usb: gadget: f_uac2: split out audio core

Abstract the peripheral side ALSA sound card code from
the f_uac2 function into a component that can be called
by various functions, so the various flavors can be split
apart and selectively reused.

Visible changes:
- add uac_params structure to pass audio paramteres for
g_audio_setup
- make ALSA sound card's name configurable
- add [in/out]_ep_maxpsize
- allocate snd_uac_chip structure during g_audio_setup
- add u_audio_[start/stop]_[capture/playback] functions

Signed-off-by: Ruslan Bilovol <[e-mail]>
Signed-off-by: Felipe Balbi <[e-mail]>

drivers/usb/gadget/Kconfig

···
 config USB_U_ETHER
 	tristate
 
+config USB_U_AUDIO
+	tristate
+
 config USB_F_SERIAL
 	tristate
 
···
 	depends on SND
 	select USB_LIBCOMPOSITE
 	select SND_PCM
+	select USB_U_AUDIO
 	select USB_F_UAC2
 	help
 	  This Audio function is compatible with USB Audio Class

drivers/usb/gadget/function/Makefile

···
 obj-$(CONFIG_USB_F_MASS_STORAGE)+= usb_f_mass_storage.o
 usb_f_fs-y			:= f_fs.o
 obj-$(CONFIG_USB_F_FS)		+= usb_f_fs.o
+obj-$(CONFIG_USB_U_AUDIO)	+= u_audio.o
 usb_f_uac1-y			:= f_uac1.o u_uac1.o
 obj-$(CONFIG_USB_F_UAC1)	+= usb_f_uac1.o
 usb_f_uac2-y			:= f_uac2.o

drivers/usb/gadget/function/f_uac2.c

···
 #include <linux/usb/audio-v2.h>
 #include <linux/module.h>
 
-#include <sound/core.h>
-#include <sound/pcm.h>
-#include <sound/pcm_params.h>
-
+#include "u_audio.h"
 #include "u_uac2.h"
 
 /*
···
 #define UNFLW_CTRL	8
 #define OVFLW_CTRL	10
 
-struct uac2_req {
-	struct uac2_rtd_params *pp; /* parent param */
-	struct usb_request *req;
+struct f_uac2 {
+	struct g_audio g_audio;
+	u8 ac_intf, as_in_intf, as_out_intf;
+	u8 ac_alt, as_in_alt, as_out_alt;	/* needed for get_alt() */
 };
 
-struct uac2_rtd_params {
-	struct snd_uac2_chip *uac2; /* parent chip */
-	bool ep_enabled; /* if the ep is enabled */
-	/* Size of the ring buffer */
-	size_t dma_bytes;
-	unsigned char *dma_area;
-
-	struct snd_pcm_substream *ss;
-
-	/* Ring buffer */
-	ssize_t hw_ptr;
-
-	void *rbuf;
-
-	size_t period_size;
-
-	unsigned max_psize;
-	struct uac2_req *ureq;
-
-	spinlock_t lock;
-};
-
-struct snd_uac2_chip {
-	struct uac2_rtd_params p_prm;
-	struct uac2_rtd_params c_prm;
-
-	struct snd_card *card;
-	struct snd_pcm *pcm;
-
-	/* timekeeping for the playback endpoint */
-	unsigned int p_interval;
-	unsigned int p_residue;
-
-	/* pre-calculated values for playback iso completion */
-	unsigned int p_pktsize;
-	unsigned int p_pktsize_residue;
-	unsigned int p_framesize;
-};
-
-#define BUFF_SIZE_MAX	(PAGE_SIZE * 16)
-#define PRD_SIZE_MAX	PAGE_SIZE
-#define MIN_PERIODS	4
-
-static struct snd_pcm_hardware uac2_pcm_hardware = {
-	.info = SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER
-		 | SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID
-		 | SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME,
-	.rates = SNDRV_PCM_RATE_CONTINUOUS,
-	.periods_max = BUFF_SIZE_MAX / PRD_SIZE_MAX,
-	.buffer_bytes_max = BUFF_SIZE_MAX,
-	.period_bytes_max = PRD_SIZE_MAX,
-	.periods_min = MIN_PERIODS,
-};
-
-struct audio_dev {
-	u8 ac_intf, ac_alt;
-	u8 as_out_intf, as_out_alt;
-	u8 as_in_intf, as_in_alt;
-
-	struct usb_ep *in_ep, *out_ep;
-	struct usb_function func;
-	struct usb_gadget *gadget;
-
-	/* The ALSA Sound Card it represents on the USB-Client side */
-	struct snd_uac2_chip uac2;
-};
-
-static inline
-struct audio_dev *func_to_agdev(struct usb_function *f)
+static inline struct f_uac2 *func_to_uac2(struct usb_function *f)
 {
-	return container_of(f, struct audio_dev, func);
+	return container_of(f, struct f_uac2, g_audio.func);
 }
 
 static inline
-struct audio_dev *uac2_to_agdev(struct snd_uac2_chip *u)
-{
-	return container_of(u, struct audio_dev, uac2);
-}
-
-static inline
-struct f_uac2_opts *agdev_to_uac2_opts(struct audio_dev *agdev)
+struct f_uac2_opts *g_audio_to_uac2_opts(struct g_audio *agdev)
 {
 	return container_of(agdev->func.fi, struct f_uac2_opts, func_inst);
 }
-
-static inline
-uint num_channels(uint chanmask)
-{
-	uint num = 0;
-
-	while (chanmask) {
-		num += (chanmask & 1);
-		chanmask >>= 1;
-	}
-
-	return num;
-}
-
-static void
-agdev_iso_complete(struct usb_ep *ep, struct usb_request *req)
-{
-	unsigned pending;
-	unsigned long flags;
-	unsigned int hw_ptr;
-	bool update_alsa = false;
-	int status = req->status;
-	struct uac2_req *ur = req->context;
-	struct snd_pcm_substream *substream;
-	struct uac2_rtd_params *prm = ur->pp;
-	struct snd_uac2_chip *uac2 = prm->uac2;
-
-	/* i/f shutting down */
-	if (!prm->ep_enabled || req->status == -ESHUTDOWN)
-		return;
-
-	/*
-	 * We can't really do much about bad xfers.
-	 * Afterall, the ISOCH xfers could fail legitimately.
-	 */
-	if (status)
-		pr_debug("%s: iso_complete status(%d) %d/%d\n",
-			__func__, status, req->actual, req->length);
-
-	substream = prm->ss;
-
-	/* Do nothing if ALSA isn't active */
-	if (!substream)
-		goto exit;
-
-	spin_lock_irqsave(&prm->lock, flags);
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-		/*
-		 * For each IN packet, take the quotient of the current data
-		 * rate and the endpoint's interval as the base packet size.
-		 * If there is a residue from this division, add it to the
-		 * residue accumulator.
-		 */
-		req->length = uac2->p_pktsize;
-		uac2->p_residue += uac2->p_pktsize_residue;
-
-		/*
-		 * Whenever there are more bytes in the accumulator than we
-		 * need to add one more sample frame, increase this packet's
-		 * size and decrease the accumulator.
-		 */
-		if (uac2->p_residue / uac2->p_interval >= uac2->p_framesize) {
-			req->length += uac2->p_framesize;
-			uac2->p_residue -= uac2->p_framesize *
-					   uac2->p_interval;
-		}
-
-		req->actual = req->length;
-	}
-
-	pending = prm->hw_ptr % prm->period_size;
-	pending += req->actual;
-	if (pending >= prm->period_size)
-		update_alsa = true;
-
-	hw_ptr = prm->hw_ptr;
-	prm->hw_ptr = (prm->hw_ptr + req->actual) % prm->dma_bytes;
-
-	spin_unlock_irqrestore(&prm->lock, flags);
-
-	/* Pack USB load in ALSA ring buffer */
-	pending = prm->dma_bytes - hw_ptr;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-		if (unlikely(pending < req->actual)) {
-			memcpy(req->buf, prm->dma_area + hw_ptr, pending);
-			memcpy(req->buf + pending, prm->dma_area,
-			       req->actual - pending);
-		} else {
-			memcpy(req->buf, prm->dma_area + hw_ptr, req->actual);
-		}
-	} else {
-		if (unlikely(pending < req->actual)) {
-			memcpy(prm->dma_area + hw_ptr, req->buf, pending);
-			memcpy(prm->dma_area, req->buf + pending,
-			       req->actual - pending);
-		} else {
-			memcpy(prm->dma_area + hw_ptr, req->buf, req->actual);
-		}
-	}
-
-exit:
-	if (usb_ep_queue(ep, req, GFP_ATOMIC))
-		dev_err(uac2->card->dev, "%d Error!\n", __LINE__);
-
-	if (update_alsa)
-		snd_pcm_period_elapsed(substream);
-
-	return;
-}
-
-static int
-uac2_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
-{
-	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
-	struct audio_dev *agdev = uac2_to_agdev(uac2);
-	struct f_uac2_opts *uac2_opts = agdev_to_uac2_opts(agdev);
-	struct uac2_rtd_params *prm;
-	unsigned long flags;
-	int err = 0;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-		prm = &uac2->p_prm;
-	else
-		prm = &uac2->c_prm;
-
-	spin_lock_irqsave(&prm->lock, flags);
-
-	/* Reset */
-	prm->hw_ptr = 0;
-
-	switch (cmd) {
-	case SNDRV_PCM_TRIGGER_START:
-	case SNDRV_PCM_TRIGGER_RESUME:
-		prm->ss = substream;
-		break;
-	case SNDRV_PCM_TRIGGER_STOP:
-	case SNDRV_PCM_TRIGGER_SUSPEND:
-		prm->ss = NULL;
-		break;
-	default:
-		err = -EINVAL;
-	}
-
-	spin_unlock_irqrestore(&prm->lock, flags);
-
-	/* Clear buffer after Play stops */
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && !prm->ss)
-		memset(prm->rbuf, 0, prm->max_psize * uac2_opts->req_number);
-
-	return err;
-}
-
-static snd_pcm_uframes_t uac2_pcm_pointer(struct snd_pcm_substream *substream)
-{
-	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
-	struct uac2_rtd_params *prm;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-		prm = &uac2->p_prm;
-	else
-		prm = &uac2->c_prm;
-
-	return bytes_to_frames(substream->runtime, prm->hw_ptr);
-}
-
-static int uac2_pcm_hw_params(struct snd_pcm_substream *substream,
-			       struct snd_pcm_hw_params *hw_params)
-{
-	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
-	struct uac2_rtd_params *prm;
-	int err;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-		prm = &uac2->p_prm;
-	else
-		prm = &uac2->c_prm;
-
-	err = snd_pcm_lib_malloc_pages(substream,
-					params_buffer_bytes(hw_params));
-	if (err >= 0) {
-		prm->dma_bytes = substream->runtime->dma_bytes;
-		prm->dma_area = substream->runtime->dma_area;
-		prm->period_size = params_period_bytes(hw_params);
-	}
-
-	return err;
-}
-
-static int uac2_pcm_hw_free(struct snd_pcm_substream *substream)
-{
-	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
-	struct uac2_rtd_params *prm;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
-		prm = &uac2->p_prm;
-	else
-		prm = &uac2->c_prm;
-
-	prm->dma_area = NULL;
-	prm->dma_bytes = 0;
-	prm->period_size = 0;
-
-	return snd_pcm_lib_free_pages(substream);
-}
-
-static int uac2_pcm_open(struct snd_pcm_substream *substream)
-{
-	struct snd_uac2_chip *uac2 = snd_pcm_substream_chip(substream);
-	struct snd_pcm_runtime *runtime = substream->runtime;
-	struct audio_dev *audio_dev;
-	struct f_uac2_opts *opts;
-	int p_ssize, c_ssize;
-	int p_srate, c_srate;
-	int p_chmask, c_chmask;
-
-	audio_dev = uac2_to_agdev(uac2);
-	opts = container_of(audio_dev->func.fi, struct f_uac2_opts, func_inst);
-	p_ssize = opts->p_ssize;
-	c_ssize = opts->c_ssize;
-	p_srate = opts->p_srate;
-	c_srate = opts->c_srate;
-	p_chmask = opts->p_chmask;
-	c_chmask = opts->c_chmask;
-	uac2->p_residue = 0;
-
-	runtime->hw = uac2_pcm_hardware;
-
-	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
-		spin_lock_init(&uac2->p_prm.lock);
-		runtime->hw.rate_min = p_srate;
-		switch (p_ssize) {
-		case 3:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
-			break;
-		case 4:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
-			break;
-		default:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
-			break;
-		}
-		runtime->hw.channels_min = num_channels(p_chmask);
-		runtime->hw.period_bytes_min = 2 * uac2->p_prm.max_psize
-						/ runtime->hw.periods_min;
-	} else {
-		spin_lock_init(&uac2->c_prm.lock);
-		runtime->hw.rate_min = c_srate;
-		switch (c_ssize) {
-		case 3:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
-			break;
-		case 4:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
-			break;
-		default:
-			runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
-			break;
-		}
-		runtime->hw.channels_min = num_channels(c_chmask);
-		runtime->hw.period_bytes_min = 2 * uac2->c_prm.max_psize
-						/ runtime->hw.periods_min;
-	}
-
-	runtime->hw.rate_max = runtime->hw.rate_min;
-	runtime->hw.channels_max = runtime->hw.channels_min;
-
-	snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
-
-	return 0;
-}
-
-/* ALSA cries without these function pointers */
-static int uac2_pcm_null(struct snd_pcm_substream *substream)
-{
-	return 0;
-}
-
-static struct snd_pcm_ops uac2_pcm_ops = {
-	.open = uac2_pcm_open,
-	.close = uac2_pcm_null,
-	.ioctl = snd_pcm_lib_ioctl,
-	.hw_params = uac2_pcm_hw_params,
-	.hw_free = uac2_pcm_hw_free,
-	.trigger = uac2_pcm_trigger,
-	.pointer = uac2_pcm_pointer,
-	.prepare = uac2_pcm_null,
-};
-
-static int snd_uac2_probe(struct audio_dev *audio_dev)
-{
-	struct snd_uac2_chip *uac2 = &audio_dev->uac2;
-	struct snd_card *card;
-	struct snd_pcm *pcm;
-	struct f_uac2_opts *opts;
-	int err;
-	int p_chmask, c_chmask;
-
-	opts = container_of(audio_dev->func.fi, struct f_uac2_opts, func_inst);
-	p_chmask = opts->p_chmask;
-	c_chmask = opts->c_chmask;
-
-	/* Choose any slot, with no id */
-	err = snd_card_new(&audio_dev->gadget->dev,
-			-1, NULL, THIS_MODULE, 0, &card);
-	if (err < 0)
-		return err;
-
-	uac2->card = card;
-
-	/*
-	 * Create first PCM device
-	 * Create a substream only for non-zero channel streams
-	 */
-	err = snd_pcm_new(uac2->card, "UAC2 PCM", 0,
-			       p_chmask ? 1 : 0, c_chmask ? 1 : 0, &pcm);
-	if (err < 0)
-		goto snd_fail;
-
-	strcpy(pcm->name, "UAC2 PCM");
-	pcm->private_data = uac2;
-
-	uac2->pcm = pcm;
-
-	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &uac2_pcm_ops);
-	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &uac2_pcm_ops);
-
-	strcpy(card->driver, "UAC2_Gadget");
-	strcpy(card->shortname, "UAC2_Gadget");
-	sprintf(card->longname, "UAC2_Gadget %i", card->dev->id);
-
-	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
-		snd_dma_continuous_data(GFP_KERNEL), 0, BUFF_SIZE_MAX);
-
-	err = snd_card_register(card);
-
-	if (!err)
-		return 0;
-
-snd_fail:
-	snd_card_free(card);
-
-	uac2->pcm = NULL;
-	uac2->card = NULL;
-
-	return err;
-}
-
-static int snd_uac2_remove(struct audio_dev *audio_dev)
-{
-	struct snd_card *card = audio_dev->uac2.card;
-
-	if (card)
-		return snd_card_free(card);
-
-	return 0;
-}
-
 
 /* --------- USB Function Interface ------------- */
 
···
 	__u32	dRES;
 } __packed;
 
-static inline void
-free_ep(struct uac2_rtd_params *prm, struct usb_ep *ep)
-{
-	struct snd_uac2_chip *uac2 = prm->uac2;
-	struct audio_dev *agdev = uac2_to_agdev(uac2);
-	struct f_uac2_opts *uac2_opts = agdev_to_uac2_opts(agdev);
-	int i;
-
-	if (!prm->ep_enabled)
-		return;
-
-	prm->ep_enabled = false;
-
-	for (i = 0; i < uac2_opts->req_number; i++) {
-		if (prm->ureq[i].req) {
-			usb_ep_dequeue(ep, prm->ureq[i].req);
-			usb_ep_free_request(ep, prm->ureq[i].req);
-			prm->ureq[i].req = NULL;
-		}
-	}
-
-	if (usb_ep_disable(ep))
-		dev_err(uac2->card->dev,
-			"%s:%d Error!\n", __func__, __LINE__);
-}
-
 static void set_ep_max_packet_size(const struct f_uac2_opts *uac2_opts,
 	struct usb_endpoint_descriptor *ep_desc,
 	unsigned int factor, bool is_playback)
···
 static int
 afunc_bind(struct usb_configuration *cfg, struct usb_function *fn)
 {
-	struct audio_dev *agdev = func_to_agdev(fn);
-	struct snd_uac2_chip *uac2 = &agdev->uac2;
+	struct f_uac2 *uac2 = func_to_uac2(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 	struct usb_composite_dev *cdev = cfg->cdev;
 	struct usb_gadget *gadget = cdev->gadget;
 	struct device *dev = &gadget->dev;
-	struct uac2_rtd_params *prm;
 	struct f_uac2_opts *uac2_opts;
 	struct usb_string *us;
 	int ret;
···
 		return ret;
 	}
 	std_ac_if_desc.bInterfaceNumber = ret;
-	agdev->ac_intf = ret;
-	agdev->ac_alt = 0;
+	uac2->ac_intf = ret;
+	uac2->ac_alt = 0;
 
 	ret = usb_interface_id(cfg, fn);
 	if (ret < 0) {
···
 	}
 	std_as_out_if0_desc.bInterfaceNumber = ret;
 	std_as_out_if1_desc.bInterfaceNumber = ret;
-	agdev->as_out_intf = ret;
-	agdev->as_out_alt = 0;
+	uac2->as_out_intf = ret;
+	uac2->as_out_alt = 0;
 
 	ret = usb_interface_id(cfg, fn);
 	if (ret < 0) {
···
 	}
 	std_as_in_if0_desc.bInterfaceNumber = ret;
 	std_as_in_if1_desc.bInterfaceNumber = ret;
-	agdev->as_in_intf = ret;
-	agdev->as_in_alt = 0;
+	uac2->as_in_intf = ret;
+	uac2->as_in_alt = 0;
 
 	/* Calculate wMaxPacketSize according to audio bandwidth */
 	set_ep_max_packet_size(uac2_opts, &fs_epin_desc, 1000, true);
···
 		return ret;
 	}
 
-	uac2->p_prm.uac2 = uac2;
-	uac2->c_prm.uac2 = uac2;
+	agdev->in_ep_maxpsize = max(fs_epin_desc.wMaxPacketSize,
+					hs_epin_desc.wMaxPacketSize);
+	agdev->out_ep_maxpsize = max(fs_epout_desc.wMaxPacketSize,
+					hs_epout_desc.wMaxPacketSize);
 
 	hs_epout_desc.bEndpointAddress = fs_epout_desc.bEndpointAddress;
 	hs_epin_desc.bEndpointAddress = fs_epin_desc.bEndpointAddress;
···
 
 	agdev->gadget = gadget;
 
-	prm = &agdev->uac2.c_prm;
-	prm->max_psize = hs_epout_desc.wMaxPacketSize;
-	prm->ureq = kcalloc(uac2_opts->req_number, sizeof(struct uac2_req),
-			GFP_KERNEL);
-	if (!prm->ureq) {
-		ret = -ENOMEM;
-		goto err_free_descs;
-	}
-	prm->rbuf = kcalloc(uac2_opts->req_number, prm->max_psize, GFP_KERNEL);
-	if (!prm->rbuf) {
-		prm->max_psize = 0;
-		ret = -ENOMEM;
-		goto err_free_descs;
-	}
-
-	prm = &agdev->uac2.p_prm;
-	prm->max_psize = hs_epin_desc.wMaxPacketSize;
-	prm->ureq = kcalloc(uac2_opts->req_number, sizeof(struct uac2_req),
-			GFP_KERNEL);
-	if (!prm->ureq) {
-		ret = -ENOMEM;
-		goto err_free_descs;
-	}
-	prm->rbuf = kcalloc(uac2_opts->req_number, prm->max_psize, GFP_KERNEL);
-	if (!prm->rbuf) {
-		prm->max_psize = 0;
-		ret = -ENOMEM;
-		goto err_no_memory;
-	}
-
-	ret = snd_uac2_probe(agdev);
+	agdev->params.p_chmask = uac2_opts->p_chmask;
+	agdev->params.p_srate = uac2_opts->p_srate;
+	agdev->params.p_ssize = uac2_opts->p_ssize;
+	agdev->params.c_chmask = uac2_opts->c_chmask;
+	agdev->params.c_srate = uac2_opts->c_srate;
+	agdev->params.c_ssize = uac2_opts->c_ssize;
+	agdev->params.req_number = uac2_opts->req_number;
+	ret = g_audio_setup(agdev, "UAC2 PCM", "UAC2_Gadget");
 	if (ret)
-		goto err_no_memory;
+		goto err_free_descs;
 	return 0;
 
-err_no_memory:
-	kfree(agdev->uac2.p_prm.ureq);
-	kfree(agdev->uac2.c_prm.ureq);
-	kfree(agdev->uac2.p_prm.rbuf);
-	kfree(agdev->uac2.c_prm.rbuf);
 err_free_descs:
 	usb_free_all_descriptors(fn);
 	agdev->gadget = NULL;
···
 afunc_set_alt(struct usb_function *fn, unsigned intf, unsigned alt)
 {
 	struct usb_composite_dev *cdev = fn->config->cdev;
-	struct audio_dev *agdev = func_to_agdev(fn);
-	struct f_uac2_opts *opts = agdev_to_uac2_opts(agdev);
-	struct snd_uac2_chip *uac2 = &agdev->uac2;
+	struct f_uac2 *uac2 = func_to_uac2(fn);
 	struct usb_gadget *gadget = cdev->gadget;
 	struct device *dev = &gadget->dev;
-	struct usb_request *req;
-	struct usb_ep *ep;
-	struct uac2_rtd_params *prm;
-	int req_len, i;
+	int ret = 0;
 
 	/* No i/f has more than 2 alt settings */
 	if (alt > 1) {
···
 		return -EINVAL;
 	}
 
-	if (intf == agdev->ac_intf) {
+	if (intf == uac2->ac_intf) {
 		/* Control I/f has only 1 AltSetting - 0 */
 		if (alt) {
 			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
···
 		return 0;
 	}
 
-	if (intf == agdev->as_out_intf) {
-		ep = agdev->out_ep;
-		prm = &uac2->c_prm;
-		config_ep_by_speed(gadget, fn, ep);
-		agdev->as_out_alt = alt;
-		req_len = prm->max_psize;
-	} else if (intf == agdev->as_in_intf) {
-		unsigned int factor, rate;
-		struct usb_endpoint_descriptor *ep_desc;
+	if (intf == uac2->as_out_intf) {
+		uac2->as_out_alt = alt;
 
-		ep = agdev->in_ep;
-		prm = &uac2->p_prm;
-		config_ep_by_speed(gadget, fn, ep);
-		agdev->as_in_alt = alt;
-
-		/* pre-calculate the playback endpoint's interval */
-		if (gadget->speed == USB_SPEED_FULL) {
-			ep_desc = &fs_epin_desc;
-			factor = 1000;
-		} else {
-			ep_desc = &hs_epin_desc;
-			factor = 8000;
-		}
-
-		/* pre-compute some values for iso_complete() */
-		uac2->p_framesize = opts->p_ssize *
-				    num_channels(opts->p_chmask);
-		rate = opts->p_srate * uac2->p_framesize;
-		uac2->p_interval = factor / (1 << (ep_desc->bInterval - 1));
-		uac2->p_pktsize = min_t(unsigned int, rate / uac2->p_interval,
-					prm->max_psize);
-
-		if (uac2->p_pktsize < prm->max_psize)
-			uac2->p_pktsize_residue = rate % uac2->p_interval;
+		if (alt)
+			ret = u_audio_start_capture(&uac2->g_audio);
 		else
-			uac2->p_pktsize_residue = 0;
+			u_audio_stop_capture(&uac2->g_audio);
+	} else if (intf == uac2->as_in_intf) {
+		uac2->as_in_alt = alt;
 
-		req_len = uac2->p_pktsize;
-		uac2->p_residue = 0;
+		if (alt)
+			ret = u_audio_start_playback(&uac2->g_audio);
+		else
+			u_audio_stop_playback(&uac2->g_audio);
 	} else {
 		dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
 		return -EINVAL;
 	}
 
-	if (alt == 0) {
-		free_ep(prm, ep);
-		return 0;
-	}
-
-	prm->ep_enabled = true;
-	usb_ep_enable(ep);
-
-	for (i = 0; i < opts->req_number; i++) {
-		if (!prm->ureq[i].req) {
-			req = usb_ep_alloc_request(ep, GFP_ATOMIC);
-			if (req == NULL)
-				return -ENOMEM;
-
-			prm->ureq[i].req = req;
-			prm->ureq[i].pp = prm;
-
-			req->zero = 0;
-			req->context = &prm->ureq[i];
-			req->length = req_len;
-			req->complete = agdev_iso_complete;
-			req->buf = prm->rbuf + i * prm->max_psize;
-		}
-
-		if (usb_ep_queue(ep, prm->ureq[i].req, GFP_ATOMIC))
-			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
-	}
-
-	return 0;
+	return ret;
 }
 
 static int
 afunc_get_alt(struct usb_function *fn, unsigned intf)
 {
-	struct audio_dev *agdev = func_to_agdev(fn);
+	struct f_uac2 *uac2 = func_to_uac2(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 
-	if (intf == agdev->ac_intf)
-		return agdev->ac_alt;
-	else if (intf == agdev->as_out_intf)
-		return agdev->as_out_alt;
-	else if (intf == agdev->as_in_intf)
-		return agdev->as_in_alt;
+	if (intf == uac2->ac_intf)
+		return uac2->ac_alt;
+	else if (intf == uac2->as_out_intf)
+		return uac2->as_out_alt;
+	else if (intf == uac2->as_in_intf)
+		return uac2->as_in_alt;
 	else
 		dev_err(&agdev->gadget->dev,
 			"%s:%d Invalid Interface %d!\n",
···
 static void
 afunc_disable(struct usb_function *fn)
 {
-	struct audio_dev *agdev = func_to_agdev(fn);
-	struct snd_uac2_chip *uac2 = &agdev->uac2;
+	struct f_uac2 *uac2 = func_to_uac2(fn);
 
-	free_ep(&uac2->p_prm, agdev->in_ep);
-	agdev->as_in_alt = 0;
-
-	free_ep(&uac2->c_prm, agdev->out_ep);
-	agdev->as_out_alt = 0;
+	uac2->as_in_alt = 0;
+	uac2->as_out_alt = 0;
+	u_audio_stop_capture(&uac2->g_audio);
+	u_audio_stop_playback(&uac2->g_audio);
 }
 
 static int
 in_rq_cur(struct usb_function *fn, const struct usb_ctrlrequest *cr)
 {
 	struct usb_request *req = fn->config->cdev->req;
-	struct audio_dev *agdev = func_to_agdev(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 	struct f_uac2_opts *opts;
 	u16 w_length = le16_to_cpu(cr->wLength);
 	u16 w_index = le16_to_cpu(cr->wIndex);
···
 	int value = -EOPNOTSUPP;
 	int p_srate, c_srate;
 
-	opts = agdev_to_uac2_opts(agdev);
+	opts = g_audio_to_uac2_opts(agdev);
 	p_srate = opts->p_srate;
 	c_srate = opts->c_srate;
 
···
 in_rq_range(struct usb_function *fn, const struct usb_ctrlrequest *cr)
 {
 	struct usb_request *req = fn->config->cdev->req;
-	struct audio_dev *agdev = func_to_agdev(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 	struct f_uac2_opts *opts;
 	u16 w_length = le16_to_cpu(cr->wLength);
 	u16 w_index = le16_to_cpu(cr->wIndex);
···
 	int value = -EOPNOTSUPP;
 	int p_srate, c_srate;
 
-	opts = agdev_to_uac2_opts(agdev);
+	opts = g_audio_to_uac2_opts(agdev);
 	p_srate = opts->p_srate;
 	c_srate = opts->c_srate;
 
···
 static int
 setup_rq_inf(struct usb_function *fn, const struct usb_ctrlrequest *cr)
 {
-	struct audio_dev *agdev = func_to_agdev(fn);
+	struct f_uac2 *uac2 = func_to_uac2(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 	u16 w_index = le16_to_cpu(cr->wIndex);
 	u8 intf = w_index & 0xff;
 
-	if (intf != agdev->ac_intf) {
+	if (intf != uac2->ac_intf) {
 		dev_err(&agdev->gadget->dev,
 			"%s:%d Error!\n", __func__, __LINE__);
 		return -EOPNOTSUPP;
···
 afunc_setup(struct usb_function *fn, const struct usb_ctrlrequest *cr)
 {
 	struct usb_composite_dev *cdev = fn->config->cdev;
-	struct audio_dev *agdev = func_to_agdev(fn);
+	struct g_audio *agdev = func_to_g_audio(fn);
 	struct usb_request *req = cdev->req;
 	u16 w_length = le16_to_cpu(cr->wLength);
 	int value = -EOPNOTSUPP;
···
 
 static void afunc_free(struct usb_function *f)
 {
-	struct audio_dev *agdev;
+	struct g_audio *agdev;
 	struct f_uac2_opts *opts;
 
-	agdev = func_to_agdev(f);
+	agdev = func_to_g_audio(f);
 	opts = container_of(f->fi, struct f_uac2_opts, func_inst);
 	kfree(agdev);
 	mutex_lock(&opts->lock);
···
 
 static void afunc_unbind(struct usb_configuration *c, struct usb_function *f)
 {
-	struct audio_dev *agdev = func_to_agdev(f);
-	struct uac2_rtd_params *prm;
+	struct g_audio *agdev = func_to_g_audio(f);
 
-	snd_uac2_remove(agdev);
-
-	prm = &agdev->uac2.p_prm;
-	kfree(prm->rbuf);
-
-	prm = &agdev->uac2.c_prm;
-	kfree(prm->rbuf);
-	kfree(prm->ureq);
+	g_audio_cleanup(agdev);
 	usb_free_all_descriptors(f);
 
 	agdev->gadget = NULL;
···
 
 static struct usb_function *afunc_alloc(struct usb_function_instance *fi)
 {
-	struct audio_dev *agdev;
+	struct f_uac2	*uac2;
 	struct f_uac2_opts *opts;
 
-	agdev = kzalloc(sizeof(*agdev), GFP_KERNEL);
-	if (agdev == NULL)
+	uac2 = kzalloc(sizeof(*uac2), GFP_KERNEL);
+	if (uac2 == NULL)
 		return ERR_PTR(-ENOMEM);
 
 	opts = container_of(fi, struct f_uac2_opts, func_inst);
···
 	++opts->refcnt;
 	mutex_unlock(&opts->lock);
 
-	agdev->func.name = "uac2_func";
-	agdev->func.bind = afunc_bind;
-	agdev->func.unbind = afunc_unbind;
-	agdev->func.set_alt = afunc_set_alt;
-	agdev->func.get_alt = afunc_get_alt;
-	agdev->func.disable = afunc_disable;
-	agdev->func.setup = afunc_setup;
-	agdev->func.free_func = afunc_free;
+	uac2->g_audio.func.name = "uac2_func";
+	uac2->g_audio.func.bind = afunc_bind;
+	uac2->g_audio.func.unbind = afunc_unbind;
+	uac2->g_audio.func.set_alt = afunc_set_alt;
+	uac2->g_audio.func.get_alt = afunc_get_alt;
+	uac2->g_audio.func.disable = afunc_disable;
+	uac2->g_audio.func.setup = afunc_setup;
+	uac2->g_audio.func.free_func = afunc_free;
 
-	return &agdev->func;
+	return &uac2->g_audio.func;
 }
 
 DECLARE_USB_FUNCTION_INIT(uac2, afunc_alloc_inst, afunc_alloc);

drivers/usb/gadget/function/u_audio.c

···
+/*
+ * u_audio.c -- interface to USB gadget "ALSA sound card" utilities
+ *
+ * Copyright (C) 2016
+ * Author: Ruslan Bilovol <[e-mail]>
+ *
+ * Sound card implementation was cut-and-pasted with changes
+ * from f_uac2.c and has:
+ *    Copyright (C) 2011
+ *    Yadwinder Singh ([e-mail])
+ *    Jaswinder Singh ([e-mail])
+ *
+ * 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.
+ */
+
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/pcm.h>
+#include <sound/pcm_params.h>
+
+#include "u_audio.h"
+
+#define BUFF_SIZE_MAX	(PAGE_SIZE * 16)
+#define PRD_SIZE_MAX	PAGE_SIZE
+#define MIN_PERIODS	4
+
+struct uac_req {
+	struct uac_rtd_params *pp; /* parent param */
+	struct usb_request *req;
+};
+
+/* Runtime data params for one stream */
+struct uac_rtd_params {
+	struct snd_uac_chip *uac; /* parent chip */
+	bool ep_enabled; /* if the ep is enabled */
+	/* Size of the ring buffer */
+	size_t dma_bytes;
+	unsigned char *dma_area;
+
+	struct snd_pcm_substream *ss;
+
+	/* Ring buffer */
+	ssize_t hw_ptr;
+
+	void *rbuf;
+
+	size_t period_size;
+
+	unsigned max_psize;	/* MaxPacketSize of endpoint */
+	struct uac_req *ureq;
+
+	spinlock_t lock;
+};
+
+struct snd_uac_chip {
+	struct g_audio *audio_dev;
+
+	struct uac_rtd_params p_prm;
+	struct uac_rtd_params c_prm;
+
+	struct snd_card *card;
+	struct snd_pcm *pcm;
+
+	/* timekeeping for the playback endpoint */
+	unsigned int p_interval;
+	unsigned int p_residue;
+
+	/* pre-calculated values for playback iso completion */
+	unsigned int p_pktsize;
+	unsigned int p_pktsize_residue;
+	unsigned int p_framesize;
+};
+
+static struct snd_pcm_hardware uac_pcm_hardware = {
+	.info = SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER
+		 | SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID
+		 | SNDRV_PCM_INFO_PAUSE | SNDRV_PCM_INFO_RESUME,
+	.rates = SNDRV_PCM_RATE_CONTINUOUS,
+	.periods_max = BUFF_SIZE_MAX / PRD_SIZE_MAX,
+	.buffer_bytes_max = BUFF_SIZE_MAX,
+	.period_bytes_max = PRD_SIZE_MAX,
+	.periods_min = MIN_PERIODS,
+};
+
+static void u_audio_iso_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	unsigned pending;
+	unsigned long flags;
+	unsigned int hw_ptr;
+	bool update_alsa = false;
+	int status = req->status;
+	struct uac_req *ur = req->context;
+	struct snd_pcm_substream *substream;
+	struct uac_rtd_params *prm = ur->pp;
+	struct snd_uac_chip *uac = prm->uac;
+
+	/* i/f shutting down */
+	if (!prm->ep_enabled || req->status == -ESHUTDOWN)
+		return;
+
+	/*
+	 * We can't really do much about bad xfers.
+	 * Afterall, the ISOCH xfers could fail legitimately.
+	 */
+	if (status)
+		pr_debug("%s: iso_complete status(%d) %d/%d\n",
+			__func__, status, req->actual, req->length);
+
+	substream = prm->ss;
+
+	/* Do nothing if ALSA isn't active */
+	if (!substream)
+		goto exit;
+
+	spin_lock_irqsave(&prm->lock, flags);
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+		/*
+		 * For each IN packet, take the quotient of the current data
+		 * rate and the endpoint's interval as the base packet size.
+		 * If there is a residue from this division, add it to the
+		 * residue accumulator.
+		 */
+		req->length = uac->p_pktsize;
+		uac->p_residue += uac->p_pktsize_residue;
+
+		/*
+		 * Whenever there are more bytes in the accumulator than we
+		 * need to add one more sample frame, increase this packet's
+		 * size and decrease the accumulator.
+		 */
+		if (uac->p_residue / uac->p_interval >= uac->p_framesize) {
+			req->length += uac->p_framesize;
+			uac->p_residue -= uac->p_framesize *
+					   uac->p_interval;
+		}
+
+		req->actual = req->length;
+	}
+
+	pending = prm->hw_ptr % prm->period_size;
+	pending += req->actual;
+	if (pending >= prm->period_size)
+		update_alsa = true;
+
+	hw_ptr = prm->hw_ptr;
+	prm->hw_ptr = (prm->hw_ptr + req->actual) % prm->dma_bytes;
+
+	spin_unlock_irqrestore(&prm->lock, flags);
+
+	/* Pack USB load in ALSA ring buffer */
+	pending = prm->dma_bytes - hw_ptr;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+		if (unlikely(pending < req->actual)) {
+			memcpy(req->buf, prm->dma_area + hw_ptr, pending);
+			memcpy(req->buf + pending, prm->dma_area,
+			       req->actual - pending);
+		} else {
+			memcpy(req->buf, prm->dma_area + hw_ptr, req->actual);
+		}
+	} else {
+		if (unlikely(pending < req->actual)) {
+			memcpy(prm->dma_area + hw_ptr, req->buf, pending);
+			memcpy(prm->dma_area, req->buf + pending,
+			       req->actual - pending);
+		} else {
+			memcpy(prm->dma_area + hw_ptr, req->buf, req->actual);
+		}
+	}
+
+exit:
+	if (usb_ep_queue(ep, req, GFP_ATOMIC))
+		dev_err(uac->card->dev, "%d Error!\n", __LINE__);
+
+	if (update_alsa)
+		snd_pcm_period_elapsed(substream);
+}
+
+static int uac_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
+	struct uac_rtd_params *prm;
+	struct g_audio *audio_dev;
+	struct uac_params *params;
+	unsigned long flags;
+	int err = 0;
+
+	audio_dev = uac->audio_dev;
+	params = &audio_dev->params;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		prm = &uac->p_prm;
+	else
+		prm = &uac->c_prm;
+
+	spin_lock_irqsave(&prm->lock, flags);
+
+	/* Reset */
+	prm->hw_ptr = 0;
+
+	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_START:
+	case SNDRV_PCM_TRIGGER_RESUME:
+		prm->ss = substream;
+		break;
+	case SNDRV_PCM_TRIGGER_STOP:
+	case SNDRV_PCM_TRIGGER_SUSPEND:
+		prm->ss = NULL;
+		break;
+	default:
+		err = -EINVAL;
+	}
+
+	spin_unlock_irqrestore(&prm->lock, flags);
+
+	/* Clear buffer after Play stops */
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK && !prm->ss)
+		memset(prm->rbuf, 0, prm->max_psize * params->req_number);
+
+	return err;
+}
+
+static snd_pcm_uframes_t uac_pcm_pointer(struct snd_pcm_substream *substream)
+{
+	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
+	struct uac_rtd_params *prm;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		prm = &uac->p_prm;
+	else
+		prm = &uac->c_prm;
+
+	return bytes_to_frames(substream->runtime, prm->hw_ptr);
+}
+
+static int uac_pcm_hw_params(struct snd_pcm_substream *substream,
+			       struct snd_pcm_hw_params *hw_params)
+{
+	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
+	struct uac_rtd_params *prm;
+	int err;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		prm = &uac->p_prm;
+	else
+		prm = &uac->c_prm;
+
+	err = snd_pcm_lib_malloc_pages(substream,
+					params_buffer_bytes(hw_params));
+	if (err >= 0) {
+		prm->dma_bytes = substream->runtime->dma_bytes;
+		prm->dma_area = substream->runtime->dma_area;
+		prm->period_size = params_period_bytes(hw_params);
+	}
+
+	return err;
+}
+
+static int uac_pcm_hw_free(struct snd_pcm_substream *substream)
+{
+	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
+	struct uac_rtd_params *prm;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		prm = &uac->p_prm;
+	else
+		prm = &uac->c_prm;
+
+	prm->dma_area = NULL;
+	prm->dma_bytes = 0;
+	prm->period_size = 0;
+
+	return snd_pcm_lib_free_pages(substream);
+}
+
+static int uac_pcm_open(struct snd_pcm_substream *substream)
+{
+	struct snd_uac_chip *uac = snd_pcm_substream_chip(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct g_audio *audio_dev;
+	struct uac_params *params;
+	int p_ssize, c_ssize;
+	int p_srate, c_srate;
+	int p_chmask, c_chmask;
+
+	audio_dev = uac->audio_dev;
+	params = &audio_dev->params;
+	p_ssize = params->p_ssize;
+	c_ssize = params->c_ssize;
+	p_srate = params->p_srate;
+	c_srate = params->c_srate;
+	p_chmask = params->p_chmask;
+	c_chmask = params->c_chmask;
+	uac->p_residue = 0;
+
+	runtime->hw = uac_pcm_hardware;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
+		spin_lock_init(&uac->p_prm.lock);
+		runtime->hw.rate_min = p_srate;
+		switch (p_ssize) {
+		case 3:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
+			break;
+		case 4:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
+			break;
+		default:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
+			break;
+		}
+		runtime->hw.channels_min = num_channels(p_chmask);
+		runtime->hw.period_bytes_min = 2 * uac->p_prm.max_psize
+						/ runtime->hw.periods_min;
+	} else {
+		spin_lock_init(&uac->c_prm.lock);
+		runtime->hw.rate_min = c_srate;
+		switch (c_ssize) {
+		case 3:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S24_3LE;
+			break;
+		case 4:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S32_LE;
+			break;
+		default:
+			runtime->hw.formats = SNDRV_PCM_FMTBIT_S16_LE;
+			break;
+		}
+		runtime->hw.channels_min = num_channels(c_chmask);
+		runtime->hw.period_bytes_min = 2 * uac->c_prm.max_psize
+						/ runtime->hw.periods_min;
+	}
+
+	runtime->hw.rate_max = runtime->hw.rate_min;
+	runtime->hw.channels_max = runtime->hw.channels_min;
+
+	snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
+
+	return 0;
+}
+
+/* ALSA cries without these function pointers */
+static int uac_pcm_null(struct snd_pcm_substream *substream)
+{
+	return 0;
+}
+
+static struct snd_pcm_ops uac_pcm_ops = {
+	.open = uac_pcm_open,
+	.close = uac_pcm_null,
+	.ioctl = snd_pcm_lib_ioctl,
+	.hw_params = uac_pcm_hw_params,
+	.hw_free = uac_pcm_hw_free,
+	.trigger = uac_pcm_trigger,
+	.pointer = uac_pcm_pointer,
+	.prepare = uac_pcm_null,
+};
+
+static inline void free_ep(struct uac_rtd_params *prm, struct usb_ep *ep)
+{
+	struct snd_uac_chip *uac = prm->uac;
+	struct g_audio *audio_dev;
+	struct uac_params *params;
+	int i;
+
+	if (!prm->ep_enabled)
+		return;
+
+	prm->ep_enabled = false;
+
+	audio_dev = uac->audio_dev;
+	params = &audio_dev->params;
+
+	for (i = 0; i < params->req_number; i++) {
+		if (prm->ureq[i].req) {
+			usb_ep_dequeue(ep, prm->ureq[i].req);
+			usb_ep_free_request(ep, prm->ureq[i].req);
+			prm->ureq[i].req = NULL;
+		}
+	}
+
+	if (usb_ep_disable(ep))
+		dev_err(uac->card->dev, "%s:%d Error!\n", __func__, __LINE__);
+}
+
+
+int u_audio_start_capture(struct g_audio *audio_dev)
+{
+	struct snd_uac_chip *uac = audio_dev->uac;
+	struct usb_gadget *gadget = audio_dev->gadget;
+	struct device *dev = &gadget->dev;
+	struct usb_request *req;
+	struct usb_ep *ep;
+	struct uac_rtd_params *prm;
+	struct uac_params *params = &audio_dev->params;
+	int req_len, i;
+
+	ep = audio_dev->out_ep;
+	prm = &uac->c_prm;
+	config_ep_by_speed(gadget, &audio_dev->func, ep);
+	req_len = prm->max_psize;
+
+	prm->ep_enabled = true;
+	usb_ep_enable(ep);
+
+	for (i = 0; i < params->req_number; i++) {
+		if (!prm->ureq[i].req) {
+			req = usb_ep_alloc_request(ep, GFP_ATOMIC);
+			if (req == NULL)
+				return -ENOMEM;
+
+			prm->ureq[i].req = req;
+			prm->ureq[i].pp = prm;
+
+			req->zero = 0;
+			req->context = &prm->ureq[i];
+			req->length = req_len;
+			req->complete = u_audio_iso_complete;
+			req->buf = prm->rbuf + i * prm->max_psize;
+		}
+
+		if (usb_ep_queue(ep, prm->ureq[i].req, GFP_ATOMIC))
+			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(u_audio_start_capture);
+
+void u_audio_stop_capture(struct g_audio *audio_dev)
+{
+	struct snd_uac_chip *uac = audio_dev->uac;
+
+	free_ep(&uac->c_prm, audio_dev->out_ep);
+}
+EXPORT_SYMBOL_GPL(u_audio_stop_capture);
+
+int u_audio_start_playback(struct g_audio *audio_dev)
+{
+	struct snd_uac_chip *uac = audio_dev->uac;
+	struct usb_gadget *gadget = audio_dev->gadget;
+	struct device *dev = &gadget->dev;
+	struct usb_request *req;
+	struct usb_ep *ep;
+	struct uac_rtd_params *prm;
+	struct uac_params *params = &audio_dev->params;
+	unsigned int factor, rate;
+	const struct usb_endpoint_descriptor *ep_desc;
+	int req_len, i;
+
+	ep = audio_dev->in_ep;
+	prm = &uac->p_prm;
+	config_ep_by_speed(gadget, &audio_dev->func, ep);
+
+	ep_desc = ep->desc;
+
+	/* pre-calculate the playback endpoint's interval */
+	if (gadget->speed == USB_SPEED_FULL)
+		factor = 1000;
+	else
+		factor = 8000;
+
+	/* pre-compute some values for iso_complete() */
+	uac->p_framesize = params->p_ssize *
+			    num_channels(params->p_chmask);
+	rate = params->p_srate * uac->p_framesize;
+	uac->p_interval = factor / (1 << (ep_desc->bInterval - 1));
+	uac->p_pktsize = min_t(unsigned int, rate / uac->p_interval,
+				prm->max_psize);
+
+	if (uac->p_pktsize < prm->max_psize)
+		uac->p_pktsize_residue = rate % uac->p_interval;
+	else
+		uac->p_pktsize_residue = 0;
+
+	req_len = uac->p_pktsize;
+	uac->p_residue = 0;
+
+	prm->ep_enabled = true;
+	usb_ep_enable(ep);
+
+	for (i = 0; i < params->req_number; i++) {
+		if (!prm->ureq[i].req) {
+			req = usb_ep_alloc_request(ep, GFP_ATOMIC);
+			if (req == NULL)
+				return -ENOMEM;
+
+			prm->ureq[i].req = req;
+			prm->ureq[i].pp = prm;
+
+			req->zero = 0;
+			req->context = &prm->ureq[i];
+			req->length = req_len;
+			req->complete = u_audio_iso_complete;
+			req->buf = prm->rbuf + i * prm->max_psize;
+		}
+
+		if (usb_ep_queue(ep, prm->ureq[i].req, GFP_ATOMIC))
+			dev_err(dev, "%s:%d Error!\n", __func__, __LINE__);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(u_audio_start_playback);
+
+void u_audio_stop_playback(struct g_audio *audio_dev)
+{
+	struct snd_uac_chip *uac = audio_dev->uac;
+
+	free_ep(&uac->p_prm, audio_dev->in_ep);
+}
+EXPORT_SYMBOL_GPL(u_audio_stop_playback);
+
+int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
+					const char *card_name)
+{
+	struct snd_uac_chip *uac;
+	struct snd_card *card;
+	struct snd_pcm *pcm;
+	struct uac_params *params;
+	int p_chmask, c_chmask;
+	int err;
+
+	if (!g_audio)
+		return -EINVAL;
+
+	uac = kzalloc(sizeof(*uac), GFP_KERNEL);
+	if (!uac)
+		return -ENOMEM;
+	g_audio->uac = uac;
+	uac->audio_dev = g_audio;
+
+	params = &g_audio->params;
+	p_chmask = params->p_chmask;
+	c_chmask = params->c_chmask;
+
+	if (c_chmask) {
+		struct uac_rtd_params *prm = &uac->c_prm;
+
+		uac->c_prm.uac = uac;
+		prm->max_psize = g_audio->out_ep_maxpsize;
+
+		prm->ureq = kcalloc(params->req_number, sizeof(struct uac_req),
+				GFP_KERNEL);
+		if (!prm->ureq) {
+			err = -ENOMEM;
+			goto fail;
+		}
+
+		prm->rbuf = kcalloc(params->req_number, prm->max_psize,
+				GFP_KERNEL);
+		if (!prm->rbuf) {
+			prm->max_psize = 0;
+			err = -ENOMEM;
+			goto fail;
+		}
+	}
+
+	if (p_chmask) {
+		struct uac_rtd_params *prm = &uac->p_prm;
+
+		uac->p_prm.uac = uac;
+		prm->max_psize = g_audio->in_ep_maxpsize;
+
+		prm->ureq = kcalloc(params->req_number, sizeof(struct uac_req),
+				GFP_KERNEL);
+		if (!prm->ureq) {
+			err = -ENOMEM;
+			goto fail;
+		}
+
+		prm->rbuf = kcalloc(params->req_number, prm->max_psize,
+				GFP_KERNEL);
+		if (!prm->rbuf) {
+			prm->max_psize = 0;
+			err = -ENOMEM;
+			goto fail;
+		}
+	}
+
+	/* Choose any slot, with no id */
+	err = snd_card_new(&g_audio->gadget->dev,
+			-1, NULL, THIS_MODULE, 0, &card);
+	if (err < 0)
+		goto fail;
+
+	uac->card = card;
+
+	/*
+	 * Create first PCM device
+	 * Create a substream only for non-zero channel streams
+	 */
+	err = snd_pcm_new(uac->card, pcm_name, 0,
+			       p_chmask ? 1 : 0, c_chmask ? 1 : 0, &pcm);
+	if (err < 0)
+		goto snd_fail;
+
+	strcpy(pcm->name, pcm_name);
+	pcm->private_data = uac;
+	uac->pcm = pcm;
+
+	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &uac_pcm_ops);
+	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &uac_pcm_ops);
+
+	strcpy(card->driver, card_name);
+	strcpy(card->shortname, card_name);
+	sprintf(card->longname, "%s %i", card_name, card->dev->id);
+
+	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_CONTINUOUS,
+		snd_dma_continuous_data(GFP_KERNEL), 0, BUFF_SIZE_MAX);
+
+	err = snd_card_register(card);
+
+	if (!err)
+		return 0;
+
+snd_fail:
+	snd_card_free(card);
+fail:
+	kfree(uac->p_prm.ureq);
+	kfree(uac->c_prm.ureq);
+	kfree(uac->p_prm.rbuf);
+	kfree(uac->c_prm.rbuf);
+	kfree(uac);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(g_audio_setup);
+
+void g_audio_cleanup(struct g_audio *g_audio)
+{
+	struct snd_uac_chip *uac;
+	struct snd_card *card;
+
+	if (!g_audio || !g_audio->uac)
+		return;
+
+	uac = g_audio->uac;
+	card = uac->card;
+	if (card)
+		snd_card_free(card);
+
+	kfree(uac->p_prm.ureq);
+	kfree(uac->c_prm.ureq);
+	kfree(uac->p_prm.rbuf);
+	kfree(uac->c_prm.rbuf);
+	kfree(uac);
+}
+EXPORT_SYMBOL_GPL(g_audio_cleanup);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("USB gadget \"ALSA sound card\" utilities");
+MODULE_AUTHOR("Ruslan Bilovol");

drivers/usb/gadget/function/u_audio.h

···
+/*
+ * u_audio.h -- interface to USB gadget "ALSA sound card" utilities
+ *
+ * Copyright (C) 2016
+ * Author: Ruslan Bilovol <[e-mail]>
+ *
+ * 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.
+ *
+ */
+
+#ifndef __U_AUDIO_H
+#define __U_AUDIO_H
+
+#include <linux/usb/composite.h>
+
+struct uac_params {
+	/* playback */
+	int p_chmask;	/* channel mask */
+	int p_srate;	/* rate in Hz */
+	int p_ssize;	/* sample size */
+
+	/* capture */
+	int c_chmask;	/* channel mask */
+	int c_srate;	/* rate in Hz */
+	int c_ssize;	/* sample size */
+
+	int req_number; /* number of preallocated requests */
+};
+
+struct g_audio {
+	struct usb_function func;
+	struct usb_gadget *gadget;
+
+	struct usb_ep *in_ep;
+	struct usb_ep *out_ep;
+
+	/* Max packet size for all in_ep possible speeds */
+	unsigned int in_ep_maxpsize;
+	/* Max packet size for all out_ep possible speeds */
+	unsigned int out_ep_maxpsize;
+
+	/* The ALSA Sound Card it represents on the USB-Client side */
+	struct snd_uac_chip *uac;
+
+	struct uac_params params;
+};
+
+static inline struct g_audio *func_to_g_audio(struct usb_function *f)
+{
+	return container_of(f, struct g_audio, func);
+}
+
+static inline uint num_channels(uint chanmask)
+{
+	uint num = 0;
+
+	while (chanmask) {
+		num += (chanmask & 1);
+		chanmask >>= 1;
+	}
+
+	return num;
+}
+
+/*
+ * g_audio_setup - initialize one virtual ALSA sound card
+ * @g_audio: struct with filled params, in_ep_maxpsize, out_ep_maxpsize
+ * @pcm_name: the id string for a PCM instance of this sound card
+ * @card_name: name of this soundcard
+ *
+ * This sets up the single virtual ALSA sound card that may be exported by a
+ * gadget driver using this framework.
+ *
+ * Context: may sleep
+ *
+ * Returns zero on success, or a negative error on failure.
+ */
+int g_audio_setup(struct g_audio *g_audio, const char *pcm_name,
+					const char *card_name);
+void g_audio_cleanup(struct g_audio *g_audio);
+
+int u_audio_start_capture(struct g_audio *g_audio);
+void u_audio_stop_capture(struct g_audio *g_audio);
+int u_audio_start_playback(struct g_audio *g_audio);
+void u_audio_stop_playback(struct g_audio *g_audio);
+
+#endif /* __U_AUDIO_H */

drivers/usb/gadget/legacy/Kconfig

···
 	select SND_PCM
 	select USB_F_UAC1 if GADGET_UAC1
 	select USB_F_UAC2 if !GADGET_UAC1
+	select USB_U_AUDIO if USB_F_UAC2
 	help
 	  This Gadget Audio driver is compatible with USB Audio Class
 	  specification 2.0. It implements 1 AudioControl interface,