USB: gadget: add HID gadget driver

g_hid is a USB gadget driver implementing the Human Interface Device class
specification. The driver handles basic HID protocol handling in the
kernel, and allows userspace to read/write HID reports trough /dev/hidgX
character devices.
Signed-off-by: Fabien Chouteau <fabien.chouteau@barco.com>
Signed-off-by: Peter Korsgaard <peter.korsgaard@barco.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Documentation/usb/gadget_hid.txt

+
+		     Linux USB HID gadget driver
+
+Introduction
+
+	The HID Gadget driver provides emulation of USB Human Interface
+	Devices (HID). The basic HID handling is done in the kernel,
+	and HID reports can be sent/received through I/O on the
+	/dev/hidgX character devices.
+
+	For more details about HID, see the developer page on
+	http://www.usb.org/developers/hidpage/
+
+Configuration
+
+	g_hid is a platform driver, so to use it you need to add
+	struct platform_device(s) to your platform code defining the
+	HID function descriptors you want to use - E.G. something
+	like:
+
+#include <linux/platform_device.h>
+#include <linux/usb/g_hid.h>
+
+/* hid descriptor for a keyboard */
+static struct hidg_func_descriptor my_hid_data = {
+	.subclass		= 0, /* No subclass */
+	.protocol		= 1, /* Keyboard */
+	.report_length		= 8,
+	.report_desc_length	= 63,
+	.report_desc		= {
+		0x05, 0x01,	/* USAGE_PAGE (Generic Desktop)	          */
+		0x09, 0x06,	/* USAGE (Keyboard)                       */
+		0xa1, 0x01,	/* COLLECTION (Application)               */
+		0x05, 0x07,	/*   USAGE_PAGE (Keyboard)                */
+		0x19, 0xe0,	/*   USAGE_MINIMUM (Keyboard LeftControl) */
+		0x29, 0xe7,	/*   USAGE_MAXIMUM (Keyboard Right GUI)   */
+		0x15, 0x00,	/*   LOGICAL_MINIMUM (0)                  */
+		0x25, 0x01,	/*   LOGICAL_MAXIMUM (1)                  */
+		0x75, 0x01,	/*   REPORT_SIZE (1)                      */
+		0x95, 0x08,	/*   REPORT_COUNT (8)                     */
+		0x81, 0x02,	/*   INPUT (Data,Var,Abs)                 */
+		0x95, 0x01,	/*   REPORT_COUNT (1)                     */
+		0x75, 0x08,	/*   REPORT_SIZE (8)                      */
+		0x81, 0x03,	/*   INPUT (Cnst,Var,Abs)                 */
+		0x95, 0x05,	/*   REPORT_COUNT (5)                     */
+		0x75, 0x01,	/*   REPORT_SIZE (1)                      */
+		0x05, 0x08,	/*   USAGE_PAGE (LEDs)                    */
+		0x19, 0x01,	/*   USAGE_MINIMUM (Num Lock)             */
+		0x29, 0x05,	/*   USAGE_MAXIMUM (Kana)                 */
+		0x91, 0x02,	/*   OUTPUT (Data,Var,Abs)                */
+		0x95, 0x01,	/*   REPORT_COUNT (1)                     */
+		0x75, 0x03,	/*   REPORT_SIZE (3)                      */
+		0x91, 0x03,	/*   OUTPUT (Cnst,Var,Abs)                */
+		0x95, 0x06,	/*   REPORT_COUNT (6)                     */
+		0x75, 0x08,	/*   REPORT_SIZE (8)                      */
+		0x15, 0x00,	/*   LOGICAL_MINIMUM (0)                  */
+		0x25, 0x65,	/*   LOGICAL_MAXIMUM (101)                */
+		0x05, 0x07,	/*   USAGE_PAGE (Keyboard)                */
+		0x19, 0x00,	/*   USAGE_MINIMUM (Reserved)             */
+		0x29, 0x65,	/*   USAGE_MAXIMUM (Keyboard Application) */
+		0x81, 0x00,	/*   INPUT (Data,Ary,Abs)                 */
+		0xc0		/* END_COLLECTION                         */
+	}
+};
+
+static struct platform_device my_hid = {
+	.name			= "hidg",
+	.id			= 0,
+	.num_resources		= 0,
+	.resource		= 0,
+	.dev.platform_data	= &my_hid_data,
+};
+
+	You can add as many HID functions as you want, only limited by
+	the amount of interrupt endpoints your gadget driver supports.
+
+Send and receive HID reports
+
+	HID reports can be sent/received using read/write on the
+	/dev/hidgX character devices. See below for an example program
+	to do this.
+
+	hid_gadget_test is a small interactive program to test the HID
+ 	gadget driver. To use, point it at a hidg device and set the
+ 	device type (keyboard / mouse / joystick) - E.G.:
+
+		# hid_gadget_test /dev/hidg0 keyboard
+
+	You are now in the prompt of hid_gadget_test. You can type any
+	combination of options and values. Available options and
+	values are listed at program start. In keyboard mode you can
+	send up to six values.
+
+	For example type: g i s t r --left-shift
+
+	Hit return and the corresponding report will be sent by the
+	HID gadget.
+
+	Another interesting example is the caps lock test. Type
+	-–caps-lock and hit return. A report is then sent by the
+	gadget and you should receive the host answer, corresponding
+	to the caps lock LED status.
+
+		--caps-lock
+		recv report:2
+
+	With this command:
+
+		# hid_gadget_test /dev/hidg1 mouse
+
+	You can test the mouse emulation. Values are two signed numbers.
+
+
+Sample code
+
+/* hid_gadget_test */
+
+#include <pthread.h>
+#include <string.h>
+#include <stdio.h>
+#include <ctype.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+#define BUF_LEN 512
+
+struct options {
+	const char    *opt;
+	unsigned char val;
+};
+
+static struct options kmod[] = {
+	{.opt = "--left-ctrl",		.val = 0x01},
+	{.opt = "--right-ctrl",		.val = 0x10},
+	{.opt = "--left-shift",		.val = 0x02},
+	{.opt = "--right-shift",	.val = 0x20},
+	{.opt = "--left-alt",		.val = 0x04},
+	{.opt = "--right-alt",		.val = 0x40},
+	{.opt = "--left-meta",		.val = 0x08},
+	{.opt = "--right-meta",		.val = 0x80},
+	{.opt = NULL}
+};
+
+static struct options kval[] = {
+	{.opt = "--return",	.val = 0x28},
+	{.opt = "--esc",	.val = 0x29},
+	{.opt = "--bckspc",	.val = 0x2a},
+	{.opt = "--tab",	.val = 0x2b},
+	{.opt = "--spacebar",	.val = 0x2c},
+	{.opt = "--caps-lock",	.val = 0x39},
+	{.opt = "--f1",		.val = 0x3a},
+	{.opt = "--f2",		.val = 0x3b},
+	{.opt = "--f3",		.val = 0x3c},
+	{.opt = "--f4",		.val = 0x3d},
+	{.opt = "--f5",		.val = 0x3e},
+	{.opt = "--f6",		.val = 0x3f},
+	{.opt = "--f7",		.val = 0x40},
+	{.opt = "--f8",		.val = 0x41},
+	{.opt = "--f9",		.val = 0x42},
+	{.opt = "--f10",	.val = 0x43},
+	{.opt = "--f11",	.val = 0x44},
+	{.opt = "--f12",	.val = 0x45},
+	{.opt = "--insert",	.val = 0x49},
+	{.opt = "--home",	.val = 0x4a},
+	{.opt = "--pageup",	.val = 0x4b},
+	{.opt = "--del",	.val = 0x4c},
+	{.opt = "--end",	.val = 0x4d},
+	{.opt = "--pagedown",	.val = 0x4e},
+	{.opt = "--right",	.val = 0x4f},
+	{.opt = "--left",	.val = 0x50},
+	{.opt = "--down",	.val = 0x51},
+	{.opt = "--kp-enter",	.val = 0x58},
+	{.opt = "--up",		.val = 0x52},
+	{.opt = "--num-lock",	.val = 0x53},
+	{.opt = NULL}
+};
+
+int keyboard_fill_report(char report[8], char buf[BUF_LEN], int *hold)
+{
+	char *tok = strtok(buf, " ");
+	int key = 0;
+	int i = 0;
+
+	for (; tok != NULL; tok = strtok(NULL, " ")) {
+
+		if (strcmp(tok, "--quit") == 0)
+			return -1;
+
+		if (strcmp(tok, "--hold") == 0) {
+			*hold = 1;
+			continue;
+		}
+
+		if (key < 6) {
+			for (i = 0; kval[i].opt != NULL; i++)
+				if (strcmp(tok, kval[i].opt) == 0) {
+					report[2 + key++] = kval[i].val;
+					break;
+				}
+			if (kval[i].opt != NULL)
+				continue;
+		}
+
+		if (key < 6)
+			if (islower(tok[0])) {
+				report[2 + key++] = (tok[0] - ('a' - 0x04));
+				continue;
+			}
+
+		for (i = 0; kmod[i].opt != NULL; i++)
+			if (strcmp(tok, kmod[i].opt) == 0) {
+				report[0] = report[0] | kmod[i].val;
+				break;
+			}
+		if (kmod[i].opt != NULL)
+			continue;
+
+		if (key < 6)
+			fprintf(stderr, "unknown option: %s\n", tok);
+	}
+	return 8;
+}
+
+static struct options mmod[] = {
+	{.opt = "--b1", .val = 0x01},
+	{.opt = "--b2", .val = 0x02},
+	{.opt = "--b3", .val = 0x04},
+	{.opt = NULL}
+};
+
+int mouse_fill_report(char report[8], char buf[BUF_LEN], int *hold)
+{
+	char *tok = strtok(buf, " ");
+	int mvt = 0;
+	int i = 0;
+	for (; tok != NULL; tok = strtok(NULL, " ")) {
+
+		if (strcmp(tok, "--quit") == 0)
+			return -1;
+
+		if (strcmp(tok, "--hold") == 0) {
+			*hold = 1;
+			continue;
+		}
+
+		for (i = 0; mmod[i].opt != NULL; i++)
+			if (strcmp(tok, mmod[i].opt) == 0) {
+				report[0] = report[0] | mmod[i].val;
+				break;
+			}
+		if (mmod[i].opt != NULL)
+			continue;
+
+		if (!(tok[0] == '-' && tok[1] == '-') && mvt < 2) {
+			errno = 0;
+			report[1 + mvt++] = (char)strtol(tok, NULL, 0);
+			if (errno != 0) {
+				fprintf(stderr, "Bad value:'%s'\n", tok);
+				report[1 + mvt--] = 0;
+			}
+			continue;
+		}
+
+		fprintf(stderr, "unknown option: %s\n", tok);
+	}
+	return 3;
+}
+
+static struct options jmod[] = {
+	{.opt = "--b1",		.val = 0x10},
+	{.opt = "--b2",		.val = 0x20},
+	{.opt = "--b3",		.val = 0x40},
+	{.opt = "--b4",		.val = 0x80},
+	{.opt = "--hat1",	.val = 0x00},
+	{.opt = "--hat2",	.val = 0x01},
+	{.opt = "--hat3",	.val = 0x02},
+	{.opt = "--hat4",	.val = 0x03},
+	{.opt = "--hatneutral",	.val = 0x04},
+	{.opt = NULL}
+};
+
+int joystick_fill_report(char report[8], char buf[BUF_LEN], int *hold)
+{
+	char *tok = strtok(buf, " ");
+	int mvt = 0;
+	int i = 0;
+
+	*hold = 1;
+
+	/* set default hat position: neutral */
+	report[3] = 0x04;
+
+	for (; tok != NULL; tok = strtok(NULL, " ")) {
+
+		if (strcmp(tok, "--quit") == 0)
+			return -1;
+
+		for (i = 0; jmod[i].opt != NULL; i++)
+			if (strcmp(tok, jmod[i].opt) == 0) {
+				report[3] = (report[3] & 0xF0) | jmod[i].val;
+				break;
+			}
+		if (jmod[i].opt != NULL)
+			continue;
+
+		if (!(tok[0] == '-' && tok[1] == '-') && mvt < 3) {
+			errno = 0;
+			report[mvt++] = (char)strtol(tok, NULL, 0);
+			if (errno != 0) {
+				fprintf(stderr, "Bad value:'%s'\n", tok);
+				report[mvt--] = 0;
+			}
+			continue;
+		}
+
+		fprintf(stderr, "unknown option: %s\n", tok);
+	}
+	return 4;
+}
+
+void print_options(char c)
+{
+	int i = 0;
+
+	if (c == 'k') {
+		printf("	keyboard options:\n"
+		       "		--hold\n");
+		for (i = 0; kmod[i].opt != NULL; i++)
+			printf("\t\t%s\n", kmod[i].opt);
+		printf("\n	keyboard values:\n"
+		       "		[a-z] or\n");
+		for (i = 0; kval[i].opt != NULL; i++)
+			printf("\t\t%-8s%s", kval[i].opt, i % 2 ? "\n" : "");
+		printf("\n");
+	} else if (c == 'm') {
+		printf("	mouse options:\n"
+		       "		--hold\n");
+		for (i = 0; mmod[i].opt != NULL; i++)
+			printf("\t\t%s\n", mmod[i].opt);
+		printf("\n	mouse values:\n"
+		       "		Two signed numbers\n"
+		       "--quit to close\n");
+	} else {
+		printf("	joystick options:\n");
+		for (i = 0; jmod[i].opt != NULL; i++)
+			printf("\t\t%s\n", jmod[i].opt);
+		printf("\n	joystick values:\n"
+		       "		three signed numbers\n"
+		       "--quit to close\n");
+	}
+}
+
+int main(int argc, const char *argv[])
+{
+	const char *filename = NULL;
+	int fd = 0;
+	char buf[BUF_LEN];
+	int cmd_len;
+	char report[8];
+	int to_send = 8;
+	int hold = 0;
+	fd_set rfds;
+	int retval, i;
+
+	if (argc < 3) {
+		fprintf(stderr, "Usage: %s devname mouse|keyboard|joystick\n",
+			argv[0]);
+		return 1;
+	}
+
+	if (argv[2][0] != 'k' && argv[2][0] != 'm' && argv[2][0] != 'j')
+	  return 2;
+
+	filename = argv[1];
+
+	if ((fd = open(filename, O_RDWR, 0666)) == -1) {
+		perror(filename);
+		return 3;
+	}
+
+	print_options(argv[2][0]);
+
+	while (42) {
+
+		FD_ZERO(&rfds);
+		FD_SET(STDIN_FILENO, &rfds);
+		FD_SET(fd, &rfds);
+
+		retval = select(fd + 1, &rfds, NULL, NULL, NULL);
+		if (retval == -1 && errno == EINTR)
+			continue;
+		if (retval < 0) {
+			perror("select()");
+			return 4;
+		}
+
+		if (FD_ISSET(fd, &rfds)) {
+			cmd_len = read(fd, buf, BUF_LEN - 1);
+			printf("recv report:");
+			for (i = 0; i < cmd_len; i++)
+				printf(" %02x", buf[i]);
+			printf("\n");
+		}
+
+		if (FD_ISSET(STDIN_FILENO, &rfds)) {
+			memset(report, 0x0, sizeof(report));
+			cmd_len = read(STDIN_FILENO, buf, BUF_LEN - 1);
+
+			if (cmd_len == 0)
+				break;
+
+			buf[cmd_len - 1] = '\0';
+			hold = 0;
+
+			memset(report, 0x0, sizeof(report));
+			if (argv[2][0] == 'k')
+				to_send = keyboard_fill_report(report, buf, &hold);
+			else if (argv[2][0] == 'm')
+				to_send = mouse_fill_report(report, buf, &hold);
+			else
+				to_send = joystick_fill_report(report, buf, &hold);
+
+			if (to_send == -1)
+				break;
+
+			if (write(fd, report, to_send) != to_send) {
+				perror(filename);
+				return 5;
+			}
+			if (!hold) {
+				memset(report, 0x0, sizeof(report));
+				if (write(fd, report, to_send) != to_send) {
+					perror(filename);
+					return 6;
+				}
+			}
+		}
+	}
+
+	close(fd);
+	return 0;
+}

drivers/usb/gadget/Kconfig

@@ -863,6 +863,17 @@ config USB_G_MULTI_CDC
 
 	  If unsure, say "y".
 
+config USB_G_HID
+	tristate "HID Gadget"
+	help
+	  The HID gadget driver provides generic emulation of USB
+	  Human Interface Devices (HID).
+
+	  For more information, see Documentation/usb/gadget_hid.txt which
+	  includes sample code for accessing the device files.
+
+	  Say "y" to link the driver statically, or "m" to build a
+	  dynamically linked module called "g_hid".
 
 # put drivers that need isochronous transfer support (for audio
 # or video class gadget drivers), or specific hardware, here.

drivers/usb/gadget/Makefile

@@ -43,6 +43,7 @@ g_mass_storage-objs		:= mass_storage.o
 g_printer-objs			:= printer.o
 g_cdc-objs			:= cdc2.o
 g_multi-objs			:= multi.o
+g_hid-objs			:= hid.o
 g_nokia-objs			:= nokia.o
 
 obj-$(CONFIG_USB_ZERO)		+= g_zero.o
@@ -55,6 +56,7 @@ obj-$(CONFIG_USB_G_SERIAL)	+= g_serial.o
 obj-$(CONFIG_USB_G_PRINTER)	+= g_printer.o
 obj-$(CONFIG_USB_MIDI_GADGET)	+= g_midi.o
 obj-$(CONFIG_USB_CDC_COMPOSITE) += g_cdc.o
+obj-$(CONFIG_USB_G_HID)		+= g_hid.o
 obj-$(CONFIG_USB_G_MULTI)	+= g_multi.o
 obj-$(CONFIG_USB_G_NOKIA)	+= g_nokia.o
 

drivers/usb/gadget/f_hid.c

+/*
+ * f_hid.c -- USB HID function driver
+ *
+ * Copyright (C) 2010 Fabien Chouteau <fabien.chouteau@barco.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/kernel.h>
+#include <linux/utsname.h>
+#include <linux/module.h>
+#include <linux/hid.h>
+#include <linux/cdev.h>
+#include <linux/mutex.h>
+#include <linux/poll.h>
+#include <linux/smp_lock.h>
+#include <linux/uaccess.h>
+#include <linux/wait.h>
+#include <linux/usb/g_hid.h>
+
+static int major, minors;
+static struct class *hidg_class;
+
+/*-------------------------------------------------------------------------*/
+/*                            HID gadget struct                            */
+
+struct f_hidg {
+	/* configuration */
+	unsigned char			bInterfaceSubClass;
+	unsigned char			bInterfaceProtocol;
+	unsigned short			report_desc_length;
+	char				*report_desc;
+	unsigned short			report_length;
+
+	/* recv report */
+	char				*set_report_buff;
+	unsigned short			set_report_length;
+	spinlock_t			spinlock;
+	wait_queue_head_t		read_queue;
+
+	/* send report */
+	struct mutex			lock;
+	bool				write_pending;
+	wait_queue_head_t		write_queue;
+	struct usb_request		*req;
+
+	int				minor;
+	struct cdev			cdev;
+	struct usb_function		func;
+	struct usb_ep			*in_ep;
+	struct usb_endpoint_descriptor	*fs_in_ep_desc;
+	struct usb_endpoint_descriptor	*hs_in_ep_desc;
+};
+
+static inline struct f_hidg *func_to_hidg(struct usb_function *f)
+{
+	return container_of(f, struct f_hidg, func);
+}
+
+/*-------------------------------------------------------------------------*/
+/*                           Static descriptors                            */
+
+static struct usb_interface_descriptor hidg_interface_desc = {
+	.bLength		= sizeof hidg_interface_desc,
+	.bDescriptorType	= USB_DT_INTERFACE,
+	/* .bInterfaceNumber	= DYNAMIC */
+	.bAlternateSetting	= 0,
+	.bNumEndpoints		= 1,
+	.bInterfaceClass	= USB_CLASS_HID,
+	/* .bInterfaceSubClass	= DYNAMIC */
+	/* .bInterfaceProtocol	= DYNAMIC */
+	/* .iInterface		= DYNAMIC */
+};
+
+static struct hid_descriptor hidg_desc = {
+	.bLength			= sizeof hidg_desc,
+	.bDescriptorType		= HID_DT_HID,
+	.bcdHID				= 0x0101,
+	.bCountryCode			= 0x00,
+	.bNumDescriptors		= 0x1,
+	/*.desc[0].bDescriptorType	= DYNAMIC */
+	/*.desc[0].wDescriptorLenght	= DYNAMIC */
+};
+
+/* High-Speed Support */
+
+static struct usb_endpoint_descriptor hidg_hs_in_ep_desc = {
+	.bLength		= USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType	= USB_DT_ENDPOINT,
+	.bEndpointAddress	= USB_DIR_IN,
+	.bmAttributes		= USB_ENDPOINT_XFER_INT,
+	/*.wMaxPacketSize	= DYNAMIC */
+	.bInterval		= 4, /* FIXME: Add this field in the
+				      * HID gadget configuration?
+				      * (struct hidg_func_descriptor)
+				      */
+};
+
+static struct usb_descriptor_header *hidg_hs_descriptors[] = {
+	(struct usb_descriptor_header *)&hidg_interface_desc,
+	(struct usb_descriptor_header *)&hidg_desc,
+	(struct usb_descriptor_header *)&hidg_hs_in_ep_desc,
+	NULL,
+};
+
+/* Full-Speed Support */
+
+static struct usb_endpoint_descriptor hidg_fs_in_ep_desc = {
+	.bLength		= USB_DT_ENDPOINT_SIZE,
+	.bDescriptorType	= USB_DT_ENDPOINT,
+	.bEndpointAddress	= USB_DIR_IN,
+	.bmAttributes		= USB_ENDPOINT_XFER_INT,
+	/*.wMaxPacketSize	= DYNAMIC */
+	.bInterval		= 10, /* FIXME: Add this field in the
+				       * HID gadget configuration?
+				       * (struct hidg_func_descriptor)
+				       */
+};
+
+static struct usb_descriptor_header *hidg_fs_descriptors[] = {
+	(struct usb_descriptor_header *)&hidg_interface_desc,
+	(struct usb_descriptor_header *)&hidg_desc,
+	(struct usb_descriptor_header *)&hidg_fs_in_ep_desc,
+	NULL,
+};
+
+/*-------------------------------------------------------------------------*/
+/*                              Char Device                                */
+
+static ssize_t f_hidg_read(struct file *file, char __user *buffer,
+			size_t count, loff_t *ptr)
+{
+	struct f_hidg	*hidg     = (struct f_hidg *)file->private_data;
+	char		*tmp_buff = NULL;
+	unsigned long	flags;
+
+	if (!count)
+		return 0;
+
+	if (!access_ok(VERIFY_WRITE, buffer, count))
+		return -EFAULT;
+
+	spin_lock_irqsave(&hidg->spinlock, flags);
+
+#define READ_COND (hidg->set_report_buff != NULL)
+
+	while (!READ_COND) {
+		spin_unlock_irqrestore(&hidg->spinlock, flags);
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		if (wait_event_interruptible(hidg->read_queue, READ_COND))
+			return -ERESTARTSYS;
+
+		spin_lock_irqsave(&hidg->spinlock, flags);
+	}
+
+
+	count = min_t(unsigned, count, hidg->set_report_length);
+	tmp_buff = hidg->set_report_buff;
+	hidg->set_report_buff = NULL;
+
+	spin_unlock_irqrestore(&hidg->spinlock, flags);
+
+	if (tmp_buff != NULL) {
+		/* copy to user outside spinlock */
+		count -= copy_to_user(buffer, tmp_buff, count);
+		kfree(tmp_buff);
+	} else
+		count = -ENOMEM;
+
+	return count;
+}
+
+static void f_hidg_req_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_hidg *hidg = (struct f_hidg *)ep->driver_data;
+
+	if (req->status != 0) {
+		ERROR(hidg->func.config->cdev,
+			"End Point Request ERROR: %d\n", req->status);
+	}
+
+	hidg->write_pending = 0;
+	wake_up(&hidg->write_queue);
+}
+
+static ssize_t f_hidg_write(struct file *file, const char __user *buffer,
+			    size_t count, loff_t *offp)
+{
+	struct f_hidg *hidg  = (struct f_hidg *)file->private_data;
+	ssize_t status = -ENOMEM;
+
+	if (!access_ok(VERIFY_READ, buffer, count))
+		return -EFAULT;
+
+	mutex_lock(&hidg->lock);
+
+#define WRITE_COND (!hidg->write_pending)
+
+	/* write queue */
+	while (!WRITE_COND) {
+		mutex_unlock(&hidg->lock);
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		if (wait_event_interruptible_exclusive(
+				hidg->write_queue, WRITE_COND))
+			return -ERESTARTSYS;
+
+		mutex_lock(&hidg->lock);
+	}
+
+	count  = min_t(unsigned, count, hidg->report_length);
+	status = copy_from_user(hidg->req->buf, buffer, count);
+
+	if (status != 0) {
+		ERROR(hidg->func.config->cdev,
+			"copy_from_user error\n");
+		mutex_unlock(&hidg->lock);
+		return -EINVAL;
+	}
+
+	hidg->req->status   = 0;
+	hidg->req->zero     = 0;
+	hidg->req->length   = count;
+	hidg->req->complete = f_hidg_req_complete;
+	hidg->req->context  = hidg;
+	hidg->write_pending = 1;
+
+	status = usb_ep_queue(hidg->in_ep, hidg->req, GFP_ATOMIC);
+	if (status < 0) {
+		ERROR(hidg->func.config->cdev,
+			"usb_ep_queue error on int endpoint %zd\n", status);
+		hidg->write_pending = 0;
+		wake_up(&hidg->write_queue);
+	} else {
+		status = count;
+	}
+
+	mutex_unlock(&hidg->lock);
+
+	return status;
+}
+
+static unsigned int f_hidg_poll(struct file *file, poll_table *wait)
+{
+	struct f_hidg	*hidg  = (struct f_hidg *)file->private_data;
+	unsigned int	ret = 0;
+
+	poll_wait(file, &hidg->read_queue, wait);
+	poll_wait(file, &hidg->write_queue, wait);
+
+	if (WRITE_COND)
+		ret |= POLLOUT | POLLWRNORM;
+
+	if (READ_COND)
+		ret |= POLLIN | POLLRDNORM;
+
+	return ret;
+}
+
+#undef WRITE_COND
+#undef READ_COND
+
+static int f_hidg_release(struct inode *inode, struct file *fd)
+{
+	fd->private_data = NULL;
+	return 0;
+}
+
+static int f_hidg_open(struct inode *inode, struct file *fd)
+{
+	struct f_hidg *hidg =
+		container_of(inode->i_cdev, struct f_hidg, cdev);
+
+	fd->private_data = hidg;
+
+	return 0;
+}
+
+/*-------------------------------------------------------------------------*/
+/*                                usb_function                             */
+
+static void hidg_set_report_complete(struct usb_ep *ep, struct usb_request *req)
+{
+	struct f_hidg *hidg = (struct f_hidg *)req->context;
+
+	if (req->status != 0 || req->buf == NULL || req->actual == 0) {
+		ERROR(hidg->func.config->cdev, "%s FAILED\n", __func__);
+		return;
+	}
+
+	spin_lock(&hidg->spinlock);
+
+	hidg->set_report_buff = krealloc(hidg->set_report_buff,
+					 req->actual, GFP_ATOMIC);
+
+	if (hidg->set_report_buff == NULL) {
+		spin_unlock(&hidg->spinlock);
+		return;
+	}
+	hidg->set_report_length = req->actual;
+	memcpy(hidg->set_report_buff, req->buf, req->actual);
+
+	spin_unlock(&hidg->spinlock);
+
+	wake_up(&hidg->read_queue);
+
+	return;
+}
+
+static int hidg_setup(struct usb_function *f,
+		const struct usb_ctrlrequest *ctrl)
+{
+	struct f_hidg			*hidg = func_to_hidg(f);
+	struct usb_composite_dev	*cdev = f->config->cdev;
+	struct usb_request		*req  = cdev->req;
+	int status = 0;
+	__u16 value, length;
+
+	value	= __le16_to_cpu(ctrl->wValue);
+	length	= __le16_to_cpu(ctrl->wLength);
+
+	VDBG(cdev, "hid_setup crtl_request : bRequestType:0x%x bRequest:0x%x "
+		"Value:0x%x\n", ctrl->bRequestType, ctrl->bRequest, value);
+
+	switch ((ctrl->bRequestType << 8) | ctrl->bRequest) {
+	case ((USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
+		  | HID_REQ_GET_REPORT):
+		VDBG(cdev, "get_report\n");
+
+		/* send an empty report */
+		length = min_t(unsigned, length, hidg->report_length);
+		memset(req->buf, 0x0, length);
+
+		goto respond;
+		break;
+
+	case ((USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
+		  | HID_REQ_GET_PROTOCOL):
+		VDBG(cdev, "get_protocol\n");
+		goto stall;
+		break;
+
+	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
+		  | HID_REQ_SET_REPORT):
+		VDBG(cdev, "set_report | wLenght=%d\n", ctrl->wLength);
+		req->context  = hidg;
+		req->complete = hidg_set_report_complete;
+		goto respond;
+		break;
+
+	case ((USB_DIR_OUT | USB_TYPE_CLASS | USB_RECIP_INTERFACE) << 8
+		  | HID_REQ_SET_PROTOCOL):
+		VDBG(cdev, "set_protocol\n");
+		goto stall;
+		break;
+
+	case ((USB_DIR_IN | USB_TYPE_STANDARD | USB_RECIP_INTERFACE) << 8
+		  | USB_REQ_GET_DESCRIPTOR):
+		switch (value >> 8) {
+		case HID_DT_REPORT:
+			VDBG(cdev, "USB_REQ_GET_DESCRIPTOR: REPORT\n");
+			length = min_t(unsigned short, length,
+						   hidg->report_desc_length);
+			memcpy(req->buf, hidg->report_desc, length);
+			goto respond;
+			break;
+
+		default:
+			VDBG(cdev, "Unknown decriptor request 0x%x\n",
+				 value >> 8);
+			goto stall;
+			break;
+		}
+		break;
+
+	default:
+		VDBG(cdev, "Unknown request 0x%x\n",
+			 ctrl->bRequest);
+		goto stall;
+		break;
+	}
+
+stall:
+	return -EOPNOTSUPP;
+
+respond:
+	req->zero = 0;
+	req->length = length;
+	status = usb_ep_queue(cdev->gadget->ep0, req, GFP_ATOMIC);
+	if (status < 0)
+		ERROR(cdev, "usb_ep_queue error on ep0 %d\n", value);
+	return status;
+}
+
+static void hidg_disable(struct usb_function *f)
+{
+	struct f_hidg *hidg = func_to_hidg(f);
+
+	usb_ep_disable(hidg->in_ep);
+	hidg->in_ep->driver_data = NULL;
+
+	return;
+}
+
+static int hidg_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
+{
+	struct usb_composite_dev		*cdev = f->config->cdev;
+	struct f_hidg				*hidg = func_to_hidg(f);
+	const struct usb_endpoint_descriptor	*ep_desc;
+	int status = 0;
+
+	VDBG(cdev, "hidg_set_alt intf:%d alt:%d\n", intf, alt);
+
+	if (hidg->in_ep != NULL) {
+		/* restart endpoint */
+		if (hidg->in_ep->driver_data != NULL)
+			usb_ep_disable(hidg->in_ep);
+
+		ep_desc = ep_choose(f->config->cdev->gadget,
+				hidg->hs_in_ep_desc, hidg->fs_in_ep_desc);
+		status = usb_ep_enable(hidg->in_ep, ep_desc);
+		if (status < 0) {
+			ERROR(cdev, "Enable endpoint FAILED!\n");
+			goto fail;
+		}
+		hidg->in_ep->driver_data = hidg;
+	}
+fail:
+	return status;
+}
+
+const struct file_operations f_hidg_fops = {
+	.owner		= THIS_MODULE,
+	.open		= f_hidg_open,
+	.release	= f_hidg_release,
+	.write		= f_hidg_write,
+	.read		= f_hidg_read,
+	.poll		= f_hidg_poll,
+};
+
+static int __init hidg_bind(struct usb_configuration *c, struct usb_function *f)
+{
+	struct usb_ep		*ep;
+	struct f_hidg		*hidg = func_to_hidg(f);
+	int			status;
+	dev_t			dev;
+
+	/* allocate instance-specific interface IDs, and patch descriptors */
+	status = usb_interface_id(c, f);
+	if (status < 0)
+		goto fail;
+	hidg_interface_desc.bInterfaceNumber = status;
+
+
+	/* allocate instance-specific endpoints */
+	status = -ENODEV;
+	ep = usb_ep_autoconfig(c->cdev->gadget, &hidg_fs_in_ep_desc);
+	if (!ep)
+		goto fail;
+	ep->driver_data = c->cdev;	/* claim */
+	hidg->in_ep = ep;
+
+	/* preallocate request and buffer */
+	status = -ENOMEM;
+	hidg->req = usb_ep_alloc_request(hidg->in_ep, GFP_KERNEL);
+	if (!hidg->req)
+		goto fail;
+
+
+	hidg->req->buf = kmalloc(hidg->report_length, GFP_KERNEL);
+	if (!hidg->req->buf)
+		goto fail;
+
+	/* set descriptor dynamic values */
+	hidg_interface_desc.bInterfaceSubClass = hidg->bInterfaceSubClass;
+	hidg_interface_desc.bInterfaceProtocol = hidg->bInterfaceProtocol;
+	hidg_hs_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
+	hidg_fs_in_ep_desc.wMaxPacketSize = cpu_to_le16(hidg->report_length);
+	hidg_desc.desc[0].bDescriptorType = HID_DT_REPORT;
+	hidg_desc.desc[0].wDescriptorLength =
+		cpu_to_le16(hidg->report_desc_length);
+
+	hidg->set_report_buff = NULL;
+
+	/* copy descriptors */
+	f->descriptors = usb_copy_descriptors(hidg_fs_descriptors);
+	if (!f->descriptors)
+		goto fail;
+
+	hidg->fs_in_ep_desc = usb_find_endpoint(hidg_fs_descriptors,
+						f->descriptors,
+						&hidg_fs_in_ep_desc);
+
+	if (gadget_is_dualspeed(c->cdev->gadget)) {
+		hidg_hs_in_ep_desc.bEndpointAddress =
+			hidg_fs_in_ep_desc.bEndpointAddress;
+		f->hs_descriptors = usb_copy_descriptors(hidg_hs_descriptors);
+		if (!f->hs_descriptors)
+			goto fail;
+		hidg->hs_in_ep_desc = usb_find_endpoint(hidg_hs_descriptors,
+							f->hs_descriptors,
+							&hidg_hs_in_ep_desc);
+	} else {
+		hidg->hs_in_ep_desc = NULL;
+	}
+
+	mutex_init(&hidg->lock);
+	spin_lock_init(&hidg->spinlock);
+	init_waitqueue_head(&hidg->write_queue);
+	init_waitqueue_head(&hidg->read_queue);
+
+	/* create char device */
+	cdev_init(&hidg->cdev, &f_hidg_fops);
+	dev = MKDEV(major, hidg->minor);
+	status = cdev_add(&hidg->cdev, dev, 1);
+	if (status)
+		goto fail;
+
+	device_create(hidg_class, NULL, dev, NULL, "%s%d", "hidg", hidg->minor);
+
+	return 0;
+
+fail:
+	ERROR(f->config->cdev, "hidg_bind FAILED\n");
+	if (hidg->req != NULL) {
+		kfree(hidg->req->buf);
+		if (hidg->in_ep != NULL)
+			usb_ep_free_request(hidg->in_ep, hidg->req);
+	}
+
+	usb_free_descriptors(f->hs_descriptors);
+	usb_free_descriptors(f->descriptors);
+
+	return status;
+}
+
+static void hidg_unbind(struct usb_configuration *c, struct usb_function *f)
+{
+	struct f_hidg *hidg = func_to_hidg(f);
+
+	device_destroy(hidg_class, MKDEV(major, hidg->minor));
+	cdev_del(&hidg->cdev);
+
+	/* disable/free request and end point */
+	usb_ep_disable(hidg->in_ep);
+	usb_ep_dequeue(hidg->in_ep, hidg->req);
+	kfree(hidg->req->buf);
+	usb_ep_free_request(hidg->in_ep, hidg->req);
+
+	/* free descriptors copies */
+	usb_free_descriptors(f->hs_descriptors);
+	usb_free_descriptors(f->descriptors);
+
+	kfree(hidg->report_desc);
+	kfree(hidg->set_report_buff);
+	kfree(hidg);
+}
+
+/*-------------------------------------------------------------------------*/
+/*                                 Strings                                 */
+
+#define CT_FUNC_HID_IDX	0
+
+static struct usb_string ct_func_string_defs[] = {
+	[CT_FUNC_HID_IDX].s	= "HID Interface",
+	{},			/* end of list */
+};
+
+static struct usb_gadget_strings ct_func_string_table = {
+	.language	= 0x0409,	/* en-US */
+	.strings	= ct_func_string_defs,
+};
+
+static struct usb_gadget_strings *ct_func_strings[] = {
+	&ct_func_string_table,
+	NULL,
+};
+
+/*-------------------------------------------------------------------------*/
+/*                             usb_configuration                           */
+
+int __init hidg_bind_config(struct usb_configuration *c,
+			    struct hidg_func_descriptor *fdesc, int index)
+{
+	struct f_hidg *hidg;
+	int status;
+
+	if (index >= minors)
+		return -ENOENT;
+
+	/* maybe allocate device-global string IDs, and patch descriptors */
+	if (ct_func_string_defs[CT_FUNC_HID_IDX].id == 0) {
+		status = usb_string_id(c->cdev);
+		if (status < 0)
+			return status;
+		ct_func_string_defs[CT_FUNC_HID_IDX].id = status;
+		hidg_interface_desc.iInterface = status;
+	}
+
+	/* allocate and initialize one new instance */
+	hidg = kzalloc(sizeof *hidg, GFP_KERNEL);
+	if (!hidg)
+		return -ENOMEM;
+
+	hidg->minor = index;
+	hidg->bInterfaceSubClass = fdesc->subclass;
+	hidg->bInterfaceProtocol = fdesc->protocol;
+	hidg->report_length = fdesc->report_length;
+	hidg->report_desc_length = fdesc->report_desc_length;
+	hidg->report_desc = kmemdup(fdesc->report_desc,
+				    fdesc->report_desc_length,
+				    GFP_KERNEL);
+	if (!hidg->report_desc) {
+		kfree(hidg);
+		return -ENOMEM;
+	}
+
+	hidg->func.name    = "hid";
+	hidg->func.strings = ct_func_strings;
+	hidg->func.bind    = hidg_bind;
+	hidg->func.unbind  = hidg_unbind;
+	hidg->func.set_alt = hidg_set_alt;
+	hidg->func.disable = hidg_disable;
+	hidg->func.setup   = hidg_setup;
+
+	status = usb_add_function(c, &hidg->func);
+	if (status)
+		kfree(hidg);
+
+	return status;
+}
+
+int __init ghid_setup(struct usb_gadget *g, int count)
+{
+	int status;
+	dev_t dev;
+
+	hidg_class = class_create(THIS_MODULE, "hidg");
+
+	status = alloc_chrdev_region(&dev, 0, count, "hidg");
+	if (!status) {
+		major = MAJOR(dev);
+		minors = count;
+	}
+
+	return status;
+}
+
+void ghid_cleanup(void)
+{
+	if (major) {
+		unregister_chrdev_region(MKDEV(major, 0), minors);
+		major = minors = 0;
+	}
+
+	class_destroy(hidg_class);
+	hidg_class = NULL;
+}

drivers/usb/gadget/hid.c

+/*
+ * hid.c -- HID Composite driver
+ *
+ * Based on multi.c
+ *
+ * Copyright (C) 2010 Fabien Chouteau <fabien.chouteau@barco.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+
+#define DRIVER_DESC		"HID Gadget"
+#define DRIVER_VERSION		"2010/03/16"
+
+/*-------------------------------------------------------------------------*/
+
+#define HIDG_VENDOR_NUM		0x0525	/* XXX NetChip */
+#define HIDG_PRODUCT_NUM	0xa4ac	/* Linux-USB HID gadget */
+
+/*-------------------------------------------------------------------------*/
+
+/*
+ * kbuild is not very cooperative with respect to linking separately
+ * compiled library objects into one module.  So for now we won't use
+ * separate compilation ... ensuring init/exit sections work to shrink
+ * the runtime footprint, and giving us at least some parts of what
+ * a "gcc --combine ... part1.c part2.c part3.c ... " build would.
+ */
+
+#include "composite.c"
+#include "usbstring.c"
+#include "config.c"
+#include "epautoconf.c"
+
+#include "f_hid.c"
+
+
+struct hidg_func_node {
+	struct list_head node;
+	struct hidg_func_descriptor *func;
+};
+
+static LIST_HEAD(hidg_func_list);
+
+/*-------------------------------------------------------------------------*/
+
+static struct usb_device_descriptor device_desc = {
+	.bLength =		sizeof device_desc,
+	.bDescriptorType =	USB_DT_DEVICE,
+
+	.bcdUSB =		cpu_to_le16(0x0200),
+
+	/* .bDeviceClass =		USB_CLASS_COMM, */
+	/* .bDeviceSubClass =	0, */
+	/* .bDeviceProtocol =	0, */
+	.bDeviceClass =		0xEF,
+	.bDeviceSubClass =	2,
+	.bDeviceProtocol =	1,
+	/* .bMaxPacketSize0 = f(hardware) */
+
+	/* Vendor and product id can be overridden by module parameters.  */
+	.idVendor =		cpu_to_le16(HIDG_VENDOR_NUM),
+	.idProduct =		cpu_to_le16(HIDG_PRODUCT_NUM),
+	/* .bcdDevice = f(hardware) */
+	/* .iManufacturer = DYNAMIC */
+	/* .iProduct = DYNAMIC */
+	/* NO SERIAL NUMBER */
+	.bNumConfigurations =	1,
+};
+
+static struct usb_otg_descriptor otg_descriptor = {
+	.bLength =		sizeof otg_descriptor,
+	.bDescriptorType =	USB_DT_OTG,
+
+	/* REVISIT SRP-only hardware is possible, although
+	 * it would not be called "OTG" ...
+	 */
+	.bmAttributes =		USB_OTG_SRP | USB_OTG_HNP,
+};
+
+static const struct usb_descriptor_header *otg_desc[] = {
+	(struct usb_descriptor_header *) &otg_descriptor,
+	NULL,
+};
+
+
+/* string IDs are assigned dynamically */
+
+#define STRING_MANUFACTURER_IDX		0
+#define STRING_PRODUCT_IDX		1
+
+static char manufacturer[50];
+
+static struct usb_string strings_dev[] = {
+	[STRING_MANUFACTURER_IDX].s = manufacturer,
+	[STRING_PRODUCT_IDX].s = DRIVER_DESC,
+	{  } /* end of list */
+};
+
+static struct usb_gadget_strings stringtab_dev = {
+	.language	= 0x0409,	/* en-us */
+	.strings	= strings_dev,
+};
+
+static struct usb_gadget_strings *dev_strings[] = {
+	&stringtab_dev,
+	NULL,
+};
+
+
+
+/****************************** Configurations ******************************/
+
+static int __init do_config(struct usb_configuration *c)
+{
+	struct hidg_func_node *e;
+	int func = 0, status = 0;
+
+	if (gadget_is_otg(c->cdev->gadget)) {
+		c->descriptors = otg_desc;
+		c->bmAttributes |= USB_CONFIG_ATT_WAKEUP;
+	}
+
+	list_for_each_entry(e, &hidg_func_list, node) {
+		status = hidg_bind_config(c, e->func, func++);
+		if (status)
+			break;
+	}
+
+	return status;
+}
+
+static struct usb_configuration config_driver = {
+	.label			= "HID Gadget",
+	.bind			= do_config,
+	.bConfigurationValue	= 1,
+	/* .iConfiguration = DYNAMIC */
+	.bmAttributes		= USB_CONFIG_ATT_SELFPOWER,
+};
+
+/****************************** Gadget Bind ******************************/
+
+static int __init hid_bind(struct usb_composite_dev *cdev)
+{
+	struct usb_gadget *gadget = cdev->gadget;
+	struct list_head *tmp;
+	int status, gcnum, funcs = 0;
+
+	list_for_each(tmp, &hidg_func_list)
+		funcs++;
+
+	if (!funcs)
+		return -ENODEV;
+
+	/* set up HID */
+	status = ghid_setup(cdev->gadget, funcs);
+	if (status < 0)
+		return status;
+
+	gcnum = usb_gadget_controller_number(gadget);
+	if (gcnum >= 0)
+		device_desc.bcdDevice = cpu_to_le16(0x0300 | gcnum);
+	else
+		device_desc.bcdDevice = cpu_to_le16(0x0300 | 0x0099);
+
+
+	/* Allocate string descriptor numbers ... note that string
+	 * contents can be overridden by the composite_dev glue.
+	 */
+
+	/* device descriptor strings: manufacturer, product */
+	snprintf(manufacturer, sizeof manufacturer, "%s %s with %s",
+		init_utsname()->sysname, init_utsname()->release,
+		gadget->name);
+	status = usb_string_id(cdev);
+	if (status < 0)
+		return status;
+	strings_dev[STRING_MANUFACTURER_IDX].id = status;
+	device_desc.iManufacturer = status;
+
+	status = usb_string_id(cdev);
+	if (status < 0)
+		return status;
+	strings_dev[STRING_PRODUCT_IDX].id = status;
+	device_desc.iProduct = status;
+
+	/* register our configuration */
+	status = usb_add_config(cdev, &config_driver);
+	if (status < 0)
+		return status;
+
+	dev_info(&gadget->dev, DRIVER_DESC ", version: " DRIVER_VERSION "\n");
+
+	return 0;
+}
+
+static int __exit hid_unbind(struct usb_composite_dev *cdev)
+{
+	ghid_cleanup();
+	return 0;
+}
+
+static int __init hidg_plat_driver_probe(struct platform_device *pdev)
+{
+	struct hidg_func_descriptor *func = pdev->dev.platform_data;
+	struct hidg_func_node *entry;
+
+	if (!func) {
+		dev_err(&pdev->dev, "Platform data missing\n");
+		return -ENODEV;
+	}
+
+	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+	if (!entry)
+		return -ENOMEM;
+
+	entry->func = func;
+	list_add_tail(&entry->node, &hidg_func_list);
+
+	return 0;
+}
+
+static int __devexit hidg_plat_driver_remove(struct platform_device *pdev)
+{
+	struct hidg_func_node *e, *n;
+
+	list_for_each_entry_safe(e, n, &hidg_func_list, node) {
+		list_del(&e->node);
+		kfree(e);
+	}
+
+	return 0;
+}
+
+
+/****************************** Some noise ******************************/
+
+
+static struct usb_composite_driver hidg_driver = {
+	.name		= "g_hid",
+	.dev		= &device_desc,
+	.strings	= dev_strings,
+	.bind		= hid_bind,
+	.unbind		= __exit_p(hid_unbind),
+};
+
+static struct platform_driver hidg_plat_driver = {
+	.remove		= __devexit_p(hidg_plat_driver_remove),
+	.driver		= {
+		.owner	= THIS_MODULE,
+		.name	= "hidg",
+	},
+};
+
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_AUTHOR("Fabien Chouteau, Peter Korsgaard");
+MODULE_LICENSE("GPL");
+
+static int __init hidg_init(void)
+{
+	platform_driver_probe(&hidg_plat_driver, hidg_plat_driver_probe);
+	return usb_composite_register(&hidg_driver);
+}
+module_init(hidg_init);
+
+static void __exit hidg_cleanup(void)
+{
+	platform_driver_unregister(&hidg_plat_driver);
+	usb_composite_unregister(&hidg_driver);
+}
+module_exit(hidg_cleanup);

include/linux/usb/g_hid.h

+/*
+ * g_hid.h -- Header file for USB HID gadget driver
+ *
+ * Copyright (C) 2010 Fabien Chouteau <fabien.chouteau@barco.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#ifndef __LINUX_USB_G_HID_H
+#define __LINUX_USB_G_HID_H
+
+struct hidg_func_descriptor {
+	unsigned char		subclass;
+	unsigned char		protocol;
+	unsigned short		report_length;
+	unsigned short		report_desc_length;
+	unsigned char		report_desc[];
+};
+
+#endif /* __LINUX_USB_G_HID_H */