drivers/usb/gadget/f_midi.c

/*
 * f_midi.c -- USB MIDI class function driver
 *
 * Copyright (C) 2006 Thumtronics Pty Ltd.
 * Developed for Thumtronics by Grey Innovation
 * Ben Williamson <ben.williamson@greyinnovation.com>
 *
 * Rewritten for the composite framework
 *   Copyright (C) 2011 Daniel Mack <zonque@gmail.com>
 *
 * Based on drivers/usb/gadget/f_audio.c,
 *   Copyright (C) 2008 Bryan Wu <cooloney@kernel.org>
 *   Copyright (C) 2008 Analog Devices, Inc
 *
 * and drivers/usb/gadget/midi.c,
 *   Copyright (C) 2006 Thumtronics Pty Ltd.
 *   Ben Williamson <ben.williamson@greyinnovation.com>
 *
 * Licensed under the GPL-2 or later.
 */

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/utsname.h>
#include <linux/device.h>

#include <sound/core.h>
#include <sound/initval.h>
#include <sound/rawmidi.h>

#include <linux/usb/ch9.h>
#include <linux/usb/gadget.h>
#include <linux/usb/audio.h>
#include <linux/usb/midi.h>

MODULE_AUTHOR("Ben Williamson");
MODULE_LICENSE("GPL v2");

static const char f_midi_shortname[] = "f_midi";
static const char f_midi_longname[] = "MIDI Gadget";

/*
 * We can only handle 16 cables on one single endpoint, as cable numbers are
 * stored in 4-bit fields. And as the interface currently only holds one
 * single endpoint, this is the maximum number of ports we can allow.
 */
#define MAX_PORTS 16

/*
 * This is a gadget, and the IN/OUT naming is from the host's perspective.
 * USB -> OUT endpoint -> rawmidi
 * USB <- IN endpoint  <- rawmidi
 */
struct gmidi_in_port {
	struct f_midi *midi;
	int active;
	uint8_t cable;
	uint8_t state;
#define STATE_UNKNOWN	0
#define STATE_1PARAM	1
#define STATE_2PARAM_1	2
#define STATE_2PARAM_2	3
#define STATE_SYSEX_0	4
#define STATE_SYSEX_1	5
#define STATE_SYSEX_2	6
	uint8_t data[2];
};

struct f_midi {
	struct usb_function	func;
	struct usb_gadget	*gadget;
	struct usb_ep		*in_ep, *out_ep;
	struct snd_card		*card;
	struct snd_rawmidi	*rmidi;

	struct snd_rawmidi_substream *in_substream[MAX_PORTS];
	struct snd_rawmidi_substream *out_substream[MAX_PORTS];
	struct gmidi_in_port	*in_port[MAX_PORTS];

	unsigned long		out_triggered;
	struct tasklet_struct	tasklet;
	unsigned int in_ports;
	unsigned int out_ports;
	int index;
	char *id;
	unsigned int buflen, qlen;
};

static inline struct f_midi *func_to_midi(struct usb_function *f)
{
	return container_of(f, struct f_midi, func);
}

static void f_midi_transmit(struct f_midi *midi, struct usb_request *req);

DECLARE_UAC_AC_HEADER_DESCRIPTOR(1);
DECLARE_USB_MIDI_OUT_JACK_DESCRIPTOR(1);
DECLARE_USB_MIDI_OUT_JACK_DESCRIPTOR(16);
DECLARE_USB_MS_ENDPOINT_DESCRIPTOR(16);

/* B.3.1  Standard AC Interface Descriptor */
static struct usb_interface_descriptor ac_interface_desc __initdata = {
	.bLength =		USB_DT_INTERFACE_SIZE,
	.bDescriptorType =	USB_DT_INTERFACE,
	/* .bInterfaceNumber =	DYNAMIC */
	/* .bNumEndpoints =	DYNAMIC */
	.bInterfaceClass =	USB_CLASS_AUDIO,
	.bInterfaceSubClass =	USB_SUBCLASS_AUDIOCONTROL,
	/* .iInterface =	DYNAMIC */
};

/* B.3.2  Class-Specific AC Interface Descriptor */
static struct uac1_ac_header_descriptor_1 ac_header_desc __initdata = {
	.bLength =		UAC_DT_AC_HEADER_SIZE(1),
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubtype =	USB_MS_HEADER,
	.bcdADC =		cpu_to_le16(0x0100),
	.wTotalLength =		cpu_to_le16(UAC_DT_AC_HEADER_SIZE(1)),
	.bInCollection =	1,
	/* .baInterfaceNr =	DYNAMIC */
};

/* B.4.1  Standard MS Interface Descriptor */
static struct usb_interface_descriptor ms_interface_desc __initdata = {
	.bLength =		USB_DT_INTERFACE_SIZE,
	.bDescriptorType =	USB_DT_INTERFACE,
	/* .bInterfaceNumber =	DYNAMIC */
	.bNumEndpoints =	2,
	.bInterfaceClass =	USB_CLASS_AUDIO,
	.bInterfaceSubClass =	USB_SUBCLASS_MIDISTREAMING,
	/* .iInterface =	DYNAMIC */
};

/* B.4.2  Class-Specific MS Interface Descriptor */
static struct usb_ms_header_descriptor ms_header_desc __initdata = {
	.bLength =		USB_DT_MS_HEADER_SIZE,
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubtype =	USB_MS_HEADER,
	.bcdMSC =		cpu_to_le16(0x0100),
	/* .wTotalLength =	DYNAMIC */
};

/* B.4.3  Embedded MIDI IN Jack Descriptor */
static struct usb_midi_in_jack_descriptor jack_in_emb_desc = {
	.bLength =	      USB_DT_MIDI_IN_SIZE,
	.bDescriptorType =      USB_DT_CS_INTERFACE,
	.bDescriptorSubtype =   USB_MS_MIDI_IN_JACK,
	.bJackType =	    USB_MS_EMBEDDED,
	/* .bJackID =		DYNAMIC */
};

/* B.4.4  Embedded MIDI OUT Jack Descriptor */
static struct usb_midi_out_jack_descriptor_16 jack_out_emb_desc = {
	/* .bLength =		DYNAMIC */
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubtype =	USB_MS_MIDI_OUT_JACK,
	.bJackType =		USB_MS_EMBEDDED,
	/* .bJackID =		DYNAMIC */
	/* .bNrInputPins =	DYNAMIC */
	/* .pins =		DYNAMIC */
};

/* B.5.1  Standard Bulk OUT Endpoint Descriptor */
static struct usb_endpoint_descriptor bulk_out_desc = {
	.bLength =		USB_DT_ENDPOINT_AUDIO_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_OUT,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
};

/* B.5.2  Class-specific MS Bulk OUT Endpoint Descriptor */
static struct usb_ms_endpoint_descriptor_16 ms_out_desc = {
	/* .bLength =		DYNAMIC */
	.bDescriptorType =	USB_DT_CS_ENDPOINT,
	.bDescriptorSubtype =	USB_MS_GENERAL,
	/* .bNumEmbMIDIJack =	DYNAMIC */
	/* .baAssocJackID =	DYNAMIC */
};

/* B.6.1  Standard Bulk IN Endpoint Descriptor */
static struct usb_endpoint_descriptor bulk_in_desc = {
	.bLength =		USB_DT_ENDPOINT_AUDIO_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_IN,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
};

/* B.6.2  Class-specific MS Bulk IN Endpoint Descriptor */
static struct usb_ms_endpoint_descriptor_16 ms_in_desc = {
	/* .bLength =		DYNAMIC */
	.bDescriptorType =	USB_DT_CS_ENDPOINT,
	.bDescriptorSubtype =	USB_MS_GENERAL,
	/* .bNumEmbMIDIJack =	DYNAMIC */
	/* .baAssocJackID =	DYNAMIC */
};

/* string IDs are assigned dynamically */

#define STRING_FUNC_IDX			0

static struct usb_string midi_string_defs[] = {
	[STRING_FUNC_IDX].s = "MIDI function",
	{  } /* end of list */
};

static struct usb_gadget_strings midi_stringtab = {
	.language	= 0x0409,	/* en-us */
	.strings	= midi_string_defs,
};

static struct usb_gadget_strings *midi_strings[] = {
	&midi_stringtab,
	NULL,
};

static struct usb_request *alloc_ep_req(struct usb_ep *ep, unsigned length)
{
	struct usb_request *req;

	req = usb_ep_alloc_request(ep, GFP_ATOMIC);
	if (req) {
		req->length = length;
		req->buf = kmalloc(length, GFP_ATOMIC);
		if (!req->buf) {
			usb_ep_free_request(ep, req);
			req = NULL;
		}
	}
	return req;
}

static void free_ep_req(struct usb_ep *ep, struct usb_request *req)
{
	kfree(req->buf);
	usb_ep_free_request(ep, req);
}

static const uint8_t f_midi_cin_length[] = {
	0, 0, 2, 3, 3, 1, 2, 3, 3, 3, 3, 3, 2, 2, 3, 1
};

/*
 * Receives a chunk of MIDI data.
 */
static void f_midi_read_data(struct usb_ep *ep, int cable,
			     uint8_t *data, int length)
{
	struct f_midi *midi = ep->driver_data;
	struct snd_rawmidi_substream *substream = midi->out_substream[cable];

	if (!substream)
		/* Nobody is listening - throw it on the floor. */
		return;

	if (!test_bit(cable, &midi->out_triggered))
		return;

	snd_rawmidi_receive(substream, data, length);
}

static void f_midi_handle_out_data(struct usb_ep *ep, struct usb_request *req)
{
	unsigned int i;
	u8 *buf = req->buf;

	for (i = 0; i + 3 < req->actual; i += 4)
		if (buf[i] != 0) {
			int cable = buf[i] >> 4;
			int length = f_midi_cin_length[buf[i] & 0x0f];
			f_midi_read_data(ep, cable, &buf[i + 1], length);
		}
}

static void
f_midi_complete(struct usb_ep *ep, struct usb_request *req)
{
	struct f_midi *midi = ep->driver_data;
	struct usb_composite_dev *cdev = midi->func.config->cdev;
	int status = req->status;

	switch (status) {
	case 0:			 /* normal completion */
		if (ep == midi->out_ep) {
			/* We received stuff. req is queued again, below */
			f_midi_handle_out_data(ep, req);
		} else if (ep == midi->in_ep) {
			/* Our transmit completed. See if there's more to go.
			 * f_midi_transmit eats req, don't queue it again. */
			f_midi_transmit(midi, req);
			return;
		}
		break;

	/* this endpoint is normally active while we're configured */
	case -ECONNABORTED:	/* hardware forced ep reset */
	case -ECONNRESET:	/* request dequeued */
	case -ESHUTDOWN:	/* disconnect from host */
		VDBG(cdev, "%s gone (%d), %d/%d\n", ep->name, status,
				req->actual, req->length);
		if (ep == midi->out_ep)
			f_midi_handle_out_data(ep, req);

		free_ep_req(ep, req);
		return;

	case -EOVERFLOW:	/* buffer overrun on read means that
				 * we didn't provide a big enough buffer.
				 */
	default:
		DBG(cdev, "%s complete --> %d, %d/%d\n", ep->name,
				status, req->actual, req->length);
		break;
	case -EREMOTEIO:	/* short read */
		break;
	}

	status = usb_ep_queue(ep, req, GFP_ATOMIC);
	if (status) {
		ERROR(cdev, "kill %s:  resubmit %d bytes --> %d\n",
				ep->name, req->length, status);
		usb_ep_set_halt(ep);
		/* FIXME recover later ... somehow */
	}
}

static int f_midi_start_ep(struct f_midi *midi,
			   struct usb_function *f,
			   struct usb_ep *ep)
{
	int err;
	struct usb_composite_dev *cdev = f->config->cdev;

	if (ep->driver_data)
		usb_ep_disable(ep);

	err = config_ep_by_speed(midi->gadget, f, ep);
	if (err) {
		ERROR(cdev, "can't configure %s: %d\n", ep->name, err);
		return err;
	}

	err = usb_ep_enable(ep);
	if (err) {
		ERROR(cdev, "can't start %s: %d\n", ep->name, err);
		return err;
	}

	ep->driver_data = midi;

	return 0;
}

static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
{
	struct f_midi *midi = func_to_midi(f);
	struct usb_composite_dev *cdev = f->config->cdev;
	unsigned i;
	int err;

	err = f_midi_start_ep(midi, f, midi->in_ep);
	if (err)
		return err;

	err = f_midi_start_ep(midi, f, midi->out_ep);
	if (err)
		return err;

	if (midi->out_ep->driver_data)
		usb_ep_disable(midi->out_ep);

	err = config_ep_by_speed(midi->gadget, f, midi->out_ep);
	if (err) {
		ERROR(cdev, "can't configure %s: %d\n",
		      midi->out_ep->name, err);
		return err;
	}

	err = usb_ep_enable(midi->out_ep);
	if (err) {
		ERROR(cdev, "can't start %s: %d\n",
		      midi->out_ep->name, err);
		return err;
	}

	midi->out_ep->driver_data = midi;

	/* allocate a bunch of read buffers and queue them all at once. */
	for (i = 0; i < midi->qlen && err == 0; i++) {
		struct usb_request *req =
			alloc_ep_req(midi->out_ep, midi->buflen);
		if (req == NULL)
			return -ENOMEM;

		req->complete = f_midi_complete;
		err = usb_ep_queue(midi->out_ep, req, GFP_ATOMIC);
		if (err) {
			ERROR(midi, "%s queue req: %d\n",
				    midi->out_ep->name, err);
		}
	}

	return 0;
}

static void f_midi_disable(struct usb_function *f)
{
	struct f_midi *midi = func_to_midi(f);
	struct usb_composite_dev *cdev = f->config->cdev;

	DBG(cdev, "disable\n");

	/*
	 * just disable endpoints, forcing completion of pending i/o.
	 * all our completion handlers free their requests in this case.
	 */
	usb_ep_disable(midi->in_ep);
	usb_ep_disable(midi->out_ep);
}

static void f_midi_unbind(struct usb_configuration *c, struct usb_function *f)
{
	struct usb_composite_dev *cdev = f->config->cdev;
	struct f_midi *midi = func_to_midi(f);
	struct snd_card *card;

	DBG(cdev, "unbind\n");

	/* just to be sure */
	f_midi_disable(f);

	card = midi->card;
	midi->card = NULL;
	if (card)
		snd_card_free(card);

	kfree(midi->id);
	midi->id = NULL;

	usb_free_descriptors(f->descriptors);
	kfree(midi);
}

static int f_midi_snd_free(struct snd_device *device)
{
	return 0;
}

static void f_midi_transmit_packet(struct usb_request *req, uint8_t p0,
					uint8_t p1, uint8_t p2, uint8_t p3)
{
	unsigned length = req->length;
	u8 *buf = (u8 *)req->buf + length;

	buf[0] = p0;
	buf[1] = p1;
	buf[2] = p2;
	buf[3] = p3;
	req->length = length + 4;
}

/*
 * Converts MIDI commands to USB MIDI packets.
 */
static void f_midi_transmit_byte(struct usb_request *req,
				 struct gmidi_in_port *port, uint8_t b)
{
	uint8_t p0 = port->cable << 4;

	if (b >= 0xf8) {
		f_midi_transmit_packet(req, p0 | 0x0f, b, 0, 0);
	} else if (b >= 0xf0) {
		switch (b) {
		case 0xf0:
			port->data[0] = b;
			port->state = STATE_SYSEX_1;
			break;
		case 0xf1:
		case 0xf3:
			port->data[0] = b;
			port->state = STATE_1PARAM;
			break;
		case 0xf2:
			port->data[0] = b;
			port->state = STATE_2PARAM_1;
			break;
		case 0xf4:
		case 0xf5:
			port->state = STATE_UNKNOWN;
			break;
		case 0xf6:
			f_midi_transmit_packet(req, p0 | 0x05, 0xf6, 0, 0);
			port->state = STATE_UNKNOWN;
			break;
		case 0xf7:
			switch (port->state) {
			case STATE_SYSEX_0:
				f_midi_transmit_packet(req,
					p0 | 0x05, 0xf7, 0, 0);
				break;
			case STATE_SYSEX_1:
				f_midi_transmit_packet(req,
					p0 | 0x06, port->data[0], 0xf7, 0);
				break;
			case STATE_SYSEX_2:
				f_midi_transmit_packet(req,
					p0 | 0x07, port->data[0],
					port->data[1], 0xf7);
				break;
			}
			port->state = STATE_UNKNOWN;
			break;
		}
	} else if (b >= 0x80) {
		port->data[0] = b;
		if (b >= 0xc0 && b <= 0xdf)
			port->state = STATE_1PARAM;
		else
			port->state = STATE_2PARAM_1;
	} else { /* b < 0x80 */
		switch (port->state) {
		case STATE_1PARAM:
			if (port->data[0] < 0xf0) {
				p0 |= port->data[0] >> 4;
			} else {
				p0 |= 0x02;
				port->state = STATE_UNKNOWN;
			}
			f_midi_transmit_packet(req, p0, port->data[0], b, 0);
			break;
		case STATE_2PARAM_1:
			port->data[1] = b;
			port->state = STATE_2PARAM_2;
			break;
		case STATE_2PARAM_2:
			if (port->data[0] < 0xf0) {
				p0 |= port->data[0] >> 4;
				port->state = STATE_2PARAM_1;
			} else {
				p0 |= 0x03;
				port->state = STATE_UNKNOWN;
			}
			f_midi_transmit_packet(req,
				p0, port->data[0], port->data[1], b);
			break;
		case STATE_SYSEX_0:
			port->data[0] = b;
			port->state = STATE_SYSEX_1;
			break;
		case STATE_SYSEX_1:
			port->data[1] = b;
			port->state = STATE_SYSEX_2;
			break;
		case STATE_SYSEX_2:
			f_midi_transmit_packet(req,
				p0 | 0x04, port->data[0], port->data[1], b);
			port->state = STATE_SYSEX_0;
			break;
		}
	}
}

static void f_midi_transmit(struct f_midi *midi, struct usb_request *req)
{
	struct usb_ep *ep = midi->in_ep;
	int i;

	if (!ep)
		return;

	if (!req)
		req = alloc_ep_req(ep, midi->buflen);

	if (!req) {
		ERROR(midi, "gmidi_transmit: alloc_ep_request failed\n");
		return;
	}
	req->length = 0;
	req->complete = f_midi_complete;

	for (i = 0; i < MAX_PORTS; i++) {
		struct gmidi_in_port *port = midi->in_port[i];
		struct snd_rawmidi_substream *substream = midi->in_substream[i];

		if (!port || !port->active || !substream)
			continue;

		while (req->length + 3 < midi->buflen) {
			uint8_t b;
			if (snd_rawmidi_transmit(substream, &b, 1) != 1) {
				port->active = 0;
				break;
			}
			f_midi_transmit_byte(req, port, b);
		}
	}

	if (req->length > 0)
		usb_ep_queue(ep, req, GFP_ATOMIC);
	else
		free_ep_req(ep, req);
}

static void f_midi_in_tasklet(unsigned long data)
{
	struct f_midi *midi = (struct f_midi *) data;
	f_midi_transmit(midi, NULL);
}

static int f_midi_in_open(struct snd_rawmidi_substream *substream)
{
	struct f_midi *midi = substream->rmidi->private_data;

	if (!midi->in_port[substream->number])
		return -EINVAL;

	VDBG(midi, "%s()\n", __func__);
	midi->in_substream[substream->number] = substream;
	midi->in_port[substream->number]->state = STATE_UNKNOWN;
	return 0;
}

static int f_midi_in_close(struct snd_rawmidi_substream *substream)
{
	struct f_midi *midi = substream->rmidi->private_data;

	VDBG(midi, "%s()\n", __func__);
	return 0;
}

static void f_midi_in_trigger(struct snd_rawmidi_substream *substream, int up)
{
	struct f_midi *midi = substream->rmidi->private_data;

	if (!midi->in_port[substream->number])
		return;

	VDBG(midi, "%s() %d\n", __func__, up);
	midi->in_port[substream->number]->active = up;
	if (up)
		tasklet_hi_schedule(&midi->tasklet);
}

static int f_midi_out_open(struct snd_rawmidi_substream *substream)
{
	struct f_midi *midi = substream->rmidi->private_data;

	if (substream->number >= MAX_PORTS)
		return -EINVAL;

	VDBG(midi, "%s()\n", __func__);
	midi->out_substream[substream->number] = substream;
	return 0;
}

static int f_midi_out_close(struct snd_rawmidi_substream *substream)
{
	struct f_midi *midi = substream->rmidi->private_data;

	VDBG(midi, "%s()\n", __func__);
	return 0;
}

static void f_midi_out_trigger(struct snd_rawmidi_substream *substream, int up)
{
	struct f_midi *midi = substream->rmidi->private_data;

	VDBG(midi, "%s()\n", __func__);

	if (up)
		set_bit(substream->number, &midi->out_triggered);
	else
		clear_bit(substream->number, &midi->out_triggered);
}

static struct snd_rawmidi_ops gmidi_in_ops = {
	.open = f_midi_in_open,
	.close = f_midi_in_close,
	.trigger = f_midi_in_trigger,
};

static struct snd_rawmidi_ops gmidi_out_ops = {
	.open = f_midi_out_open,
	.close = f_midi_out_close,
	.trigger = f_midi_out_trigger
};

/* register as a sound "card" */
static int f_midi_register_card(struct f_midi *midi)
{
	struct snd_card *card;
	struct snd_rawmidi *rmidi;
	int err;
	static struct snd_device_ops ops = {
		.dev_free = f_midi_snd_free,
	};

	err = snd_card_create(midi->index, midi->id, THIS_MODULE, 0, &card);
	if (err < 0) {
		ERROR(midi, "snd_card_create() failed\n");
		goto fail;
	}
	midi->card = card;

	err = snd_device_new(card, SNDRV_DEV_LOWLEVEL, midi, &ops);
	if (err < 0) {
		ERROR(midi, "snd_device_new() failed: error %d\n", err);
		goto fail;
	}

	strcpy(card->driver, f_midi_longname);
	strcpy(card->longname, f_midi_longname);
	strcpy(card->shortname, f_midi_shortname);

	/* Set up rawmidi */
	snd_component_add(card, "MIDI");
	err = snd_rawmidi_new(card, card->longname, 0,
			      midi->out_ports, midi->in_ports, &rmidi);
	if (err < 0) {
		ERROR(midi, "snd_rawmidi_new() failed: error %d\n", err);
		goto fail;
	}
	midi->rmidi = rmidi;
	strcpy(rmidi->name, card->shortname);
	rmidi->info_flags = SNDRV_RAWMIDI_INFO_OUTPUT |
			    SNDRV_RAWMIDI_INFO_INPUT |
			    SNDRV_RAWMIDI_INFO_DUPLEX;
	rmidi->private_data = midi;

	/*
	 * Yes, rawmidi OUTPUT = USB IN, and rawmidi INPUT = USB OUT.
	 * It's an upside-down world being a gadget.
	 */
	snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_OUTPUT, &gmidi_in_ops);
	snd_rawmidi_set_ops(rmidi, SNDRV_RAWMIDI_STREAM_INPUT, &gmidi_out_ops);

	snd_card_set_dev(card, &midi->gadget->dev);

	/* register it - we're ready to go */
	err = snd_card_register(card);
	if (err < 0) {
		ERROR(midi, "snd_card_register() failed\n");
		goto fail;
	}

	VDBG(midi, "%s() finished ok\n", __func__);
	return 0;

fail:
	if (midi->card) {
		snd_card_free(midi->card);
		midi->card = NULL;
	}
	return err;
}

/* MIDI function driver setup/binding */

static int __init
f_midi_bind(struct usb_configuration *c, struct usb_function *f)
{
	struct usb_descriptor_header *midi_function[(MAX_PORTS * 2) + 12];
	struct usb_midi_in_jack_descriptor jack_in_ext_desc[MAX_PORTS];
	struct usb_midi_out_jack_descriptor_1 jack_out_ext_desc[MAX_PORTS];
	struct usb_composite_dev *cdev = c->cdev;
	struct f_midi *midi = func_to_midi(f);
	int status, n, jack = 1, i = 0;

	/* maybe allocate device-global string ID */
	if (midi_string_defs[0].id == 0) {
		status = usb_string_id(c->cdev);
		if (status < 0)
			goto fail;
		midi_string_defs[0].id = status;
	}

	/* We have two interfaces, AudioControl and MIDIStreaming */
	status = usb_interface_id(c, f);
	if (status < 0)
		goto fail;
	ac_interface_desc.bInterfaceNumber = status;

	status = usb_interface_id(c, f);
	if (status < 0)
		goto fail;
	ms_interface_desc.bInterfaceNumber = status;
	ac_header_desc.baInterfaceNr[0] = status;

	status = -ENODEV;

	/* allocate instance-specific endpoints */
	midi->in_ep = usb_ep_autoconfig(cdev->gadget, &bulk_in_desc);
	if (!midi->in_ep)
		goto fail;
	midi->in_ep->driver_data = cdev;	/* claim */

	midi->out_ep = usb_ep_autoconfig(cdev->gadget, &bulk_out_desc);
	if (!midi->out_ep)
		goto fail;
	midi->out_ep->driver_data = cdev;	/* claim */

	/*
	 * construct the function's descriptor set. As the number of
	 * input and output MIDI ports is configurable, we have to do
	 * it that way.
	 */

	/* add the headers - these are always the same */
	midi_function[i++] = (struct usb_descriptor_header *) &ac_interface_desc;
	midi_function[i++] = (struct usb_descriptor_header *) &ac_header_desc;
	midi_function[i++] = (struct usb_descriptor_header *) &ms_interface_desc;

	/* calculate the header's wTotalLength */
	n = USB_DT_MS_HEADER_SIZE
		+ (1 + midi->in_ports) * USB_DT_MIDI_IN_SIZE
		+ (1 + midi->out_ports) * USB_DT_MIDI_OUT_SIZE(1);
	ms_header_desc.wTotalLength = cpu_to_le16(n);

	midi_function[i++] = (struct usb_descriptor_header *) &ms_header_desc;

	/* we have one embedded IN jack */
	jack_in_emb_desc.bJackID = jack++;
	midi_function[i++] = (struct usb_descriptor_header *) &jack_in_emb_desc;

	/* and a dynamic amount of external IN jacks */
	for (n = 0; n < midi->in_ports; n++) {
		struct usb_midi_in_jack_descriptor *ext = &jack_in_ext_desc[n];

		ext->bLength =			USB_DT_MIDI_IN_SIZE;
		ext->bDescriptorType =		USB_DT_CS_INTERFACE;
		ext->bDescriptorSubtype =	USB_MS_MIDI_IN_JACK;
		ext->bJackType =		USB_MS_EXTERNAL;
		ext->bJackID =			jack++;
		ext->iJack =			0;

		midi_function[i++] = (struct usb_descriptor_header *) ext;
	}

	/* one embedded OUT jack ... */
	jack_out_emb_desc.bLength = USB_DT_MIDI_OUT_SIZE(midi->in_ports);
	jack_out_emb_desc.bJackID = jack++;
	jack_out_emb_desc.bNrInputPins = midi->in_ports;
	/* ... which referencess all external IN jacks */
	for (n = 0; n < midi->in_ports; n++) {
		jack_out_emb_desc.pins[n].baSourceID = jack_in_ext_desc[n].bJackID;
		jack_out_emb_desc.pins[n].baSourcePin =	1;
	}

	midi_function[i++] = (struct usb_descriptor_header *) &jack_out_emb_desc;

	/* and multiple external OUT jacks ... */
	for (n = 0; n < midi->out_ports; n++) {
		struct usb_midi_out_jack_descriptor_1 *ext = &jack_out_ext_desc[n];
		int m;

		ext->bLength =			USB_DT_MIDI_OUT_SIZE(1);
		ext->bDescriptorType =		USB_DT_CS_INTERFACE;
		ext->bDescriptorSubtype =	USB_MS_MIDI_OUT_JACK;
		ext->bJackType =		USB_MS_EXTERNAL;
		ext->bJackID =			jack++;
		ext->bNrInputPins =		1;
		ext->iJack =			0;
		/* ... which all reference the same embedded IN jack */
		for (m = 0; m < midi->out_ports; m++) {
			ext->pins[m].baSourceID =	jack_in_emb_desc.bJackID;
			ext->pins[m].baSourcePin =	1;
		}

		midi_function[i++] = (struct usb_descriptor_header *) ext;
	}

	/* configure the endpoint descriptors ... */
	ms_out_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->in_ports);
	ms_out_desc.bNumEmbMIDIJack = midi->in_ports;
	for (n = 0; n < midi->in_ports; n++)
		ms_out_desc.baAssocJackID[n] = jack_in_emb_desc.bJackID;

	ms_in_desc.bLength = USB_DT_MS_ENDPOINT_SIZE(midi->out_ports);
	ms_in_desc.bNumEmbMIDIJack = midi->out_ports;
	for (n = 0; n < midi->out_ports; n++)
		ms_in_desc.baAssocJackID[n] = jack_out_emb_desc.bJackID;

	/* ... and add them to the list */
	midi_function[i++] = (struct usb_descriptor_header *) &bulk_out_desc;
	midi_function[i++] = (struct usb_descriptor_header *) &ms_out_desc;
	midi_function[i++] = (struct usb_descriptor_header *) &bulk_in_desc;
	midi_function[i++] = (struct usb_descriptor_header *) &ms_in_desc;
	midi_function[i++] = NULL;

	/*
	 * support all relevant hardware speeds... we expect that when
	 * hardware is dual speed, all bulk-capable endpoints work at
	 * both speeds
	 */
	/* copy descriptors, and track endpoint copies */
	if (gadget_is_dualspeed(c->cdev->gadget)) {
		c->highspeed = true;
		bulk_in_desc.wMaxPacketSize = cpu_to_le16(512);
		bulk_out_desc.wMaxPacketSize = cpu_to_le16(512);
		f->hs_descriptors = usb_copy_descriptors(midi_function);
	} else {
		f->descriptors = usb_copy_descriptors(midi_function);
	}

	return 0;

fail:
	/* we might as well release our claims on endpoints */
	if (midi->out_ep)
		midi->out_ep->driver_data = NULL;
	if (midi->in_ep)
		midi->in_ep->driver_data = NULL;

	ERROR(cdev, "%s: can't bind, err %d\n", f->name, status);

	return status;
}

/**
 * f_midi_bind_config - add USB MIDI function to a configuration
 * @c: the configuration to supcard the USB audio function
 * @index: the soundcard index to use for the ALSA device creation
 * @id: the soundcard id to use for the ALSA device creation
 * @buflen: the buffer length to use
 * @qlen the number of read requests to pre-allocate
 * Context: single threaded during gadget setup
 *
 * Returns zero on success, else negative errno.
 */
int __init f_midi_bind_config(struct usb_configuration *c,
			      int index, char *id,
			      unsigned int in_ports,
			      unsigned int out_ports,
			      unsigned int buflen,
			      unsigned int qlen)
{
	struct f_midi *midi;
	int status, i;

	/* sanity check */
	if (in_ports > MAX_PORTS || out_ports > MAX_PORTS)
		return -EINVAL;

	/* allocate and initialize one new instance */
	midi = kzalloc(sizeof *midi, GFP_KERNEL);
	if (!midi) {
		status = -ENOMEM;
		goto fail;
	}

	for (i = 0; i < in_ports; i++) {
		struct gmidi_in_port *port = kzalloc(sizeof(*port), GFP_KERNEL);
		if (!port) {
			status = -ENOMEM;
			goto fail;
		}

		port->midi = midi;
		port->active = 0;
		port->cable = i;
		midi->in_port[i] = port;
	}

	midi->gadget = c->cdev->gadget;
	tasklet_init(&midi->tasklet, f_midi_in_tasklet, (unsigned long) midi);

	/* set up ALSA midi devices */
	midi->in_ports = in_ports;
	midi->out_ports = out_ports;
	status = f_midi_register_card(midi);
	if (status < 0)
		goto setup_fail;

	midi->func.name        = "gmidi function";
	midi->func.strings     = midi_strings;
	midi->func.bind        = f_midi_bind;
	midi->func.unbind      = f_midi_unbind;
	midi->func.set_alt     = f_midi_set_alt;
	midi->func.disable     = f_midi_disable;

	midi->id = kstrdup(id, GFP_KERNEL);
	midi->index = index;
	midi->buflen = buflen;
	midi->qlen = qlen;

	status = usb_add_function(c, &midi->func);
	if (status)
		goto setup_fail;

	return 0;

setup_fail:
	kfree(midi);
fail:
	return status;
}