1 // SPDX-License-Identifier: GPL-2.0+ 2 /* 3 * Copyright (C) 2009 by Bart Hartgers (bart.hartgers+ark3116@gmail.com) 4 * Original version: 5 * Copyright (C) 2006 6 * Simon Schulz (ark3116_driver <at> auctionant.de) 7 * 8 * ark3116 9 * - implements a driver for the arkmicro ark3116 chipset (vendor=0x6547, 10 * productid=0x0232) (used in a datacable called KQ-U8A) 11 * 12 * Supports full modem status lines, break, hardware flow control. Does not 13 * support software flow control, since I do not know how to enable it in hw. 14 * 15 * This driver is a essentially new implementation. I initially dug 16 * into the old ark3116.c driver and suddenly realized the ark3116 is 17 * a 16450 with a USB interface glued to it. See comments at the 18 * bottom of this file. 19 */ 20 21 #include <linux/kernel.h> 22 #include <linux/ioctl.h> 23 #include <linux/tty.h> 24 #include <linux/slab.h> 25 #include <linux/tty_flip.h> 26 #include <linux/module.h> 27 #include <linux/usb.h> 28 #include <linux/usb/serial.h> 29 #include <linux/serial.h> 30 #include <linux/serial_reg.h> 31 #include <linux/uaccess.h> 32 #include <linux/mutex.h> 33 #include <linux/spinlock.h> 34 35 #define DRIVER_AUTHOR "Bart Hartgers <bart.hartgers+ark3116@gmail.com>" 36 #define DRIVER_DESC "USB ARK3116 serial/IrDA driver" 37 #define DRIVER_DEV_DESC "ARK3116 RS232/IrDA" 38 #define DRIVER_NAME "ark3116" 39 40 /* usb timeout of 1 second */ 41 #define ARK_TIMEOUT 1000 42 43 static const struct usb_device_id id_table[] = { 44 { USB_DEVICE(0x6547, 0x0232) }, 45 { USB_DEVICE(0x18ec, 0x3118) }, /* USB to IrDA adapter */ 46 { }, 47 }; 48 MODULE_DEVICE_TABLE(usb, id_table); 49 50 static int is_irda(struct usb_serial *serial) 51 { 52 struct usb_device *dev = serial->dev; 53 if (le16_to_cpu(dev->descriptor.idVendor) == 0x18ec && 54 le16_to_cpu(dev->descriptor.idProduct) == 0x3118) 55 return 1; 56 return 0; 57 } 58 59 struct ark3116_private { 60 int irda; /* 1 for irda device */ 61 62 /* protects hw register updates */ 63 struct mutex hw_lock; 64 65 int quot; /* baudrate divisor */ 66 __u32 lcr; /* line control register value */ 67 __u32 hcr; /* handshake control register (0x8) 68 * value */ 69 __u32 mcr; /* modem control register value */ 70 71 /* protects the status values below */ 72 spinlock_t status_lock; 73 __u32 msr; /* modem status register value */ 74 __u32 lsr; /* line status register value */ 75 }; 76 77 static int ark3116_write_reg(struct usb_serial *serial, 78 unsigned reg, __u8 val) 79 { 80 int result; 81 /* 0xfe 0x40 are magic values taken from original driver */ 82 result = usb_control_msg(serial->dev, 83 usb_sndctrlpipe(serial->dev, 0), 84 0xfe, 0x40, val, reg, 85 NULL, 0, ARK_TIMEOUT); 86 if (result) 87 return result; 88 89 return 0; 90 } 91 92 static int ark3116_read_reg(struct usb_serial *serial, 93 unsigned reg, unsigned char *buf) 94 { 95 int result; 96 /* 0xfe 0xc0 are magic values taken from original driver */ 97 result = usb_control_msg(serial->dev, 98 usb_rcvctrlpipe(serial->dev, 0), 99 0xfe, 0xc0, 0, reg, 100 buf, 1, ARK_TIMEOUT); 101 if (result < 1) { 102 dev_err(&serial->interface->dev, 103 "failed to read register %u: %d\n", 104 reg, result); 105 if (result >= 0) 106 result = -EIO; 107 108 return result; 109 } 110 111 return 0; 112 } 113 114 static inline int calc_divisor(int bps) 115 { 116 /* Original ark3116 made some exceptions in rounding here 117 * because windows did the same. Assume that is not really 118 * necessary. 119 * Crystal is 12MHz, probably because of USB, but we divide by 4? 120 */ 121 return (12000000 + 2*bps) / (4*bps); 122 } 123 124 static int ark3116_port_probe(struct usb_serial_port *port) 125 { 126 struct usb_serial *serial = port->serial; 127 struct ark3116_private *priv; 128 129 priv = kzalloc(sizeof(*priv), GFP_KERNEL); 130 if (!priv) 131 return -ENOMEM; 132 133 mutex_init(&priv->hw_lock); 134 spin_lock_init(&priv->status_lock); 135 136 priv->irda = is_irda(serial); 137 138 usb_set_serial_port_data(port, priv); 139 140 /* setup the hardware */ 141 ark3116_write_reg(serial, UART_IER, 0); 142 /* disable DMA */ 143 ark3116_write_reg(serial, UART_FCR, 0); 144 /* handshake control */ 145 priv->hcr = 0; 146 ark3116_write_reg(serial, 0x8 , 0); 147 /* modem control */ 148 priv->mcr = 0; 149 ark3116_write_reg(serial, UART_MCR, 0); 150 151 if (!(priv->irda)) { 152 ark3116_write_reg(serial, 0xb , 0); 153 } else { 154 ark3116_write_reg(serial, 0xb , 1); 155 ark3116_write_reg(serial, 0xc , 0); 156 ark3116_write_reg(serial, 0xd , 0x41); 157 ark3116_write_reg(serial, 0xa , 1); 158 } 159 160 /* setup baudrate */ 161 ark3116_write_reg(serial, UART_LCR, UART_LCR_DLAB); 162 163 /* setup for 9600 8N1 */ 164 priv->quot = calc_divisor(9600); 165 ark3116_write_reg(serial, UART_DLL, priv->quot & 0xff); 166 ark3116_write_reg(serial, UART_DLM, (priv->quot>>8) & 0xff); 167 168 priv->lcr = UART_LCR_WLEN8; 169 ark3116_write_reg(serial, UART_LCR, UART_LCR_WLEN8); 170 171 ark3116_write_reg(serial, 0xe, 0); 172 173 if (priv->irda) 174 ark3116_write_reg(serial, 0x9, 0); 175 176 dev_info(&port->dev, "using %s mode\n", priv->irda ? "IrDA" : "RS232"); 177 178 return 0; 179 } 180 181 static void ark3116_port_remove(struct usb_serial_port *port) 182 { 183 struct ark3116_private *priv = usb_get_serial_port_data(port); 184 185 /* device is closed, so URBs and DMA should be down */ 186 mutex_destroy(&priv->hw_lock); 187 kfree(priv); 188 } 189 190 static void ark3116_set_termios(struct tty_struct *tty, 191 struct usb_serial_port *port, 192 const struct ktermios *old_termios) 193 { 194 struct usb_serial *serial = port->serial; 195 struct ark3116_private *priv = usb_get_serial_port_data(port); 196 struct ktermios *termios = &tty->termios; 197 unsigned int cflag = termios->c_cflag; 198 int bps = tty_get_baud_rate(tty); 199 int quot; 200 __u8 lcr, hcr, eval; 201 202 /* set data bit count */ 203 lcr = UART_LCR_WLEN(tty_get_char_size(cflag)); 204 205 if (cflag & CSTOPB) 206 lcr |= UART_LCR_STOP; 207 if (cflag & PARENB) 208 lcr |= UART_LCR_PARITY; 209 if (!(cflag & PARODD)) 210 lcr |= UART_LCR_EPAR; 211 if (cflag & CMSPAR) 212 lcr |= UART_LCR_SPAR; 213 214 /* handshake control */ 215 hcr = (cflag & CRTSCTS) ? 0x03 : 0x00; 216 217 /* calc baudrate */ 218 dev_dbg(&port->dev, "%s - setting bps to %d\n", __func__, bps); 219 eval = 0; 220 switch (bps) { 221 case 0: 222 quot = calc_divisor(9600); 223 break; 224 default: 225 if ((bps < 75) || (bps > 3000000)) 226 bps = 9600; 227 quot = calc_divisor(bps); 228 break; 229 case 460800: 230 eval = 1; 231 quot = calc_divisor(bps); 232 break; 233 case 921600: 234 eval = 2; 235 quot = calc_divisor(bps); 236 break; 237 } 238 239 /* Update state: synchronize */ 240 mutex_lock(&priv->hw_lock); 241 242 /* keep old LCR_SBC bit */ 243 lcr |= (priv->lcr & UART_LCR_SBC); 244 245 dev_dbg(&port->dev, "%s - setting hcr:0x%02x,lcr:0x%02x,quot:%d\n", 246 __func__, hcr, lcr, quot); 247 248 /* handshake control */ 249 if (priv->hcr != hcr) { 250 priv->hcr = hcr; 251 ark3116_write_reg(serial, 0x8, hcr); 252 } 253 254 /* baudrate */ 255 if (priv->quot != quot) { 256 priv->quot = quot; 257 priv->lcr = lcr; /* need to write lcr anyway */ 258 259 /* disable DMA since transmit/receive is 260 * shadowed by UART_DLL 261 */ 262 ark3116_write_reg(serial, UART_FCR, 0); 263 264 ark3116_write_reg(serial, UART_LCR, 265 lcr|UART_LCR_DLAB); 266 ark3116_write_reg(serial, UART_DLL, quot & 0xff); 267 ark3116_write_reg(serial, UART_DLM, (quot>>8) & 0xff); 268 269 /* restore lcr */ 270 ark3116_write_reg(serial, UART_LCR, lcr); 271 /* magic baudrate thingy: not sure what it does, 272 * but windows does this as well. 273 */ 274 ark3116_write_reg(serial, 0xe, eval); 275 276 /* enable DMA */ 277 ark3116_write_reg(serial, UART_FCR, UART_FCR_DMA_SELECT); 278 } else if (priv->lcr != lcr) { 279 priv->lcr = lcr; 280 ark3116_write_reg(serial, UART_LCR, lcr); 281 } 282 283 mutex_unlock(&priv->hw_lock); 284 285 /* check for software flow control */ 286 if (I_IXOFF(tty) || I_IXON(tty)) { 287 dev_warn(&port->dev, 288 "software flow control not implemented\n"); 289 } 290 291 /* Don't rewrite B0 */ 292 if (tty_termios_baud_rate(termios)) 293 tty_termios_encode_baud_rate(termios, bps, bps); 294 } 295 296 static void ark3116_close(struct usb_serial_port *port) 297 { 298 struct usb_serial *serial = port->serial; 299 300 /* disable DMA */ 301 ark3116_write_reg(serial, UART_FCR, 0); 302 303 /* deactivate interrupts */ 304 ark3116_write_reg(serial, UART_IER, 0); 305 306 usb_serial_generic_close(port); 307 308 usb_kill_urb(port->interrupt_in_urb); 309 } 310 311 static int ark3116_open(struct tty_struct *tty, struct usb_serial_port *port) 312 { 313 struct ark3116_private *priv = usb_get_serial_port_data(port); 314 struct usb_serial *serial = port->serial; 315 unsigned char *buf; 316 int result; 317 318 buf = kmalloc(1, GFP_KERNEL); 319 if (buf == NULL) 320 return -ENOMEM; 321 322 result = usb_serial_generic_open(tty, port); 323 if (result) { 324 dev_dbg(&port->dev, 325 "%s - usb_serial_generic_open failed: %d\n", 326 __func__, result); 327 goto err_free; 328 } 329 330 /* remove any data still left: also clears error state */ 331 ark3116_read_reg(serial, UART_RX, buf); 332 333 /* read modem status */ 334 result = ark3116_read_reg(serial, UART_MSR, buf); 335 if (result) 336 goto err_close; 337 priv->msr = *buf; 338 339 /* read line status */ 340 result = ark3116_read_reg(serial, UART_LSR, buf); 341 if (result) 342 goto err_close; 343 priv->lsr = *buf; 344 345 result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL); 346 if (result) { 347 dev_err(&port->dev, "submit irq_in urb failed %d\n", 348 result); 349 goto err_close; 350 } 351 352 /* activate interrupts */ 353 ark3116_write_reg(port->serial, UART_IER, UART_IER_MSI|UART_IER_RLSI); 354 355 /* enable DMA */ 356 ark3116_write_reg(port->serial, UART_FCR, UART_FCR_DMA_SELECT); 357 358 /* setup termios */ 359 if (tty) 360 ark3116_set_termios(tty, port, NULL); 361 362 kfree(buf); 363 364 return 0; 365 366 err_close: 367 usb_serial_generic_close(port); 368 err_free: 369 kfree(buf); 370 371 return result; 372 } 373 374 static int ark3116_tiocmget(struct tty_struct *tty) 375 { 376 struct usb_serial_port *port = tty->driver_data; 377 struct ark3116_private *priv = usb_get_serial_port_data(port); 378 __u32 status; 379 __u32 ctrl; 380 unsigned long flags; 381 382 mutex_lock(&priv->hw_lock); 383 ctrl = priv->mcr; 384 mutex_unlock(&priv->hw_lock); 385 386 spin_lock_irqsave(&priv->status_lock, flags); 387 status = priv->msr; 388 spin_unlock_irqrestore(&priv->status_lock, flags); 389 390 return (status & UART_MSR_DSR ? TIOCM_DSR : 0) | 391 (status & UART_MSR_CTS ? TIOCM_CTS : 0) | 392 (status & UART_MSR_RI ? TIOCM_RI : 0) | 393 (status & UART_MSR_DCD ? TIOCM_CD : 0) | 394 (ctrl & UART_MCR_DTR ? TIOCM_DTR : 0) | 395 (ctrl & UART_MCR_RTS ? TIOCM_RTS : 0) | 396 (ctrl & UART_MCR_OUT1 ? TIOCM_OUT1 : 0) | 397 (ctrl & UART_MCR_OUT2 ? TIOCM_OUT2 : 0); 398 } 399 400 static int ark3116_tiocmset(struct tty_struct *tty, 401 unsigned set, unsigned clr) 402 { 403 struct usb_serial_port *port = tty->driver_data; 404 struct ark3116_private *priv = usb_get_serial_port_data(port); 405 406 /* we need to take the mutex here, to make sure that the value 407 * in priv->mcr is actually the one that is in the hardware 408 */ 409 410 mutex_lock(&priv->hw_lock); 411 412 if (set & TIOCM_RTS) 413 priv->mcr |= UART_MCR_RTS; 414 if (set & TIOCM_DTR) 415 priv->mcr |= UART_MCR_DTR; 416 if (set & TIOCM_OUT1) 417 priv->mcr |= UART_MCR_OUT1; 418 if (set & TIOCM_OUT2) 419 priv->mcr |= UART_MCR_OUT2; 420 if (clr & TIOCM_RTS) 421 priv->mcr &= ~UART_MCR_RTS; 422 if (clr & TIOCM_DTR) 423 priv->mcr &= ~UART_MCR_DTR; 424 if (clr & TIOCM_OUT1) 425 priv->mcr &= ~UART_MCR_OUT1; 426 if (clr & TIOCM_OUT2) 427 priv->mcr &= ~UART_MCR_OUT2; 428 429 ark3116_write_reg(port->serial, UART_MCR, priv->mcr); 430 431 mutex_unlock(&priv->hw_lock); 432 433 return 0; 434 } 435 436 static void ark3116_break_ctl(struct tty_struct *tty, int break_state) 437 { 438 struct usb_serial_port *port = tty->driver_data; 439 struct ark3116_private *priv = usb_get_serial_port_data(port); 440 441 /* LCR is also used for other things: protect access */ 442 mutex_lock(&priv->hw_lock); 443 444 if (break_state) 445 priv->lcr |= UART_LCR_SBC; 446 else 447 priv->lcr &= ~UART_LCR_SBC; 448 449 ark3116_write_reg(port->serial, UART_LCR, priv->lcr); 450 451 mutex_unlock(&priv->hw_lock); 452 } 453 454 static void ark3116_update_msr(struct usb_serial_port *port, __u8 msr) 455 { 456 struct ark3116_private *priv = usb_get_serial_port_data(port); 457 unsigned long flags; 458 459 spin_lock_irqsave(&priv->status_lock, flags); 460 priv->msr = msr; 461 spin_unlock_irqrestore(&priv->status_lock, flags); 462 463 if (msr & UART_MSR_ANY_DELTA) { 464 /* update input line counters */ 465 if (msr & UART_MSR_DCTS) 466 port->icount.cts++; 467 if (msr & UART_MSR_DDSR) 468 port->icount.dsr++; 469 if (msr & UART_MSR_DDCD) 470 port->icount.dcd++; 471 if (msr & UART_MSR_TERI) 472 port->icount.rng++; 473 wake_up_interruptible(&port->port.delta_msr_wait); 474 } 475 } 476 477 static void ark3116_update_lsr(struct usb_serial_port *port, __u8 lsr) 478 { 479 struct ark3116_private *priv = usb_get_serial_port_data(port); 480 unsigned long flags; 481 482 spin_lock_irqsave(&priv->status_lock, flags); 483 /* combine bits */ 484 priv->lsr |= lsr; 485 spin_unlock_irqrestore(&priv->status_lock, flags); 486 487 if (lsr&UART_LSR_BRK_ERROR_BITS) { 488 if (lsr & UART_LSR_BI) 489 port->icount.brk++; 490 if (lsr & UART_LSR_FE) 491 port->icount.frame++; 492 if (lsr & UART_LSR_PE) 493 port->icount.parity++; 494 if (lsr & UART_LSR_OE) 495 port->icount.overrun++; 496 } 497 } 498 499 static void ark3116_read_int_callback(struct urb *urb) 500 { 501 struct usb_serial_port *port = urb->context; 502 int status = urb->status; 503 const __u8 *data = urb->transfer_buffer; 504 int result; 505 506 switch (status) { 507 case -ECONNRESET: 508 case -ENOENT: 509 case -ESHUTDOWN: 510 /* this urb is terminated, clean up */ 511 dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n", 512 __func__, status); 513 return; 514 default: 515 dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n", 516 __func__, status); 517 break; 518 case 0: /* success */ 519 /* discovered this by trail and error... */ 520 if ((urb->actual_length == 4) && (data[0] == 0xe8)) { 521 const __u8 id = data[1]&UART_IIR_ID; 522 dev_dbg(&port->dev, "%s: iir=%02x\n", __func__, data[1]); 523 if (id == UART_IIR_MSI) { 524 dev_dbg(&port->dev, "%s: msr=%02x\n", 525 __func__, data[3]); 526 ark3116_update_msr(port, data[3]); 527 break; 528 } else if (id == UART_IIR_RLSI) { 529 dev_dbg(&port->dev, "%s: lsr=%02x\n", 530 __func__, data[2]); 531 ark3116_update_lsr(port, data[2]); 532 break; 533 } 534 } 535 /* 536 * Not sure what this data meant... 537 */ 538 usb_serial_debug_data(&port->dev, __func__, 539 urb->actual_length, 540 urb->transfer_buffer); 541 break; 542 } 543 544 result = usb_submit_urb(urb, GFP_ATOMIC); 545 if (result) 546 dev_err(&port->dev, "failed to resubmit interrupt urb: %d\n", 547 result); 548 } 549 550 551 /* Data comes in via the bulk (data) URB, errors/interrupts via the int URB. 552 * This means that we cannot be sure which data byte has an associated error 553 * condition, so we report an error for all data in the next bulk read. 554 * 555 * Actually, there might even be a window between the bulk data leaving the 556 * ark and reading/resetting the lsr in the read_bulk_callback where an 557 * interrupt for the next data block could come in. 558 * Without somekind of ordering on the ark, we would have to report the 559 * error for the next block of data as well... 560 * For now, let's pretend this can't happen. 561 */ 562 static void ark3116_process_read_urb(struct urb *urb) 563 { 564 struct usb_serial_port *port = urb->context; 565 struct ark3116_private *priv = usb_get_serial_port_data(port); 566 unsigned char *data = urb->transfer_buffer; 567 char tty_flag = TTY_NORMAL; 568 unsigned long flags; 569 __u32 lsr; 570 571 /* update line status */ 572 spin_lock_irqsave(&priv->status_lock, flags); 573 lsr = priv->lsr; 574 priv->lsr &= ~UART_LSR_BRK_ERROR_BITS; 575 spin_unlock_irqrestore(&priv->status_lock, flags); 576 577 if (!urb->actual_length) 578 return; 579 580 if (lsr & UART_LSR_BRK_ERROR_BITS) { 581 if (lsr & UART_LSR_BI) 582 tty_flag = TTY_BREAK; 583 else if (lsr & UART_LSR_PE) 584 tty_flag = TTY_PARITY; 585 else if (lsr & UART_LSR_FE) 586 tty_flag = TTY_FRAME; 587 588 /* overrun is special, not associated with a char */ 589 if (lsr & UART_LSR_OE) 590 tty_insert_flip_char(&port->port, 0, TTY_OVERRUN); 591 } 592 tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag, 593 urb->actual_length); 594 tty_flip_buffer_push(&port->port); 595 } 596 597 static struct usb_serial_driver ark3116_device = { 598 .driver = { 599 .owner = THIS_MODULE, 600 .name = "ark3116", 601 }, 602 .id_table = id_table, 603 .num_ports = 1, 604 .num_bulk_in = 1, 605 .num_bulk_out = 1, 606 .num_interrupt_in = 1, 607 .port_probe = ark3116_port_probe, 608 .port_remove = ark3116_port_remove, 609 .set_termios = ark3116_set_termios, 610 .tiocmget = ark3116_tiocmget, 611 .tiocmset = ark3116_tiocmset, 612 .tiocmiwait = usb_serial_generic_tiocmiwait, 613 .get_icount = usb_serial_generic_get_icount, 614 .open = ark3116_open, 615 .close = ark3116_close, 616 .break_ctl = ark3116_break_ctl, 617 .read_int_callback = ark3116_read_int_callback, 618 .process_read_urb = ark3116_process_read_urb, 619 }; 620 621 static struct usb_serial_driver * const serial_drivers[] = { 622 &ark3116_device, NULL 623 }; 624 625 module_usb_serial_driver(serial_drivers, id_table); 626 627 MODULE_LICENSE("GPL"); 628 629 MODULE_AUTHOR(DRIVER_AUTHOR); 630 MODULE_DESCRIPTION(DRIVER_DESC); 631 632 /* 633 * The following describes what I learned from studying the old 634 * ark3116.c driver, disassembling the windows driver, and some lucky 635 * guesses. Since I do not have any datasheet or other 636 * documentation, inaccuracies are almost guaranteed. 637 * 638 * Some specs for the ARK3116 can be found here: 639 * http://web.archive.org/web/20060318000438/ 640 * www.arkmicro.com/en/products/view.php?id=10 641 * On that page, 2 GPIO pins are mentioned: I assume these are the 642 * OUT1 and OUT2 pins of the UART, so I added support for those 643 * through the MCR. Since the pins are not available on my hardware, 644 * I could not verify this. 645 * Also, it states there is "on-chip hardware flow control". I have 646 * discovered how to enable that. Unfortunately, I do not know how to 647 * enable XON/XOFF (software) flow control, which would need support 648 * from the chip as well to work. Because of the wording on the web 649 * page there is a real possibility the chip simply does not support 650 * software flow control. 651 * 652 * I got my ark3116 as part of a mobile phone adapter cable. On the 653 * PCB, the following numbered contacts are present: 654 * 655 * 1:- +5V 656 * 2:o DTR 657 * 3:i RX 658 * 4:i DCD 659 * 5:o RTS 660 * 6:o TX 661 * 7:i RI 662 * 8:i DSR 663 * 10:- 0V 664 * 11:i CTS 665 * 666 * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that 667 * may be different for the one you have ;-). 668 * 669 * The windows driver limits the registers to 0-F, so I assume there 670 * are actually 16 present on the device. 671 * 672 * On an UART interrupt, 4 bytes of data come in on the interrupt 673 * endpoint. The bytes are 0xe8 IIR LSR MSR. 674 * 675 * The baudrate seems to be generated from the 12MHz crystal, using 676 * 4-times subsampling. So quot=12e6/(4*baud). Also see description 677 * of register E. 678 * 679 * Registers 0-7: 680 * These seem to be the same as for a regular 16450. The FCR is set 681 * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between 682 * the UART and the USB bridge/DMA engine. 683 * 684 * Register 8: 685 * By trial and error, I found out that bit 0 enables hardware CTS, 686 * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making 687 * RTS +5V when the 3116 cannot transfer the data to the USB bus 688 * (verified by disabling the reading URB). Note that as far as I can 689 * tell, the windows driver does NOT use this, so there might be some 690 * hardware bug or something. 691 * 692 * According to a patch provided here 693 * https://lore.kernel.org/lkml/200907261419.50702.linux@rainbow-software.org 694 * the ARK3116 can also be used as an IrDA dongle. Since I do not have 695 * such a thing, I could not investigate that aspect. However, I can 696 * speculate ;-). 697 * 698 * - IrDA encodes data differently than RS232. Most likely, one of 699 * the bits in registers 9..E enables the IR ENDEC (encoder/decoder). 700 * - Depending on the IR transceiver, the input and output need to be 701 * inverted, so there are probably bits for that as well. 702 * - IrDA is half-duplex, so there should be a bit for selecting that. 703 * 704 * This still leaves at least two registers unaccounted for. Perhaps 705 * The chip can do XON/XOFF or CRC in HW? 706 * 707 * Register 9: 708 * Set to 0x00 for IrDA, when the baudrate is initialised. 709 * 710 * Register A: 711 * Set to 0x01 for IrDA, at init. 712 * 713 * Register B: 714 * Set to 0x01 for IrDA, 0x00 for RS232, at init. 715 * 716 * Register C: 717 * Set to 00 for IrDA, at init. 718 * 719 * Register D: 720 * Set to 0x41 for IrDA, at init. 721 * 722 * Register E: 723 * Somekind of baudrate override. The windows driver seems to set 724 * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600. 725 * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer, 726 * it could be somekind of subdivisor thingy. 727 * However,it does not seem to do anything: selecting 921600 (divisor 3, 728 * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would 729 * work, but they don't. 730 * 731 * Register F: unknown 732 */ 733