_iso_endpoint_descriptor *) csep;

 		attributes = csep->bmAttributes & UAC_EP_CS_ATTR_FILL_MAX;

 		/* emulate the endpoint attributes of a v1 device */
 		if (csep2->bmControls & UAC2_CONTROL_PITCH)
 			attributes |= UAC_EP_CS_ATTR_PITCH_CONTROL;
 	}

 	return attributes;
 }

 static struct uac2_input_terminal_descriptor *
 	snd_usb_find_input_terminal_descriptor(struct usb_host_interface *ctrl_iface,
 					       int terminal_id)
 {
 	struct uac2_input_terminal_descriptor *term = NULL;

 	while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
 					       ctrl_iface->extralen,
 					       term, UAC_INPUT_TERMINAL))) {
 		if (term->bTerminalID == terminal_id)
 			return term;
 	}

 	return NULL;
 }

 static struct uac2_output_terminal_descriptor *
 	snd_usb_find_output_terminal_descriptor(struct usb_host_interface *ctrl_iface,
 						int terminal_id)
 {
 	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;
 	}

 	return NULL;
 }

 int snd_usb_parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
 {
 	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;

 	dev = chip->dev;

 	/* parse the interface's altsettings */
 	iface = usb_ifnum_to_if(dev, iface_no);

 	num = iface->num_altsetting;

 	/*
 	 * Dallas DS4201 workaround: It presents 5 altsettings, but the last
 	 * one misses syncpipe, and does not produce any sound.
 	 */
 	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) {
 		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 (as->bLength < sizeof(*as)) {
 				snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
 					   dev->devnum, iface_no, altno);
 				continue;
 			}

 			format = le16_to_cpu(as->wFormatTag); /* remember the format value */
 			break;
 		}

 		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);

 			if (!as) {
 				snd_printk(KERN_ERR "%d:%u:%d : UAC_AS_GENERAL descriptor not found\n",
 					   dev->devnum, iface_no, altno);
 				continue;
 			}

 			if (as->bLength < sizeof(*as)) {
 				snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
 					   dev->devnum, iface_no, altno);
 				continue;
 			}

 			num_channels = as->bNrChannels;
 			format = le32_to_cpu(as->bmFormats);

 			/* 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;
 			}

 			snd_printk(KERN_ERR "%d:%u:%d : bogus bTerminalLink %d\n",
 				   dev->devnum, iface_no, altno, as->bTerminalLink);
 			continue;
 		}

 		default:
 			snd_printk(KERN_ERR "%d:%u:%d : unknown interface protocol %04x\n",
 				   dev->devnum, iface_no, altno, protocol);
 			continue;
 		}

 		/* 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;
 		}

 		/*
 		 * 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;
 		}

 		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 */
 		case USB_ID(0x0763, 0x2080): /* M-Audio Fast Track Ultra 8 */
 		case USB_ID(0x0763, 0x2081): /* M-Audio Fast Track Ultra 8R */
 			/* doesn't set the sample rate attribute, but supports it */
 			fp->attributes |= UAC_EP_CS_ATTR_SAMPLE_RATE;
 			break;
 		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;
 		}

 		/* 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;
 		}

 		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);
 	}
 	return 0;
 }
	/*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License as published by
	* the Free Software Foundation; either version 2 of the License, or
	* (at your option) any later version.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program; if not, write to the Free Software
	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	*
	*/

	#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 "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
	*/
	static void free_substream(struct snd_usb_substream *subs)
	{
	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);
	}


	/*
	* free a usb stream instance
	*/
	static void snd_usb_audio_stream_free(struct snd_usb_stream *stream)
	{
	free_substream(&stream->substream[0]);
	free_substream(&stream->substream[1]);
	list_del(&stream->list);
	kfree(stream);
	}

	static void snd_usb_audio_pcm_free(struct snd_pcm *pcm)
	{
	struct snd_usb_stream *stream = pcm->private_data;
	if (stream) {
	stream->pcm = NULL;
	snd_usb_audio_stream_free(stream);
	}
	}


	/*
	* 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.
	*/
	int snd_usb_add_audio_endpoint(struct snd_usb_audio chip, int stream, struct audioformat fp)
	{
	struct list_head *p;
	struct snd_usb_stream *as;
	struct snd_usb_substream *subs;
	struct snd_pcm *pcm;
	int err;

	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;
	}
	}
	/* 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;
	}

	/* 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;
	}
	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);
	else
	strcpy(pcm->name, "USB Audio");

	snd_usb_init_substream(as, stream, fp);

	list_add(&as->list, &chip->pcm_list);
	chip->pcm_devs++;

	snd_usb_proc_pcm_format_add(as);

	return 0;
	}

	static int parse_uac_endpoint_attributes(struct snd_usb_audio *chip,
	struct usb_host_interface *alts,
	int protocol, int iface_no)
	{
	/* 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;
	}

	if (protocol == UAC_VERSION_1) {
	attributes = csep->bmAttributes;
	} else {
	struct uac2_iso_endpoint_descriptor *csep2 =
	(struct uac2_iso_endpoint_descriptor *) csep;

	attributes = csep->bmAttributes & UAC_EP_CS_ATTR_FILL_MAX;

	/* emulate the endpoint attributes of a v1 device */
	if (csep2->bmControls & UAC2_CONTROL_PITCH)
	attributes \|= UAC_EP_CS_ATTR_PITCH_CONTROL;
	}

	return attributes;
	}

	static struct uac2_input_terminal_descriptor *
	snd_usb_find_input_terminal_descriptor(struct usb_host_interface *ctrl_iface,
	int terminal_id)
	{
	struct uac2_input_terminal_descriptor *term = NULL;

	while ((term = snd_usb_find_csint_desc(ctrl_iface->extra,
	ctrl_iface->extralen,
	term, UAC_INPUT_TERMINAL))) {
	if (term->bTerminalID == terminal_id)
	return term;
	}

	return NULL;
	}

	static struct uac2_output_terminal_descriptor *
	snd_usb_find_output_terminal_descriptor(struct usb_host_interface *ctrl_iface,
	int terminal_id)
	{
	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;
	}

	return NULL;
	}

	int snd_usb_parse_audio_endpoints(struct snd_usb_audio *chip, int iface_no)
	{
	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;

	dev = chip->dev;

	/* parse the interface's altsettings */
	iface = usb_ifnum_to_if(dev, iface_no);

	num = iface->num_altsetting;

	/*
	* Dallas DS4201 workaround: It presents 5 altsettings, but the last
	* one misses syncpipe, and does not produce any sound.
	*/
	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) {
	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 (as->bLength < sizeof(*as)) {
	snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
	dev->devnum, iface_no, altno);
	continue;
	}

	format = le16_to_cpu(as->wFormatTag); /* remember the format value */
	break;
	}

	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);

	if (!as) {
	snd_printk(KERN_ERR "%d:%u:%d : UAC_AS_GENERAL descriptor not found\n",
	dev->devnum, iface_no, altno);
	continue;
	}

	if (as->bLength < sizeof(*as)) {
	snd_printk(KERN_ERR "%d:%u:%d : invalid UAC_AS_GENERAL desc\n",
	dev->devnum, iface_no, altno);
	continue;
	}

	num_channels = as->bNrChannels;
	format = le32_to_cpu(as->bmFormats);

	/* 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;
	}

	snd_printk(KERN_ERR "%d:%u:%d : bogus bTerminalLink %d\n",
	dev->devnum, iface_no, altno, as->bTerminalLink);
	continue;
	}

	default:
	snd_printk(KERN_ERR "%d:%u:%d : unknown interface protocol %04x\n",
	dev->devnum, iface_no, altno, protocol);
	continue;
	}

	/* 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;
	}

	/*
	* 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;
	}

	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 */
	case USB_ID(0x0763, 0x2080): /* M-Audio Fast Track Ultra 8 */
	case USB_ID(0x0763, 0x2081): /* M-Audio Fast Track Ultra 8R */
	/* doesn't set the sample rate attribute, but supports it */
	fp->attributes \|= UAC_EP_CS_ATTR_SAMPLE_RATE;
	break;
	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;
	}

	/* 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;
	}

	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);
	}
	return 0;
	}