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;
}