drivers/usb/serial/ch341.c

   1 /*
   2  * Copyright 2007, Frank A Kingswood <frank@kingswood-consulting.co.uk>
   3  * Copyright 2007, Werner Cornelius <werner@cornelius-consult.de>
   4  * Copyright 2009, Boris Hajduk <boris@hajduk.org>
   5  *
   6  * ch341.c implements a serial port driver for the Winchiphead CH341.
   7  *
   8  * The CH341 device can be used to implement an RS232 asynchronous
   9  * serial port, an IEEE-1284 parallel printer port or a memory-like
  10  * interface. In all cases the CH341 supports an I2C interface as well.
  11  * This driver only supports the asynchronous serial interface.
  12  *
  13  * This program is free software; you can redistribute it and/or
  14  * modify it under the terms of the GNU General Public License version
  15  * 2 as published by the Free Software Foundation.
  16  */
  17
  18 #include <linux/kernel.h>
  19 #include <linux/tty.h>
  20 #include <linux/module.h>
  21 #include <linux/slab.h>
  22 #include <linux/usb.h>
  23 #include <linux/usb/serial.h>
  24 #include <linux/serial.h>
  25 #include <asm/unaligned.h>
  26
  27 #define DEFAULT_BAUD_RATE 9600
  28 #define DEFAULT_TIMEOUT   1000
  29
  30 /* flags for IO-Bits */
  31 #define CH341_BIT_RTS (1 << 6)
  32 #define CH341_BIT_DTR (1 << 5)
  33
  34 /******************************/
  35 /* interrupt pipe definitions */
  36 /******************************/
  37 /* always 4 interrupt bytes */
  38 /* first irq byte normally 0x08 */
  39 /* second irq byte base 0x7d + below */
  40 /* third irq byte base 0x94 + below */
  41 /* fourth irq byte normally 0xee */
  42
  43 /* second interrupt byte */
  44 #define CH341_MULT_STAT 0x04 /* multiple status since last interrupt event */
  45
  46 /* status returned in third interrupt answer byte, inverted in data
  47    from irq */
  48 #define CH341_BIT_CTS 0x01
  49 #define CH341_BIT_DSR 0x02
  50 #define CH341_BIT_RI  0x04
  51 #define CH341_BIT_DCD 0x08
  52 #define CH341_BITS_MODEM_STAT 0x0f /* all bits */
  53
  54 /*******************************/
  55 /* baudrate calculation factor */
  56 /*******************************/
  57 #define CH341_BAUDBASE_FACTOR 1532620800
  58 #define CH341_BAUDBASE_DIVMAX 3
  59
  60 /* Break support - the information used to implement this was gleaned from
  61  * the Net/FreeBSD uchcom.c driver by Takanori Watanabe.  Domo arigato.
  62  */
  63
  64 #define CH341_REQ_READ_VERSION 0x5F
  65 #define CH341_REQ_WRITE_REG    0x9A
  66 #define CH341_REQ_READ_REG     0x95
  67 #define CH341_REQ_SERIAL_INIT  0xA1
  68 #define CH341_REQ_MODEM_CTRL   0xA4
  69
  70 #define CH341_REG_BREAK        0x05
  71 #define CH341_REG_LCR          0x18
  72 #define CH341_NBREAK_BITS      0x01
  73
  74 #define CH341_LCR_ENABLE_RX    0x80
  75 #define CH341_LCR_ENABLE_TX    0x40
  76 #define CH341_LCR_MARK_SPACE   0x20
  77 #define CH341_LCR_PAR_EVEN     0x10
  78 #define CH341_LCR_ENABLE_PAR   0x08
  79 #define CH341_LCR_STOP_BITS_2  0x04
  80 #define CH341_LCR_CS8          0x03
  81 #define CH341_LCR_CS7          0x02
  82 #define CH341_LCR_CS6          0x01
  83 #define CH341_LCR_CS5          0x00
  84
  85 static const struct usb_device_id id_table[] = {
  86         { USB_DEVICE(0x4348, 0x5523) },
  87         { USB_DEVICE(0x1a86, 0x7523) },
  88         { USB_DEVICE(0x1a86, 0x5523) },
  89         { },
  90 };
  91 MODULE_DEVICE_TABLE(usb, id_table);
  92
  93 struct ch341_private {
  94         spinlock_t lock; /* access lock */
  95         unsigned baud_rate; /* set baud rate */
  96         u8 mcr;
  97         u8 msr;
  98         u8 lcr;
  99 };
 100
 101 static void ch341_set_termios(struct tty_struct *tty,
 102                               struct usb_serial_port *port,
 103                               struct ktermios *old_termios);
 104
 105 static int ch341_control_out(struct usb_device *dev, u8 request,
 106                              u16 value, u16 index)
 107 {
 108         int r;
 109
 110         dev_dbg(&dev->dev, "%s - (%02x,%04x,%04x)\n", __func__,
 111                 request, value, index);
 112
 113         r = usb_control_msg(dev, usb_sndctrlpipe(dev, 0), request,
 114                             USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
 115                             value, index, NULL, 0, DEFAULT_TIMEOUT);
 116         if (r < 0)
 117                 dev_err(&dev->dev, "failed to send control message: %d\n", r);
 118
 119         return r;
 120 }
 121
 122 static int ch341_control_in(struct usb_device *dev,
 123                             u8 request, u16 value, u16 index,
 124                             char *buf, unsigned bufsize)
 125 {
 126         int r;
 127
 128         dev_dbg(&dev->dev, "%s - (%02x,%04x,%04x,%u)\n", __func__,
 129                 request, value, index, bufsize);
 130
 131         r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), request,
 132                             USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
 133                             value, index, buf, bufsize, DEFAULT_TIMEOUT);
 134         if (r < bufsize) {
 135                 if (r >= 0) {
 136                         dev_err(&dev->dev,
 137                                 "short control message received (%d < %u)\n",
 138                                 r, bufsize);
 139                         r = -EIO;
 140                 }
 141
 142                 dev_err(&dev->dev, "failed to receive control message: %d\n",
 143                         r);
 144                 return r;
 145         }
 146
 147         return 0;
 148 }
 149
 150 static int ch341_set_baudrate_lcr(struct usb_device *dev,
 151                                   struct ch341_private *priv, u8 lcr)
 152 {
 153         short a;
 154         int r;
 155         unsigned long factor;
 156         short divisor;
 157
 158         if (!priv->baud_rate)
 159                 return -EINVAL;
 160         factor = (CH341_BAUDBASE_FACTOR / priv->baud_rate);
 161         divisor = CH341_BAUDBASE_DIVMAX;
 162
 163         while ((factor > 0xfff0) && divisor) {
 164                 factor >>= 3;
 165                 divisor--;
 166         }
 167
 168         if (factor > 0xfff0)
 169                 return -EINVAL;
 170
 171         factor = 0x10000 - factor;
 172         a = (factor & 0xff00) | divisor;
 173
 174         /*
 175          * CH341A buffers data until a full endpoint-size packet (32 bytes)
 176          * has been received unless bit 7 is set.
 177          */
 178         a |= BIT(7);
 179
 180         r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x1312, a);
 181         if (r)
 182                 return r;
 183
 184         r = ch341_control_out(dev, CH341_REQ_WRITE_REG, 0x2518, lcr);
 185         if (r)
 186                 return r;
 187
 188         return r;
 189 }
 190
 191 static int ch341_set_handshake(struct usb_device *dev, u8 control)
 192 {
 193         return ch341_control_out(dev, CH341_REQ_MODEM_CTRL, ~control, 0);
 194 }
 195
 196 static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
 197 {
 198         const unsigned int size = 2;
 199         char *buffer;
 200         int r;
 201         unsigned long flags;
 202
 203         buffer = kmalloc(size, GFP_KERNEL);
 204         if (!buffer)
 205                 return -ENOMEM;
 206
 207         r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, size);
 208         if (r < 0)
 209                 goto out;
 210
 211         spin_lock_irqsave(&priv->lock, flags);
 212         priv->msr = (~(*buffer)) & CH341_BITS_MODEM_STAT;
 213         spin_unlock_irqrestore(&priv->lock, flags);
 214
 215 out:    kfree(buffer);
 216         return r;
 217 }
 218
 219 /* -------------------------------------------------------------------------- */
 220
 221 static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
 222 {
 223         const unsigned int size = 2;
 224         char *buffer;
 225         int r;
 226
 227         buffer = kmalloc(size, GFP_KERNEL);
 228         if (!buffer)
 229                 return -ENOMEM;
 230
 231         /* expect two bytes 0x27 0x00 */
 232         r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
 233         if (r < 0)
 234                 goto out;
 235         dev_dbg(&dev->dev, "Chip version: 0x%02x\n", buffer[0]);
 236
 237         r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
 238         if (r < 0)
 239                 goto out;
 240
 241         r = ch341_set_baudrate_lcr(dev, priv, priv->lcr);
 242         if (r < 0)
 243                 goto out;
 244
 245         r = ch341_set_handshake(dev, priv->mcr);
 246
 247 out:    kfree(buffer);
 248         return r;
 249 }
 250
 251 static int ch341_port_probe(struct usb_serial_port *port)
 252 {
 253         struct ch341_private *priv;
 254         int r;
 255
 256         priv = kzalloc(sizeof(struct ch341_private), GFP_KERNEL);
 257         if (!priv)
 258                 return -ENOMEM;
 259
 260         spin_lock_init(&priv->lock);
 261         priv->baud_rate = DEFAULT_BAUD_RATE;
 262         /*
 263          * Some CH340 devices appear unable to change the initial LCR
 264          * settings, so set a sane 8N1 default.
 265          */
 266         priv->lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8;
 267
 268         r = ch341_configure(port->serial->dev, priv);
 269         if (r < 0)
 270                 goto error;
 271
 272         usb_set_serial_port_data(port, priv);
 273         return 0;
 274
 275 error:  kfree(priv);
 276         return r;
 277 }
 278
 279 static int ch341_port_remove(struct usb_serial_port *port)
 280 {
 281         struct ch341_private *priv;
 282
 283         priv = usb_get_serial_port_data(port);
 284         kfree(priv);
 285
 286         return 0;
 287 }
 288
 289 static int ch341_carrier_raised(struct usb_serial_port *port)
 290 {
 291         struct ch341_private *priv = usb_get_serial_port_data(port);
 292         if (priv->msr & CH341_BIT_DCD)
 293                 return 1;
 294         return 0;
 295 }
 296
 297 static void ch341_dtr_rts(struct usb_serial_port *port, int on)
 298 {
 299         struct ch341_private *priv = usb_get_serial_port_data(port);
 300         unsigned long flags;
 301
 302         /* drop DTR and RTS */
 303         spin_lock_irqsave(&priv->lock, flags);
 304         if (on)
 305                 priv->mcr |= CH341_BIT_RTS | CH341_BIT_DTR;
 306         else
 307                 priv->mcr &= ~(CH341_BIT_RTS | CH341_BIT_DTR);
 308         spin_unlock_irqrestore(&priv->lock, flags);
 309         ch341_set_handshake(port->serial->dev, priv->mcr);
 310 }
 311
 312 static void ch341_close(struct usb_serial_port *port)
 313 {
 314         usb_serial_generic_close(port);
 315         usb_kill_urb(port->interrupt_in_urb);
 316 }
 317
 318
 319 /* open this device, set default parameters */
 320 static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port)
 321 {
 322         struct ch341_private *priv = usb_get_serial_port_data(port);
 323         int r;
 324
 325         if (tty)
 326                 ch341_set_termios(tty, port, NULL);
 327
 328         dev_dbg(&port->dev, "%s - submitting interrupt urb\n", __func__);
 329         r = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
 330         if (r) {
 331                 dev_err(&port->dev, "%s - failed to submit interrupt urb: %d\n",
 332                         __func__, r);
 333                 return r;
 334         }
 335
 336         r = ch341_get_status(port->serial->dev, priv);
 337         if (r < 0) {
 338                 dev_err(&port->dev, "failed to read modem status: %d\n", r);
 339                 goto err_kill_interrupt_urb;
 340         }
 341
 342         r = usb_serial_generic_open(tty, port);
 343         if (r)
 344                 goto err_kill_interrupt_urb;
 345
 346         return 0;
 347
 348 err_kill_interrupt_urb:
 349         usb_kill_urb(port->interrupt_in_urb);
 350
 351         return r;
 352 }
 353
 354 /* Old_termios contains the original termios settings and
 355  * tty->termios contains the new setting to be used.
 356  */
 357 static void ch341_set_termios(struct tty_struct *tty,
 358                 struct usb_serial_port *port, struct ktermios *old_termios)
 359 {
 360         struct ch341_private *priv = usb_get_serial_port_data(port);
 361         unsigned baud_rate;
 362         unsigned long flags;
 363         u8 lcr;
 364         int r;
 365
 366         /* redundant changes may cause the chip to lose bytes */
 367         if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
 368                 return;
 369
 370         baud_rate = tty_get_baud_rate(tty);
 371
 372         lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX;
 373
 374         switch (C_CSIZE(tty)) {
 375         case CS5:
 376                 lcr |= CH341_LCR_CS5;
 377                 break;
 378         case CS6:
 379                 lcr |= CH341_LCR_CS6;
 380                 break;
 381         case CS7:
 382                 lcr |= CH341_LCR_CS7;
 383                 break;
 384         case CS8:
 385                 lcr |= CH341_LCR_CS8;
 386                 break;
 387         }
 388
 389         if (C_PARENB(tty)) {
 390                 lcr |= CH341_LCR_ENABLE_PAR;
 391                 if (C_PARODD(tty) == 0)
 392                         lcr |= CH341_LCR_PAR_EVEN;
 393                 if (C_CMSPAR(tty))
 394                         lcr |= CH341_LCR_MARK_SPACE;
 395         }
 396
 397         if (C_CSTOPB(tty))
 398                 lcr |= CH341_LCR_STOP_BITS_2;
 399
 400         if (baud_rate) {
 401                 priv->baud_rate = baud_rate;
 402
 403                 r = ch341_set_baudrate_lcr(port->serial->dev, priv, lcr);
 404                 if (r < 0 && old_termios) {
 405                         priv->baud_rate = tty_termios_baud_rate(old_termios);
 406                         tty_termios_copy_hw(&tty->termios, old_termios);
 407                 } else if (r == 0) {
 408                         priv->lcr = lcr;
 409                 }
 410         }
 411
 412         spin_lock_irqsave(&priv->lock, flags);
 413         if (C_BAUD(tty) == B0)
 414                 priv->mcr &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
 415         else if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
 416                 priv->mcr |= (CH341_BIT_DTR | CH341_BIT_RTS);
 417         spin_unlock_irqrestore(&priv->lock, flags);
 418
 419         ch341_set_handshake(port->serial->dev, priv->mcr);
 420 }
 421
 422 static void ch341_break_ctl(struct tty_struct *tty, int break_state)
 423 {
 424         const uint16_t ch341_break_reg =
 425                         ((uint16_t) CH341_REG_LCR << 8) | CH341_REG_BREAK;
 426         struct usb_serial_port *port = tty->driver_data;
 427         int r;
 428         uint16_t reg_contents;
 429         uint8_t *break_reg;
 430
 431         break_reg = kmalloc(2, GFP_KERNEL);
 432         if (!break_reg)
 433                 return;
 434
 435         r = ch341_control_in(port->serial->dev, CH341_REQ_READ_REG,
 436                         ch341_break_reg, 0, break_reg, 2);
 437         if (r < 0) {
 438                 dev_err(&port->dev, "%s - USB control read error (%d)\n",
 439                                 __func__, r);
 440                 goto out;
 441         }
 442         dev_dbg(&port->dev, "%s - initial ch341 break register contents - reg1: %x, reg2: %x\n",
 443                 __func__, break_reg[0], break_reg[1]);
 444         if (break_state != 0) {
 445                 dev_dbg(&port->dev, "%s - Enter break state requested\n", __func__);
 446                 break_reg[0] &= ~CH341_NBREAK_BITS;
 447                 break_reg[1] &= ~CH341_LCR_ENABLE_TX;
 448         } else {
 449                 dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
 450                 break_reg[0] |= CH341_NBREAK_BITS;
 451                 break_reg[1] |= CH341_LCR_ENABLE_TX;
 452         }
 453         dev_dbg(&port->dev, "%s - New ch341 break register contents - reg1: %x, reg2: %x\n",
 454                 __func__, break_reg[0], break_reg[1]);
 455         reg_contents = get_unaligned_le16(break_reg);
 456         r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG,
 457                         ch341_break_reg, reg_contents);
 458         if (r < 0)
 459                 dev_err(&port->dev, "%s - USB control write error (%d)\n",
 460                                 __func__, r);
 461 out:
 462         kfree(break_reg);
 463 }
 464
 465 static int ch341_tiocmset(struct tty_struct *tty,
 466                           unsigned int set, unsigned int clear)
 467 {
 468         struct usb_serial_port *port = tty->driver_data;
 469         struct ch341_private *priv = usb_get_serial_port_data(port);
 470         unsigned long flags;
 471         u8 control;
 472
 473         spin_lock_irqsave(&priv->lock, flags);
 474         if (set & TIOCM_RTS)
 475                 priv->mcr |= CH341_BIT_RTS;
 476         if (set & TIOCM_DTR)
 477                 priv->mcr |= CH341_BIT_DTR;
 478         if (clear & TIOCM_RTS)
 479                 priv->mcr &= ~CH341_BIT_RTS;
 480         if (clear & TIOCM_DTR)
 481                 priv->mcr &= ~CH341_BIT_DTR;
 482         control = priv->mcr;
 483         spin_unlock_irqrestore(&priv->lock, flags);
 484
 485         return ch341_set_handshake(port->serial->dev, control);
 486 }
 487
 488 static void ch341_update_status(struct usb_serial_port *port,
 489                                         unsigned char *data, size_t len)
 490 {
 491         struct ch341_private *priv = usb_get_serial_port_data(port);
 492         struct tty_struct *tty;
 493         unsigned long flags;
 494         u8 status;
 495         u8 delta;
 496
 497         if (len < 4)
 498                 return;
 499
 500         status = ~data[2] & CH341_BITS_MODEM_STAT;
 501
 502         spin_lock_irqsave(&priv->lock, flags);
 503         delta = status ^ priv->msr;
 504         priv->msr = status;
 505         spin_unlock_irqrestore(&priv->lock, flags);
 506
 507         if (data[1] & CH341_MULT_STAT)
 508                 dev_dbg(&port->dev, "%s - multiple status change\n", __func__);
 509
 510         if (!delta)
 511                 return;
 512
 513         if (delta & CH341_BIT_CTS)
 514                 port->icount.cts++;
 515         if (delta & CH341_BIT_DSR)
 516                 port->icount.dsr++;
 517         if (delta & CH341_BIT_RI)
 518                 port->icount.rng++;
 519         if (delta & CH341_BIT_DCD) {
 520                 port->icount.dcd++;
 521                 tty = tty_port_tty_get(&port->port);
 522                 if (tty) {
 523                         usb_serial_handle_dcd_change(port, tty,
 524                                                 status & CH341_BIT_DCD);
 525                         tty_kref_put(tty);
 526                 }
 527         }
 528
 529         wake_up_interruptible(&port->port.delta_msr_wait);
 530 }
 531
 532 static void ch341_read_int_callback(struct urb *urb)
 533 {
 534         struct usb_serial_port *port = urb->context;
 535         unsigned char *data = urb->transfer_buffer;
 536         unsigned int len = urb->actual_length;
 537         int status;
 538
 539         switch (urb->status) {
 540         case 0:
 541                 /* success */
 542                 break;
 543         case -ECONNRESET:
 544         case -ENOENT:
 545         case -ESHUTDOWN:
 546                 /* this urb is terminated, clean up */
 547                 dev_dbg(&urb->dev->dev, "%s - urb shutting down: %d\n",
 548                         __func__, urb->status);
 549                 return;
 550         default:
 551                 dev_dbg(&urb->dev->dev, "%s - nonzero urb status: %d\n",
 552                         __func__, urb->status);
 553                 goto exit;
 554         }
 555
 556         usb_serial_debug_data(&port->dev, __func__, len, data);
 557         ch341_update_status(port, data, len);
 558 exit:
 559         status = usb_submit_urb(urb, GFP_ATOMIC);
 560         if (status) {
 561                 dev_err(&urb->dev->dev, "%s - usb_submit_urb failed: %d\n",
 562                         __func__, status);
 563         }
 564 }
 565
 566 static int ch341_tiocmget(struct tty_struct *tty)
 567 {
 568         struct usb_serial_port *port = tty->driver_data;
 569         struct ch341_private *priv = usb_get_serial_port_data(port);
 570         unsigned long flags;
 571         u8 mcr;
 572         u8 status;
 573         unsigned int result;
 574
 575         spin_lock_irqsave(&priv->lock, flags);
 576         mcr = priv->mcr;
 577         status = priv->msr;
 578         spin_unlock_irqrestore(&priv->lock, flags);
 579
 580         result = ((mcr & CH341_BIT_DTR)         ? TIOCM_DTR : 0)
 581                   | ((mcr & CH341_BIT_RTS)      ? TIOCM_RTS : 0)
 582                   | ((status & CH341_BIT_CTS)   ? TIOCM_CTS : 0)
 583                   | ((status & CH341_BIT_DSR)   ? TIOCM_DSR : 0)
 584                   | ((status & CH341_BIT_RI)    ? TIOCM_RI  : 0)
 585                   | ((status & CH341_BIT_DCD)   ? TIOCM_CD  : 0);
 586
 587         dev_dbg(&port->dev, "%s - result = %x\n", __func__, result);
 588
 589         return result;
 590 }
 591
 592 static int ch341_reset_resume(struct usb_serial *serial)
 593 {
 594         struct usb_serial_port *port = serial->port[0];
 595         struct ch341_private *priv = usb_get_serial_port_data(port);
 596         int ret;
 597
 598         /* reconfigure ch341 serial port after bus-reset */
 599         ch341_configure(serial->dev, priv);
 600
 601         if (tty_port_initialized(&port->port)) {
 602                 ret = usb_submit_urb(port->interrupt_in_urb, GFP_NOIO);
 603                 if (ret) {
 604                         dev_err(&port->dev, "failed to submit interrupt urb: %d\n",
 605                                 ret);
 606                         return ret;
 607                 }
 608
 609                 ret = ch341_get_status(port->serial->dev, priv);
 610                 if (ret < 0) {
 611                         dev_err(&port->dev, "failed to read modem status: %d\n",
 612                                 ret);
 613                 }
 614         }
 615
 616         return usb_serial_generic_resume(serial);
 617 }
 618
 619 static struct usb_serial_driver ch341_device = {
 620         .driver = {
 621                 .owner  = THIS_MODULE,
 622                 .name   = "ch341-uart",
 623         },
 624         .id_table          = id_table,
 625         .num_ports         = 1,
 626         .open              = ch341_open,
 627         .dtr_rts           = ch341_dtr_rts,
 628         .carrier_raised    = ch341_carrier_raised,
 629         .close             = ch341_close,
 630         .set_termios       = ch341_set_termios,
 631         .break_ctl         = ch341_break_ctl,
 632         .tiocmget          = ch341_tiocmget,
 633         .tiocmset          = ch341_tiocmset,
 634         .tiocmiwait        = usb_serial_generic_tiocmiwait,
 635         .read_int_callback = ch341_read_int_callback,
 636         .port_probe        = ch341_port_probe,
 637         .port_remove       = ch341_port_remove,
 638         .reset_resume      = ch341_reset_resume,
 639 };
 640
 641 static struct usb_serial_driver * const serial_drivers[] = {
 642         &ch341_device, NULL
 643 };
 644
 645 module_usb_serial_driver(serial_drivers, id_table);
 646
 647 MODULE_LICENSE("GPL");