sound/usb/implicit.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 //
 // Special handling for implicit feedback mode
 //

 #include <linux/init.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 <sound/pcm_params.h>

 #include "usbaudio.h"
 #include "card.h"
 #include "helper.h"
 #include "implicit.h"

 enum {
 	IMPLICIT_FB_NONE,
 	IMPLICIT_FB_GENERIC,
 	IMPLICIT_FB_FIXED,
 	IMPLICIT_FB_BOTH,	/* generic playback + capture (for BOSS) */
 };

 struct snd_usb_implicit_fb_match {
 	unsigned int id;
 	unsigned int iface_class;
 	unsigned int ep_num;
 	unsigned int iface;
 	int type;
 };

 #define IMPLICIT_FB_GENERIC_DEV(vend, prod) \
 	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_GENERIC }
 #define IMPLICIT_FB_FIXED_DEV(vend, prod, ep, ifnum) \
 	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_FIXED, .ep_num = (ep),\
 	    .iface = (ifnum) }
 #define IMPLICIT_FB_BOTH_DEV(vend, prod, ep, ifnum) \
 	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_BOTH, .ep_num = (ep),\
 	    .iface = (ifnum) }
 #define IMPLICIT_FB_SKIP_DEV(vend, prod) \
 	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_NONE }

 /* Implicit feedback quirk table for playback */
 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(0x0763, 0x2080, 0x81, 2), /* M-Audio FastTrack Ultra */
 	IMPLICIT_FB_FIXED_DEV(0x0763, 0x2081, 0x81, 2), /* M-Audio FastTrack Ultra */
 	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+ */
 	IMPLICIT_FB_FIXED_DEV(0x0499, 0x172f, 0x81, 2), /* Steinberg UR22C */
 	IMPLICIT_FB_FIXED_DEV(0x0d9a, 0x00df, 0x81, 2), /* RTX6001 */
 	IMPLICIT_FB_FIXED_DEV(0x22f0, 0x0006, 0x81, 3), /* Allen&Heath Qu-16 */
 	IMPLICIT_FB_FIXED_DEV(0x1686, 0xf029, 0x82, 2), /* Zoom UAC-2 */
 	IMPLICIT_FB_FIXED_DEV(0x2466, 0x8003, 0x86, 2), /* Fractal Audio Axe-Fx II */
 	IMPLICIT_FB_FIXED_DEV(0x0499, 0x172a, 0x86, 2), /* Yamaha MODX */

 	/* Special matching */
 	{ .id = USB_ID(0x07fd, 0x0004), .iface_class = USB_CLASS_AUDIO,
 	  .type = IMPLICIT_FB_NONE },		/* MicroBook IIc */
 	/* ep = 0x84, ifnum = 0 */
 	{ .id = USB_ID(0x07fd, 0x0004), .iface_class = USB_CLASS_VENDOR_SPEC,
 	  .type = IMPLICIT_FB_FIXED,
 	  .ep_num = 0x84, .iface = 0 },		/* MOTU MicroBook II */

 	{} /* terminator */
 };

 /* Implicit feedback quirk table for capture: only FIXED type */
 static const struct snd_usb_implicit_fb_match capture_implicit_fb_quirks[] = {
 	{} /* terminator */
 };

 /* set up sync EP information on the audioformat */
 static int add_implicit_fb_sync_ep(struct snd_usb_audio *chip,
 				   struct audioformat *fmt,
 				   int ep, int ep_idx, int ifnum,
 				   const struct usb_host_interface *alts)
 {
 	struct usb_interface *iface;

 	if (!alts) {
 		iface = usb_ifnum_to_if(chip->dev, ifnum);
 		if (!iface || iface->num_altsetting < 2)
 			return 0;
 		alts = &iface->altsetting[1];
 	}

 	fmt->sync_ep = ep;
 	fmt->sync_iface = ifnum;
 	fmt->sync_altsetting = alts->desc.bAlternateSetting;
 	fmt->sync_ep_idx = ep_idx;
 	fmt->implicit_fb = 1;
 	usb_audio_dbg(chip,
 		      "%d:%d: added %s implicit_fb sync_ep %x, iface %d:%d\n",
 		      fmt->iface, fmt->altsetting,
 		      (ep & USB_DIR_IN) ? "playback" : "capture",
 		      fmt->sync_ep, fmt->sync_iface, fmt->sync_altsetting);
 	return 1;
 }

 /* Check whether the given UAC2 iface:altset points to an implicit fb source */
 static int add_generic_uac2_implicit_fb(struct snd_usb_audio *chip,
 					struct audioformat *fmt,
 					unsigned int ifnum,
 					unsigned int altsetting)
 {
 	struct usb_host_interface *alts;
 	struct usb_endpoint_descriptor *epd;

 	alts = snd_usb_get_host_interface(chip, ifnum, altsetting);
 	if (!alts)
 		return 0;
 	if (alts->desc.bInterfaceClass != USB_CLASS_AUDIO ||
 	    alts->desc.bInterfaceSubClass != USB_SUBCLASS_AUDIOSTREAMING ||
 	    alts->desc.bInterfaceProtocol != UAC_VERSION_2 ||
 	    alts->desc.bNumEndpoints < 1)
 		return 0;
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_in(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
 					USB_ENDPOINT_USAGE_IMPLICIT_FB)
 		return 0;
 	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
 				       ifnum, alts);
 }

 static bool roland_sanity_check_iface(struct usb_host_interface *alts)
 {
 	if (alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC ||
 	    (alts->desc.bInterfaceSubClass != 2 &&
 	     alts->desc.bInterfaceProtocol != 2) ||
 	    alts->desc.bNumEndpoints < 1)
 		return false;
 	return true;
 }

 /* Like the UAC2 case above, but specific to Roland with vendor class and hack */
 static int add_roland_implicit_fb(struct snd_usb_audio *chip,
 				  struct audioformat *fmt,
 				  struct usb_host_interface *alts)
 {
 	struct usb_endpoint_descriptor *epd;

 	if (!roland_sanity_check_iface(alts))
 		return 0;
 	/* only when both streams are with ASYNC type */
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_out(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return 0;

 	/* check capture EP */
 	alts = snd_usb_get_host_interface(chip,
 					  alts->desc.bInterfaceNumber + 1,
 					  alts->desc.bAlternateSetting);
 	if (!alts || !roland_sanity_check_iface(alts))
 		return 0;
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_in(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return 0;
 	chip->quirk_flags |= QUIRK_FLAG_PLAYBACK_FIRST;
 	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
 				       alts->desc.bInterfaceNumber, alts);
 }

 /* capture quirk for Roland device; always full-duplex */
 static int add_roland_capture_quirk(struct snd_usb_audio *chip,
 				    struct audioformat *fmt,
 				    struct usb_host_interface *alts)
 {
 	struct usb_endpoint_descriptor *epd;

 	if (!roland_sanity_check_iface(alts))
 		return 0;
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_in(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return 0;

 	alts = snd_usb_get_host_interface(chip,
 					  alts->desc.bInterfaceNumber - 1,
 					  alts->desc.bAlternateSetting);
 	if (!alts || !roland_sanity_check_iface(alts))
 		return 0;
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_out(epd))
 		return 0;
 	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
 				       alts->desc.bInterfaceNumber, alts);
 }

 /* Playback and capture EPs on Pioneer devices share the same iface/altset
  * for the implicit feedback operation
  */
 static bool is_pioneer_implicit_fb(struct snd_usb_audio *chip,
 				   struct usb_host_interface *alts)

 {
 	struct usb_endpoint_descriptor *epd;

 	if (USB_ID_VENDOR(chip->usb_id) != 0x2b73 &&
 	    USB_ID_VENDOR(chip->usb_id) != 0x08e4)
 		return false;
 	if (alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC)
 		return false;
 	if (alts->desc.bNumEndpoints != 2)
 		return false;

 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_out(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return false;

 	epd = get_endpoint(alts, 1);
 	if (!usb_endpoint_is_isoc_in(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC ||
 	    ((epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
 	     USB_ENDPOINT_USAGE_DATA &&
 	     (epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
 	     USB_ENDPOINT_USAGE_IMPLICIT_FB))
 		return false;

 	return true;
 }

 static int __add_generic_implicit_fb(struct snd_usb_audio *chip,
 				     struct audioformat *fmt,
 				     int iface, int altset)
 {
 	struct usb_host_interface *alts;
 	struct usb_endpoint_descriptor *epd;

 	alts = snd_usb_get_host_interface(chip, iface, altset);
 	if (!alts)
 		return 0;

 	if ((alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC &&
 	     alts->desc.bInterfaceClass != USB_CLASS_AUDIO) ||
 	    alts->desc.bNumEndpoints < 1)
 		return 0;
 	epd = get_endpoint(alts, 0);
 	if (!usb_endpoint_is_isoc_in(epd) ||
 	    (epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return 0;
 	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
 				       iface, alts);
 }

 /* More generic quirk: look for the sync EP next to the data EP */
 static int add_generic_implicit_fb(struct snd_usb_audio *chip,
 				   struct audioformat *fmt,
 				   struct usb_host_interface *alts)
 {
 	if ((fmt->ep_attr & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
 		return 0;

 	if (__add_generic_implicit_fb(chip, fmt,
 				      alts->desc.bInterfaceNumber + 1,
 				      alts->desc.bAlternateSetting))
 		return 1;
 	return __add_generic_implicit_fb(chip, fmt,
 					 alts->desc.bInterfaceNumber - 1,
 					 alts->desc.bAlternateSetting);
 }

 static const struct snd_usb_implicit_fb_match *
 find_implicit_fb_entry(struct snd_usb_audio *chip,
 		       const struct snd_usb_implicit_fb_match *match,
 		       const struct usb_host_interface *alts)
 {
 	for (; match->id; match++)
 		if (match->id == chip->usb_id &&
 		    (!match->iface_class ||
 		     (alts->desc.bInterfaceClass == match->iface_class)))
 			return match;

 	return NULL;
 }

 /* Setup an implicit feedback endpoint from a quirk. Returns 0 if no quirk
  * applies. Returns 1 if a quirk was found.
  */
 static int audioformat_implicit_fb_quirk(struct snd_usb_audio *chip,
 					 struct audioformat *fmt,
 					 struct usb_host_interface *alts)
 {
 	const struct snd_usb_implicit_fb_match *p;
 	unsigned int attr = fmt->ep_attr & USB_ENDPOINT_SYNCTYPE;

 	p = find_implicit_fb_entry(chip, playback_implicit_fb_quirks, alts);
 	if (p) {
 		switch (p->type) {
 		case IMPLICIT_FB_GENERIC:
 			return add_generic_implicit_fb(chip, fmt, alts);
 		case IMPLICIT_FB_NONE:
 			return 0; /* No quirk */
 		case IMPLICIT_FB_FIXED:
 			return add_implicit_fb_sync_ep(chip, fmt, p->ep_num, 0,
 						       p->iface, NULL);
 		}
 	}

 	/* Special handling for devices with capture quirks */
 	p = find_implicit_fb_entry(chip, capture_implicit_fb_quirks, alts);
 	if (p) {
 		switch (p->type) {
 		case IMPLICIT_FB_FIXED:
 			return 0; /* no quirk */
 		case IMPLICIT_FB_BOTH:
 			chip->quirk_flags |= QUIRK_FLAG_PLAYBACK_FIRST;
 			return add_generic_implicit_fb(chip, fmt, alts);
 		}
 	}

 	/* Generic UAC2 implicit feedback */
 	if (attr == USB_ENDPOINT_SYNC_ASYNC &&
 	    alts->desc.bInterfaceClass == USB_CLASS_AUDIO &&
 	    alts->desc.bInterfaceProtocol == UAC_VERSION_2 &&
 	    alts->desc.bNumEndpoints == 1) {
 		if (add_generic_uac2_implicit_fb(chip, fmt,
 						 alts->desc.bInterfaceNumber + 1,
 						 alts->desc.bAlternateSetting))
 			return 1;
 	}

 	/* Roland/BOSS implicit feedback with vendor spec class */
 	if (USB_ID_VENDOR(chip->usb_id) == 0x0582) {
 		if (add_roland_implicit_fb(chip, fmt, alts) > 0)
 			return 1;
 	}

 	/* Pioneer devices with vendor spec class */
 	if (is_pioneer_implicit_fb(chip, alts)) {
 		chip->quirk_flags |= QUIRK_FLAG_PLAYBACK_FIRST;
 		return add_implicit_fb_sync_ep(chip, fmt,
 					       get_endpoint(alts, 1)->bEndpointAddress,
 					       1, alts->desc.bInterfaceNumber,
 					       alts);
 	}

 	/* Try the generic implicit fb if available */
 	if (chip->generic_implicit_fb ||
 	    (chip->quirk_flags & QUIRK_FLAG_GENERIC_IMPLICIT_FB))
 		return add_generic_implicit_fb(chip, fmt, alts);

 	/* No quirk */
 	return 0;
 }

 /* same for capture, but only handling FIXED entry */
 static int audioformat_capture_quirk(struct snd_usb_audio *chip,
 				     struct audioformat *fmt,
 				     struct usb_host_interface *alts)
 {
 	const struct snd_usb_implicit_fb_match *p;

 	p = find_implicit_fb_entry(chip, capture_implicit_fb_quirks, alts);
 	if (p && (p->type == IMPLICIT_FB_FIXED || p->type == IMPLICIT_FB_BOTH))
 		return add_implicit_fb_sync_ep(chip, fmt, p->ep_num, 0,
 					       p->iface, NULL);

 	/* Roland/BOSS need full-duplex streams */
 	if (USB_ID_VENDOR(chip->usb_id) == 0x0582) {
 		if (add_roland_capture_quirk(chip, fmt, alts) > 0)
 			return 1;
 	}

 	if (is_pioneer_implicit_fb(chip, alts))
 		return 1; /* skip the quirk, also don't handle generic sync EP */
 	return 0;
 }

 /*
  * Parse altset and set up implicit feedback endpoint on the audioformat
  */
 int snd_usb_parse_implicit_fb_quirk(struct snd_usb_audio *chip,
 				    struct audioformat *fmt,
 				    struct usb_host_interface *alts)
 {
 	if (chip->quirk_flags & QUIRK_FLAG_SKIP_IMPLICIT_FB)
 		return 0;
 	if (fmt->endpoint & USB_DIR_IN)
 		return audioformat_capture_quirk(chip, fmt, alts);
 	else
 		return audioformat_implicit_fb_quirk(chip, fmt, alts);
 }

 /*
  * Return the score of matching two audioformats.
  * Veto the audioformat if:
  * - It has no channels for some reason.
  * - Requested PCM format is not supported.
  * - Requested sample rate is not supported.
  */
 static int match_endpoint_audioformats(struct snd_usb_substream *subs,
 				       const struct audioformat *fp,
 				       int rate, int channels,
 				       snd_pcm_format_t pcm_format)
 {
 	int i, score;

 	if (fp->channels < 1)
 		return 0;

 	if (!(fp->formats & pcm_format_to_bits(pcm_format)))
 		return 0;

 	if (fp->rates & SNDRV_PCM_RATE_CONTINUOUS) {
 		if (rate < fp->rate_min || rate > fp->rate_max)
 			return 0;
 	} else {
 		for (i = 0; i < fp->nr_rates; i++) {
 			if (fp->rate_table[i] == rate)
 				break;
 		}
 		if (i >= fp->nr_rates)
 			return 0;
 	}

 	score = 1;
 	if (fp->channels == channels)
 		score++;

 	return score;
 }

 static struct snd_usb_substream *
 find_matching_substream(struct snd_usb_audio *chip, int stream, int ep_num,
 			int fmt_type)
 {
 	struct snd_usb_stream *as;
 	struct snd_usb_substream *subs;

 	list_for_each_entry(as, &chip->pcm_list, list) {
 		subs = &as->substream[stream];
 		if (as->fmt_type == fmt_type && subs->ep_num == ep_num)
 			return subs;
 	}

 	return NULL;
 }

 /*
  * Return the audioformat that is suitable for the implicit fb
  */
 const struct audioformat *
 snd_usb_find_implicit_fb_sync_format(struct snd_usb_audio *chip,
 				     const struct audioformat *target,
 				     const struct snd_pcm_hw_params *params,
 				     int stream)
 {
 	struct snd_usb_substream *subs;
 	const struct audioformat *fp, *sync_fmt = NULL;
 	int score, high_score;

 	/* Use the original audioformat as fallback for the shared altset */
 	if (target->iface == target->sync_iface &&
 	    target->altsetting == target->sync_altsetting)
 		sync_fmt = target;

 	subs = find_matching_substream(chip, stream, target->sync_ep,
 				       target->fmt_type);
 	if (!subs)
 		return sync_fmt;

 	high_score = 0;
 	list_for_each_entry(fp, &subs->fmt_list, list) {
 		score = match_endpoint_audioformats(subs, fp,
 						    params_rate(params),
 						    params_channels(params),
 						    params_format(params));
 		if (score > high_score) {
 			sync_fmt = fp;
 			high_score = score;
 		}
 	}

 	return sync_fmt;
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	//
	// Special handling for implicit feedback mode
	//

	#include <linux/init.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 <sound/pcm_params.h>

	#include "usbaudio.h"
	#include "card.h"
	#include "helper.h"
	#include "implicit.h"

	enum {
	IMPLICIT_FB_NONE,
	IMPLICIT_FB_GENERIC,
	IMPLICIT_FB_FIXED,
	IMPLICIT_FB_BOTH, /* generic playback + capture (for BOSS) */
	};

	struct snd_usb_implicit_fb_match {
	unsigned int id;
	unsigned int iface_class;
	unsigned int ep_num;
	unsigned int iface;
	int type;
	};

	#define IMPLICIT_FB_GENERIC_DEV(vend, prod) \
	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_GENERIC }
	#define IMPLICIT_FB_FIXED_DEV(vend, prod, ep, ifnum) \
	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_FIXED, .ep_num = (ep),\
	.iface = (ifnum) }
	#define IMPLICIT_FB_BOTH_DEV(vend, prod, ep, ifnum) \
	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_BOTH, .ep_num = (ep),\
	.iface = (ifnum) }
	#define IMPLICIT_FB_SKIP_DEV(vend, prod) \
	{ .id = USB_ID(vend, prod), .type = IMPLICIT_FB_NONE }

	/* Implicit feedback quirk table for playback */
	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(0x0763, 0x2080, 0x81, 2), /* M-Audio FastTrack Ultra */
	IMPLICIT_FB_FIXED_DEV(0x0763, 0x2081, 0x81, 2), /* M-Audio FastTrack Ultra */
	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+ */
	IMPLICIT_FB_FIXED_DEV(0x0499, 0x172f, 0x81, 2), /* Steinberg UR22C */
	IMPLICIT_FB_FIXED_DEV(0x0d9a, 0x00df, 0x81, 2), /* RTX6001 */
	IMPLICIT_FB_FIXED_DEV(0x22f0, 0x0006, 0x81, 3), /* Allen&Heath Qu-16 */
	IMPLICIT_FB_FIXED_DEV(0x1686, 0xf029, 0x82, 2), /* Zoom UAC-2 */
	IMPLICIT_FB_FIXED_DEV(0x2466, 0x8003, 0x86, 2), /* Fractal Audio Axe-Fx II */
	IMPLICIT_FB_FIXED_DEV(0x0499, 0x172a, 0x86, 2), /* Yamaha MODX */

	/* Special matching */
	{ .id = USB_ID(0x07fd, 0x0004), .iface_class = USB_CLASS_AUDIO,
	.type = IMPLICIT_FB_NONE }, /* MicroBook IIc */
	/* ep = 0x84, ifnum = 0 */
	{ .id = USB_ID(0x07fd, 0x0004), .iface_class = USB_CLASS_VENDOR_SPEC,
	.type = IMPLICIT_FB_FIXED,
	.ep_num = 0x84, .iface = 0 }, /* MOTU MicroBook II */

	{} /* terminator */
	};

	/* Implicit feedback quirk table for capture: only FIXED type */
	static const struct snd_usb_implicit_fb_match capture_implicit_fb_quirks[] = {
	{} /* terminator */
	};

	/* set up sync EP information on the audioformat */
	static int add_implicit_fb_sync_ep(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	int ep, int ep_idx, int ifnum,
	const struct usb_host_interface *alts)
	{
	struct usb_interface *iface;

	if (!alts) {
	iface = usb_ifnum_to_if(chip->dev, ifnum);
	if (!iface \|\| iface->num_altsetting < 2)
	return 0;
	alts = &iface->altsetting[1];
	}

	fmt->sync_ep = ep;
	fmt->sync_iface = ifnum;
	fmt->sync_altsetting = alts->desc.bAlternateSetting;
	fmt->sync_ep_idx = ep_idx;
	fmt->implicit_fb = 1;
	usb_audio_dbg(chip,
	"%d:%d: added %s implicit_fb sync_ep %x, iface %d:%d\n",
	fmt->iface, fmt->altsetting,
	(ep & USB_DIR_IN) ? "playback" : "capture",
	fmt->sync_ep, fmt->sync_iface, fmt->sync_altsetting);
	return 1;
	}

	/* Check whether the given UAC2 iface:altset points to an implicit fb source */
	static int add_generic_uac2_implicit_fb(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	unsigned int ifnum,
	unsigned int altsetting)
	{
	struct usb_host_interface *alts;
	struct usb_endpoint_descriptor *epd;

	alts = snd_usb_get_host_interface(chip, ifnum, altsetting);
	if (!alts)
	return 0;
	if (alts->desc.bInterfaceClass != USB_CLASS_AUDIO \|\|
	alts->desc.bInterfaceSubClass != USB_SUBCLASS_AUDIOSTREAMING \|\|
	alts->desc.bInterfaceProtocol != UAC_VERSION_2 \|\|
	alts->desc.bNumEndpoints < 1)
	return 0;
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_in(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
	USB_ENDPOINT_USAGE_IMPLICIT_FB)
	return 0;
	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
	ifnum, alts);
	}

	static bool roland_sanity_check_iface(struct usb_host_interface *alts)
	{
	if (alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC \|\|
	(alts->desc.bInterfaceSubClass != 2 &&
	alts->desc.bInterfaceProtocol != 2) \|\|
	alts->desc.bNumEndpoints < 1)
	return false;
	return true;
	}

	/* Like the UAC2 case above, but specific to Roland with vendor class and hack */
	static int add_roland_implicit_fb(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	struct usb_endpoint_descriptor *epd;

	if (!roland_sanity_check_iface(alts))
	return 0;
	/* only when both streams are with ASYNC type */
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_out(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return 0;

	/* check capture EP */
	alts = snd_usb_get_host_interface(chip,
	alts->desc.bInterfaceNumber + 1,
	alts->desc.bAlternateSetting);
	if (!alts \|\| !roland_sanity_check_iface(alts))
	return 0;
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_in(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return 0;
	chip->quirk_flags \|= QUIRK_FLAG_PLAYBACK_FIRST;
	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
	alts->desc.bInterfaceNumber, alts);
	}

	/* capture quirk for Roland device; always full-duplex */
	static int add_roland_capture_quirk(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	struct usb_endpoint_descriptor *epd;

	if (!roland_sanity_check_iface(alts))
	return 0;
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_in(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return 0;

	alts = snd_usb_get_host_interface(chip,
	alts->desc.bInterfaceNumber - 1,
	alts->desc.bAlternateSetting);
	if (!alts \|\| !roland_sanity_check_iface(alts))
	return 0;
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_out(epd))
	return 0;
	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
	alts->desc.bInterfaceNumber, alts);
	}

	/* Playback and capture EPs on Pioneer devices share the same iface/altset
	* for the implicit feedback operation
	*/
	static bool is_pioneer_implicit_fb(struct snd_usb_audio *chip,
	struct usb_host_interface *alts)

	{
	struct usb_endpoint_descriptor *epd;

	if (USB_ID_VENDOR(chip->usb_id) != 0x2b73 &&
	USB_ID_VENDOR(chip->usb_id) != 0x08e4)
	return false;
	if (alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC)
	return false;
	if (alts->desc.bNumEndpoints != 2)
	return false;

	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_out(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return false;

	epd = get_endpoint(alts, 1);
	if (!usb_endpoint_is_isoc_in(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC \|\|
	((epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
	USB_ENDPOINT_USAGE_DATA &&
	(epd->bmAttributes & USB_ENDPOINT_USAGE_MASK) !=
	USB_ENDPOINT_USAGE_IMPLICIT_FB))
	return false;

	return true;
	}

	static int __add_generic_implicit_fb(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	int iface, int altset)
	{
	struct usb_host_interface *alts;
	struct usb_endpoint_descriptor *epd;

	alts = snd_usb_get_host_interface(chip, iface, altset);
	if (!alts)
	return 0;

	if ((alts->desc.bInterfaceClass != USB_CLASS_VENDOR_SPEC &&
	alts->desc.bInterfaceClass != USB_CLASS_AUDIO) \|\|
	alts->desc.bNumEndpoints < 1)
	return 0;
	epd = get_endpoint(alts, 0);
	if (!usb_endpoint_is_isoc_in(epd) \|\|
	(epd->bmAttributes & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return 0;
	return add_implicit_fb_sync_ep(chip, fmt, epd->bEndpointAddress, 0,
	iface, alts);
	}

	/* More generic quirk: look for the sync EP next to the data EP */
	static int add_generic_implicit_fb(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	if ((fmt->ep_attr & USB_ENDPOINT_SYNCTYPE) != USB_ENDPOINT_SYNC_ASYNC)
	return 0;

	if (__add_generic_implicit_fb(chip, fmt,
	alts->desc.bInterfaceNumber + 1,
	alts->desc.bAlternateSetting))
	return 1;
	return __add_generic_implicit_fb(chip, fmt,
	alts->desc.bInterfaceNumber - 1,
	alts->desc.bAlternateSetting);
	}

	static const struct snd_usb_implicit_fb_match *
	find_implicit_fb_entry(struct snd_usb_audio *chip,
	const struct snd_usb_implicit_fb_match *match,
	const struct usb_host_interface *alts)
	{
	for (; match->id; match++)
	if (match->id == chip->usb_id &&
	(!match->iface_class \|\|
	(alts->desc.bInterfaceClass == match->iface_class)))
	return match;

	return NULL;
	}

	/* Setup an implicit feedback endpoint from a quirk. Returns 0 if no quirk
	* applies. Returns 1 if a quirk was found.
	*/
	static int audioformat_implicit_fb_quirk(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	const struct snd_usb_implicit_fb_match *p;
	unsigned int attr = fmt->ep_attr & USB_ENDPOINT_SYNCTYPE;

	p = find_implicit_fb_entry(chip, playback_implicit_fb_quirks, alts);
	if (p) {
	switch (p->type) {
	case IMPLICIT_FB_GENERIC:
	return add_generic_implicit_fb(chip, fmt, alts);
	case IMPLICIT_FB_NONE:
	return 0; /* No quirk */
	case IMPLICIT_FB_FIXED:
	return add_implicit_fb_sync_ep(chip, fmt, p->ep_num, 0,
	p->iface, NULL);
	}
	}

	/* Special handling for devices with capture quirks */
	p = find_implicit_fb_entry(chip, capture_implicit_fb_quirks, alts);
	if (p) {
	switch (p->type) {
	case IMPLICIT_FB_FIXED:
	return 0; /* no quirk */
	case IMPLICIT_FB_BOTH:
	chip->quirk_flags \|= QUIRK_FLAG_PLAYBACK_FIRST;
	return add_generic_implicit_fb(chip, fmt, alts);
	}
	}

	/* Generic UAC2 implicit feedback */
	if (attr == USB_ENDPOINT_SYNC_ASYNC &&
	alts->desc.bInterfaceClass == USB_CLASS_AUDIO &&
	alts->desc.bInterfaceProtocol == UAC_VERSION_2 &&
	alts->desc.bNumEndpoints == 1) {
	if (add_generic_uac2_implicit_fb(chip, fmt,
	alts->desc.bInterfaceNumber + 1,
	alts->desc.bAlternateSetting))
	return 1;
	}

	/* Roland/BOSS implicit feedback with vendor spec class */
	if (USB_ID_VENDOR(chip->usb_id) == 0x0582) {
	if (add_roland_implicit_fb(chip, fmt, alts) > 0)
	return 1;
	}

	/* Pioneer devices with vendor spec class */
	if (is_pioneer_implicit_fb(chip, alts)) {
	chip->quirk_flags \|= QUIRK_FLAG_PLAYBACK_FIRST;
	return add_implicit_fb_sync_ep(chip, fmt,
	get_endpoint(alts, 1)->bEndpointAddress,
	1, alts->desc.bInterfaceNumber,
	alts);
	}

	/* Try the generic implicit fb if available */
	if (chip->generic_implicit_fb \|\|
	(chip->quirk_flags & QUIRK_FLAG_GENERIC_IMPLICIT_FB))
	return add_generic_implicit_fb(chip, fmt, alts);

	/* No quirk */
	return 0;
	}

	/* same for capture, but only handling FIXED entry */
	static int audioformat_capture_quirk(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	const struct snd_usb_implicit_fb_match *p;

	p = find_implicit_fb_entry(chip, capture_implicit_fb_quirks, alts);
	if (p && (p->type == IMPLICIT_FB_FIXED \|\| p->type == IMPLICIT_FB_BOTH))
	return add_implicit_fb_sync_ep(chip, fmt, p->ep_num, 0,
	p->iface, NULL);

	/* Roland/BOSS need full-duplex streams */
	if (USB_ID_VENDOR(chip->usb_id) == 0x0582) {
	if (add_roland_capture_quirk(chip, fmt, alts) > 0)
	return 1;
	}

	if (is_pioneer_implicit_fb(chip, alts))
	return 1; /* skip the quirk, also don't handle generic sync EP */
	return 0;
	}

	/*
	* Parse altset and set up implicit feedback endpoint on the audioformat
	*/
	int snd_usb_parse_implicit_fb_quirk(struct snd_usb_audio *chip,
	struct audioformat *fmt,
	struct usb_host_interface *alts)
	{
	if (chip->quirk_flags & QUIRK_FLAG_SKIP_IMPLICIT_FB)
	return 0;
	if (fmt->endpoint & USB_DIR_IN)
	return audioformat_capture_quirk(chip, fmt, alts);
	else
	return audioformat_implicit_fb_quirk(chip, fmt, alts);
	}

	/*
	* Return the score of matching two audioformats.
	* Veto the audioformat if:
	* - It has no channels for some reason.
	* - Requested PCM format is not supported.
	* - Requested sample rate is not supported.
	*/
	static int match_endpoint_audioformats(struct snd_usb_substream *subs,
	const struct audioformat *fp,
	int rate, int channels,
	snd_pcm_format_t pcm_format)
	{
	int i, score;

	if (fp->channels < 1)
	return 0;

	if (!(fp->formats & pcm_format_to_bits(pcm_format)))
	return 0;

	if (fp->rates & SNDRV_PCM_RATE_CONTINUOUS) {
	if (rate < fp->rate_min \|\| rate > fp->rate_max)
	return 0;
	} else {
	for (i = 0; i < fp->nr_rates; i++) {
	if (fp->rate_table[i] == rate)
	break;
	}
	if (i >= fp->nr_rates)
	return 0;
	}

	score = 1;
	if (fp->channels == channels)
	score++;

	return score;
	}

	static struct snd_usb_substream *
	find_matching_substream(struct snd_usb_audio *chip, int stream, int ep_num,
	int fmt_type)
	{
	struct snd_usb_stream *as;
	struct snd_usb_substream *subs;

	list_for_each_entry(as, &chip->pcm_list, list) {
	subs = &as->substream[stream];
	if (as->fmt_type == fmt_type && subs->ep_num == ep_num)
	return subs;
	}

	return NULL;
	}

	/*
	* Return the audioformat that is suitable for the implicit fb
	*/
	const struct audioformat *
	snd_usb_find_implicit_fb_sync_format(struct snd_usb_audio *chip,
	const struct audioformat *target,
	const struct snd_pcm_hw_params *params,
	int stream)
	{
	struct snd_usb_substream *subs;
	const struct audioformat fp, sync_fmt = NULL;
	int score, high_score;

	/* Use the original audioformat as fallback for the shared altset */
	if (target->iface == target->sync_iface &&
	target->altsetting == target->sync_altsetting)
	sync_fmt = target;

	subs = find_matching_substream(chip, stream, target->sync_ep,
	target->fmt_type);
	if (!subs)
	return sync_fmt;

	high_score = 0;
	list_for_each_entry(fp, &subs->fmt_list, list) {
	score = match_endpoint_audioformats(subs, fp,
	params_rate(params),
	params_channels(params),
	params_format(params));
	if (score > high_score) {
	sync_fmt = fp;
	high_score = score;
	}
	}

	return sync_fmt;
	}