serial.c

linux 内核源代码

/*
 * g_serial.c -- USB gadget serial driver
 *
 * Copyright 2003 (C) Al Borchers ([e-mail])
 *
 * This code is based in part on the Gadget Zero driver, which
 * is Copyright (C) 2003 by David Brownell, all rights reserved.
 *
 * This code also borrows from usbserial.c, which is
 * Copyright (C) 1999 - 2002 Greg Kroah-Hartman ([e-mail])
 * Copyright (C) 2000 Peter Berger ([e-mail])
 * Copyright (C) 2000 Al Borchers ([e-mail])
 *
 * This software is distributed under the terms of the GNU General
 * Public License ("GPL") as published by the Free Software Foundation,
 * either version 2 of that License or (at your option) any later version.
 *
 */

#include <linux/kernel.h>
#include <linux/utsname.h>
#include <linux/device.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>

#include <linux/usb/ch9.h>
#include <linux/usb/cdc.h>
#include <linux/usb/gadget.h>

#include "gadget_chips.h"


/* Defines */

#define GS_VERSION_STR			"v2.2"
#define GS_VERSION_NUM			0x0202

#define GS_LONG_NAME			"Gadget Serial"
#define GS_SHORT_NAME			"g_serial"

#define GS_MAJOR			127
#define GS_MINOR_START			0

#define GS_NUM_PORTS			16

#define GS_NUM_CONFIGS			1
#define GS_NO_CONFIG_ID			0
#define GS_BULK_CONFIG_ID		1
#define GS_ACM_CONFIG_ID		2

#define GS_MAX_NUM_INTERFACES		2
#define GS_BULK_INTERFACE_ID		0
#define GS_CONTROL_INTERFACE_ID		0
#define GS_DATA_INTERFACE_ID		1

#define GS_MAX_DESC_LEN			256

#define GS_DEFAULT_READ_Q_SIZE		32
#define GS_DEFAULT_WRITE_Q_SIZE		32

#define GS_DEFAULT_WRITE_BUF_SIZE	8192
#define GS_TMP_BUF_SIZE			8192

#define GS_CLOSE_TIMEOUT		15

#define GS_DEFAULT_USE_ACM		0

#define GS_DEFAULT_DTE_RATE		9600
#define GS_DEFAULT_DATA_BITS		8
#define GS_DEFAULT_PARITY		USB_CDC_NO_PARITY
#define GS_DEFAULT_CHAR_FORMAT		USB_CDC_1_STOP_BITS

/* maxpacket and other transfer characteristics vary by speed. */
static inline struct usb_endpoint_descriptor *
choose_ep_desc(struct usb_gadget *g, struct usb_endpoint_descriptor *hs,
		struct usb_endpoint_descriptor *fs)
{
	if (gadget_is_dualspeed(g) && g->speed == USB_SPEED_HIGH)
		return hs;
	return fs;
}


/* debug settings */
#ifdef DEBUG
static int debug = 1;
#else
#define	debug 0
#endif

#define gs_debug(format, arg...) \
	do { if (debug) printk(KERN_DEBUG format, ## arg); } while(0)
#define gs_debug_level(level, format, arg...) \
	do { if (debug>=level) printk(KERN_DEBUG format, ## arg); } while(0)


/* Thanks to NetChip Technologies for donating this product ID.
 *
 * DO NOT REUSE THESE IDs with a protocol-incompatible driver!!  Ever!!
 * Instead:  allocate your own, using normal USB-IF procedures.
 */
#define GS_VENDOR_ID			0x0525	/* NetChip */
#define GS_PRODUCT_ID			0xa4a6	/* Linux-USB Serial Gadget */
#define GS_CDC_PRODUCT_ID		0xa4a7	/* ... as CDC-ACM */

#define GS_LOG2_NOTIFY_INTERVAL		5	/* 1 << 5 == 32 msec */
#define GS_NOTIFY_MAXPACKET		8


/* Structures */

struct gs_dev;

/* circular buffer */
struct gs_buf {
	unsigned int		buf_size;
	char			*buf_buf;
	char			*buf_get;
	char			*buf_put;
};

/* list of requests */
struct gs_req_entry {
	struct list_head	re_entry;
	struct usb_request	*re_req;
};

/* the port structure holds info for each port, one for each minor number */
struct gs_port {
	struct gs_dev		*port_dev;	/* pointer to device struct */
	struct tty_struct	*port_tty;	/* pointer to tty struct */
	spinlock_t		port_lock;
	int			port_num;
	int			port_open_count;
	int			port_in_use;	/* open/close in progress */
	wait_queue_head_t	port_write_wait;/* waiting to write */
	struct gs_buf		*port_write_buf;
	struct usb_cdc_line_coding	port_line_coding;
};

/* the device structure holds info for the USB device */
struct gs_dev {
	struct usb_gadget	*dev_gadget;	/* gadget device pointer */
	spinlock_t		dev_lock;	/* lock for set/reset config */
	int			dev_config;	/* configuration number */
	struct usb_ep		*dev_notify_ep;	/* address of notify endpoint */
	struct usb_ep		*dev_in_ep;	/* address of in endpoint */
	struct usb_ep		*dev_out_ep;	/* address of out endpoint */
	struct usb_endpoint_descriptor		/* descriptor of notify ep */
				*dev_notify_ep_desc;
	struct usb_endpoint_descriptor		/* descriptor of in endpoint */
				*dev_in_ep_desc;
	struct usb_endpoint_descriptor		/* descriptor of out endpoint */
				*dev_out_ep_desc;
	struct usb_request	*dev_ctrl_req;	/* control request */
	struct list_head	dev_req_list;	/* list of write requests */
	int			dev_sched_port;	/* round robin port scheduled */
	struct gs_port		*dev_port[GS_NUM_PORTS]; /* the ports */
};


/* Functions */

/* module */
static int __init gs_module_init(void);
static void __exit gs_module_exit(void);

/* tty driver */
static int gs_open(struct tty_struct *tty, struct file *file);
static void gs_close(struct tty_struct *tty, struct file *file);
static int gs_write(struct tty_struct *tty,
	const unsigned char *buf, int count);
static void gs_put_char(struct tty_struct *tty, unsigned char ch);
static void gs_flush_chars(struct tty_struct *tty);
static int gs_write_room(struct tty_struct *tty);
static int gs_chars_in_buffer(struct tty_struct *tty);
static void gs_throttle(struct tty_struct * tty);
static void gs_unthrottle(struct tty_struct * tty);
static void gs_break(struct tty_struct *tty, int break_state);
static int  gs_ioctl(struct tty_struct *tty, struct file *file,
	unsigned int cmd, unsigned long arg);
static void gs_set_termios(struct tty_struct *tty, struct ktermios *old);

static int gs_send(struct gs_dev *dev);
static int gs_send_packet(struct gs_dev *dev, char *packet,
	unsigned int size);
static int gs_recv_packet(struct gs_dev *dev, char *packet,
	unsigned int size);
static void gs_read_complete(struct usb_ep *ep, struct usb_request *req);
static void gs_write_complete(struct usb_ep *ep, struct usb_request *req);

/* gadget driver */
static int gs_bind(struct usb_gadget *gadget);
static void gs_unbind(struct usb_gadget *gadget);
static int gs_setup(struct usb_gadget *gadget,
	const struct usb_ctrlrequest *ctrl);
static int gs_setup_standard(struct usb_gadget *gadget,
	const struct usb_ctrlrequest *ctrl);
static int gs_setup_class(struct usb_gadget *gadget,
	const struct usb_ctrlrequest *ctrl);
static void gs_setup_complete(struct usb_ep *ep, struct usb_request *req);
static void gs_disconnect(struct usb_gadget *gadget);
static int gs_set_config(struct gs_dev *dev, unsigned config);
static void gs_reset_config(struct gs_dev *dev);
static int gs_build_config_buf(u8 *buf, struct usb_gadget *g,
		u8 type, unsigned int index, int is_otg);

static struct usb_request *gs_alloc_req(struct usb_ep *ep, unsigned int len,
	gfp_t kmalloc_flags);
static void gs_free_req(struct usb_ep *ep, struct usb_request *req);

static struct gs_req_entry *gs_alloc_req_entry(struct usb_ep *ep, unsigned len,
	gfp_t kmalloc_flags);
static void gs_free_req_entry(struct usb_ep *ep, struct gs_req_entry *req);

static int gs_alloc_ports(struct gs_dev *dev, gfp_t kmalloc_flags);
static void gs_free_ports(struct gs_dev *dev);

/* circular buffer */
static struct gs_buf *gs_buf_alloc(unsigned int size, gfp_t kmalloc_flags);
static void gs_buf_free(struct gs_buf *gb);
static void gs_buf_clear(struct gs_buf *gb);
static unsigned int gs_buf_data_avail(struct gs_buf *gb);
static unsigned int gs_buf_space_avail(struct gs_buf *gb);
static unsigned int gs_buf_put(struct gs_buf *gb, const char *buf,
	unsigned int count);
static unsigned int gs_buf_get(struct gs_buf *gb, char *buf,
	unsigned int count);

/* external functions */
extern int net2280_set_fifo_mode(struct usb_gadget *gadget, int mode);


/* Globals */

static struct gs_dev *gs_device;

static const char *EP_IN_NAME;
static const char *EP_OUT_NAME;
static const char *EP_NOTIFY_NAME;

static struct mutex gs_open_close_lock[GS_NUM_PORTS];

static unsigned int read_q_size = GS_DEFAULT_READ_Q_SIZE;
static unsigned int write_q_size = GS_DEFAULT_WRITE_Q_SIZE;

static unsigned int write_buf_size = GS_DEFAULT_WRITE_BUF_SIZE;

static unsigned int use_acm = GS_DEFAULT_USE_ACM;


/* tty driver struct */
static const struct tty_operations gs_tty_ops = {
	.open =			gs_open,
	.close =		gs_close,
	.write =		gs_write,
	.put_char =		gs_put_char,
	.flush_chars =		gs_flush_chars,
	.write_room =		gs_write_room,
	.ioctl =		gs_ioctl,
	.set_termios =		gs_set_termios,
	.throttle =		gs_throttle,
	.unthrottle =		gs_unthrottle,
	.break_ctl =		gs_break,
	.chars_in_buffer =	gs_chars_in_buffer,
};
static struct tty_driver *gs_tty_driver;

/* gadget driver struct */
static struct usb_gadget_driver gs_gadget_driver = {
#ifdef CONFIG_USB_GADGET_DUALSPEED
	.speed =		USB_SPEED_HIGH,
#else
	.speed =		USB_SPEED_FULL,
#endif /* CONFIG_USB_GADGET_DUALSPEED */
	.function =		GS_LONG_NAME,
	.bind =			gs_bind,
	.unbind =		gs_unbind,
	.setup =		gs_setup,
	.disconnect =		gs_disconnect,
	.driver = {
		.name =		GS_SHORT_NAME,
	},
};


/* USB descriptors */

#define GS_MANUFACTURER_STR_ID	1
#define GS_PRODUCT_STR_ID	2
#define GS_SERIAL_STR_ID	3
#define GS_BULK_CONFIG_STR_ID	4
#define GS_ACM_CONFIG_STR_ID	5
#define GS_CONTROL_STR_ID	6
#define GS_DATA_STR_ID		7

/* static strings, in UTF-8 */
static char manufacturer[50];
static struct usb_string gs_strings[] = {
	{ GS_MANUFACTURER_STR_ID, manufacturer },
	{ GS_PRODUCT_STR_ID, GS_LONG_NAME },
	{ GS_SERIAL_STR_ID, "0" },
	{ GS_BULK_CONFIG_STR_ID, "Gadget Serial Bulk" },
	{ GS_ACM_CONFIG_STR_ID, "Gadget Serial CDC ACM" },
	{ GS_CONTROL_STR_ID, "Gadget Serial Control" },
	{ GS_DATA_STR_ID, "Gadget Serial Data" },
	{  } /* end of list */
};

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

static struct usb_device_descriptor gs_device_desc = {
	.bLength =		USB_DT_DEVICE_SIZE,
	.bDescriptorType =	USB_DT_DEVICE,
	.bcdUSB =		__constant_cpu_to_le16(0x0200),
	.bDeviceSubClass =	0,
	.bDeviceProtocol =	0,
	.idVendor =		__constant_cpu_to_le16(GS_VENDOR_ID),
	.idProduct =		__constant_cpu_to_le16(GS_PRODUCT_ID),
	.iManufacturer =	GS_MANUFACTURER_STR_ID,
	.iProduct =		GS_PRODUCT_STR_ID,
	.iSerialNumber =	GS_SERIAL_STR_ID,
	.bNumConfigurations =	GS_NUM_CONFIGS,
};

static struct usb_otg_descriptor gs_otg_descriptor = {
	.bLength =		sizeof(gs_otg_descriptor),
	.bDescriptorType =	USB_DT_OTG,
	.bmAttributes =		USB_OTG_SRP,
};

static struct usb_config_descriptor gs_bulk_config_desc = {
	.bLength =		USB_DT_CONFIG_SIZE,
	.bDescriptorType =	USB_DT_CONFIG,
	/* .wTotalLength computed dynamically */
	.bNumInterfaces =	1,
	.bConfigurationValue =	GS_BULK_CONFIG_ID,
	.iConfiguration =	GS_BULK_CONFIG_STR_ID,
	.bmAttributes =		USB_CONFIG_ATT_ONE | USB_CONFIG_ATT_SELFPOWER,
	.bMaxPower =		1,
};

static struct usb_config_descriptor gs_acm_config_desc = {
	.bLength =		USB_DT_CONFIG_SIZE,
	.bDescriptorType =	USB_DT_CONFIG,
	/* .wTotalLength computed dynamically */
	.bNumInterfaces =	2,
	.bConfigurationValue =	GS_ACM_CONFIG_ID,
	.iConfiguration =	GS_ACM_CONFIG_STR_ID,
	.bmAttributes =		USB_CONFIG_ATT_ONE | USB_CONFIG_ATT_SELFPOWER,
	.bMaxPower =		1,
};

static const struct usb_interface_descriptor gs_bulk_interface_desc = {
	.bLength =		USB_DT_INTERFACE_SIZE,
	.bDescriptorType =	USB_DT_INTERFACE,
	.bInterfaceNumber =	GS_BULK_INTERFACE_ID,
	.bNumEndpoints =	2,
	.bInterfaceClass =	USB_CLASS_CDC_DATA,
	.bInterfaceSubClass =	0,
	.bInterfaceProtocol =	0,
	.iInterface =		GS_DATA_STR_ID,
};

static const struct usb_interface_descriptor gs_control_interface_desc = {
	.bLength =		USB_DT_INTERFACE_SIZE,
	.bDescriptorType =	USB_DT_INTERFACE,
	.bInterfaceNumber =	GS_CONTROL_INTERFACE_ID,
	.bNumEndpoints =	1,
	.bInterfaceClass =	USB_CLASS_COMM,
	.bInterfaceSubClass =	USB_CDC_SUBCLASS_ACM,
	.bInterfaceProtocol =	USB_CDC_ACM_PROTO_AT_V25TER,
	.iInterface =		GS_CONTROL_STR_ID,
};

static const struct usb_interface_descriptor gs_data_interface_desc = {
	.bLength =		USB_DT_INTERFACE_SIZE,
	.bDescriptorType =	USB_DT_INTERFACE,
	.bInterfaceNumber =	GS_DATA_INTERFACE_ID,
	.bNumEndpoints =	2,
	.bInterfaceClass =	USB_CLASS_CDC_DATA,
	.bInterfaceSubClass =	0,
	.bInterfaceProtocol =	0,
	.iInterface =		GS_DATA_STR_ID,
};

static const struct usb_cdc_header_desc gs_header_desc = {
	.bLength =		sizeof(gs_header_desc),
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubType =	USB_CDC_HEADER_TYPE,
	.bcdCDC =		__constant_cpu_to_le16(0x0110),
};

static const struct usb_cdc_call_mgmt_descriptor gs_call_mgmt_descriptor = {
	.bLength =		sizeof(gs_call_mgmt_descriptor),
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubType =	USB_CDC_CALL_MANAGEMENT_TYPE,
	.bmCapabilities =	0,
	.bDataInterface =	1,	/* index of data interface */
};

static struct usb_cdc_acm_descriptor gs_acm_descriptor = {
	.bLength =		sizeof(gs_acm_descriptor),
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubType =	USB_CDC_ACM_TYPE,
	.bmCapabilities =	0,
};

static const struct usb_cdc_union_desc gs_union_desc = {
	.bLength =		sizeof(gs_union_desc),
	.bDescriptorType =	USB_DT_CS_INTERFACE,
	.bDescriptorSubType =	USB_CDC_UNION_TYPE,
	.bMasterInterface0 =	0,	/* index of control interface */
	.bSlaveInterface0 =	1,	/* index of data interface */
};

static struct usb_endpoint_descriptor gs_fullspeed_notify_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_IN,
	.bmAttributes =		USB_ENDPOINT_XFER_INT,
	.wMaxPacketSize =	__constant_cpu_to_le16(GS_NOTIFY_MAXPACKET),
	.bInterval =		1 << GS_LOG2_NOTIFY_INTERVAL,
};

static struct usb_endpoint_descriptor gs_fullspeed_in_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_IN,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
};

static struct usb_endpoint_descriptor gs_fullspeed_out_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_OUT,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
};

static const struct usb_descriptor_header *gs_bulk_fullspeed_function[] = {
	(struct usb_descriptor_header *) &gs_otg_descriptor,
	(struct usb_descriptor_header *) &gs_bulk_interface_desc,
	(struct usb_descriptor_header *) &gs_fullspeed_in_desc,
	(struct usb_descriptor_header *) &gs_fullspeed_out_desc,
	NULL,
};

static const struct usb_descriptor_header *gs_acm_fullspeed_function[] = {
	(struct usb_descriptor_header *) &gs_otg_descriptor,
	(struct usb_descriptor_header *) &gs_control_interface_desc,
	(struct usb_descriptor_header *) &gs_header_desc,
	(struct usb_descriptor_header *) &gs_call_mgmt_descriptor,
	(struct usb_descriptor_header *) &gs_acm_descriptor,
	(struct usb_descriptor_header *) &gs_union_desc,
	(struct usb_descriptor_header *) &gs_fullspeed_notify_desc,
	(struct usb_descriptor_header *) &gs_data_interface_desc,
	(struct usb_descriptor_header *) &gs_fullspeed_in_desc,
	(struct usb_descriptor_header *) &gs_fullspeed_out_desc,
	NULL,
};

static struct usb_endpoint_descriptor gs_highspeed_notify_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bEndpointAddress =	USB_DIR_IN,
	.bmAttributes =		USB_ENDPOINT_XFER_INT,
	.wMaxPacketSize =	__constant_cpu_to_le16(GS_NOTIFY_MAXPACKET),
	.bInterval =		GS_LOG2_NOTIFY_INTERVAL+4,
};

static struct usb_endpoint_descriptor gs_highspeed_in_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize =	__constant_cpu_to_le16(512),
};

static struct usb_endpoint_descriptor gs_highspeed_out_desc = {
	.bLength =		USB_DT_ENDPOINT_SIZE,
	.bDescriptorType =	USB_DT_ENDPOINT,
	.bmAttributes =		USB_ENDPOINT_XFER_BULK,
	.wMaxPacketSize =	__constant_cpu_to_le16(512),
};

static struct usb_qualifier_descriptor gs_qualifier_desc = {
	.bLength =		sizeof(struct usb_qualifier_descriptor),
	.bDescriptorType =	USB_DT_DEVICE_QUALIFIER,
	.bcdUSB =		__constant_cpu_to_le16 (0x0200),
	/* assumes ep0 uses the same value for both speeds ... */
	.bNumConfigurations =	GS_NUM_CONFIGS,
};

static const struct usb_descriptor_header *gs_bulk_highspeed_function[] = {
	(struct usb_descriptor_header *) &gs_otg_descriptor,
	(struct usb_descriptor_header *) &gs_bulk_interface_desc,
	(struct usb_descriptor_header *) &gs_highspeed_in_desc,
	(struct usb_descriptor_header *) &gs_highspeed_out_desc,
	NULL,
};

static const struct usb_descriptor_header *gs_acm_highspeed_function[] = {
	(struct usb_descriptor_header *) &gs_otg_descriptor,
	(struct usb_descriptor_header *) &gs_control_interface_desc,
	(struct usb_descriptor_header *) &gs_header_desc,
	(struct usb_descriptor_header *) &gs_call_mgmt_descriptor,
	(struct usb_descriptor_header *) &gs_acm_descriptor,
	(struct usb_descriptor_header *) &gs_union_desc,
	(struct usb_descriptor_header *) &gs_highspeed_notify_desc,
	(struct usb_descriptor_header *) &gs_data_interface_desc,
	(struct usb_descriptor_header *) &gs_highspeed_in_desc,
	(struct usb_descriptor_header *) &gs_highspeed_out_desc,
	NULL,
};


/* Module */
MODULE_DESCRIPTION(GS_LONG_NAME);
MODULE_AUTHOR("Al Borchers");
MODULE_LICENSE("GPL");

#ifdef DEBUG
module_param(debug, int, S_IRUGO|S_IWUSR);
MODULE_PARM_DESC(debug, "Enable debugging, 0=off, 1=on");
#endif

module_param(read_q_size, uint, S_IRUGO);
MODULE_PARM_DESC(read_q_size, "Read request queue size, default=32");

module_param(write_q_size, uint, S_IRUGO);
MODULE_PARM_DESC(write_q_size, "Write request queue size, default=32");

module_param(write_buf_size, uint, S_IRUGO);
MODULE_PARM_DESC(write_buf_size, "Write buffer size, default=8192");

module_param(use_acm, uint, S_IRUGO);
MODULE_PARM_DESC(use_acm, "Use CDC ACM, 0=no, 1=yes, default=no");

module_init(gs_module_init);
module_exit(gs_module_exit);

/*
*  gs_module_init
*
*  Register as a USB gadget driver and a tty driver.
*/
static int __init gs_module_init(void)
{
	int i;
	int retval;

	retval = usb_gadget_register_driver(&gs_gadget_driver);
	if (retval) {
		printk(KERN_ERR "gs_module_init: cannot register gadget driver, ret=%d\n", retval);
		return retval;
	}

	gs_tty_driver = alloc_tty_driver(GS_NUM_PORTS);
	if (!gs_tty_driver)
		return -ENOMEM;
	gs_tty_driver->owner = THIS_MODULE;
	gs_tty_driver->driver_name = GS_SHORT_NAME;
	gs_tty_driver->name = "ttygs";
	gs_tty_driver->major = GS_MAJOR;
	gs_tty_driver->minor_start = GS_MINOR_START;
	gs_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
	gs_tty_driver->subtype = SERIAL_TYPE_NORMAL;
	gs_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
	gs_tty_driver->init_termios = tty_std_termios;
	gs_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
	tty_set_operations(gs_tty_driver, &gs_tty_ops);

	for (i=0; i < GS_NUM_PORTS; i++)
		mutex_init(&gs_open_close_lock[i]);

	retval = tty_register_driver(gs_tty_driver);
	if (retval) {
		usb_gadget_unregister_driver(&gs_gadget_driver);
		put_tty_driver(gs_tty_driver);
		printk(KERN_ERR "gs_module_init: cannot register tty driver, ret=%d\n", retval);
		return retval;
	}