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 43static const struct usb_device_id id_table[] = { 44 { USB_DEVICE(0x6547, 0x0232) }, 45 { USB_DEVICE(0x18ec, 0x3118) }, /* USB to IrDA adapter */ 46 { }, 47}; 48MODULE_DEVICE_TABLE(usb, id_table); 49 50static 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 59struct 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 77static 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 92static 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 114static 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 124static 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 181static 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 190static 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 296static 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 311static 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 366err_close: 367 usb_serial_generic_close(port); 368err_free: 369 kfree(buf); 370 371 return result; 372} 373 374static 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 400static 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 436static int 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 int ret; 441 442 /* LCR is also used for other things: protect access */ 443 mutex_lock(&priv->hw_lock); 444 445 if (break_state) 446 priv->lcr |= UART_LCR_SBC; 447 else 448 priv->lcr &= ~UART_LCR_SBC; 449 450 ret = ark3116_write_reg(port->serial, UART_LCR, priv->lcr); 451 452 mutex_unlock(&priv->hw_lock); 453 454 return ret; 455} 456 457static void ark3116_update_msr(struct usb_serial_port *port, __u8 msr) 458{ 459 struct ark3116_private *priv = usb_get_serial_port_data(port); 460 unsigned long flags; 461 462 spin_lock_irqsave(&priv->status_lock, flags); 463 priv->msr = msr; 464 spin_unlock_irqrestore(&priv->status_lock, flags); 465 466 if (msr & UART_MSR_ANY_DELTA) { 467 /* update input line counters */ 468 if (msr & UART_MSR_DCTS) 469 port->icount.cts++; 470 if (msr & UART_MSR_DDSR) 471 port->icount.dsr++; 472 if (msr & UART_MSR_DDCD) 473 port->icount.dcd++; 474 if (msr & UART_MSR_TERI) 475 port->icount.rng++; 476 wake_up_interruptible(&port->port.delta_msr_wait); 477 } 478} 479 480static void ark3116_update_lsr(struct usb_serial_port *port, __u8 lsr) 481{ 482 struct ark3116_private *priv = usb_get_serial_port_data(port); 483 unsigned long flags; 484 485 spin_lock_irqsave(&priv->status_lock, flags); 486 /* combine bits */ 487 priv->lsr |= lsr; 488 spin_unlock_irqrestore(&priv->status_lock, flags); 489 490 if (lsr&UART_LSR_BRK_ERROR_BITS) { 491 if (lsr & UART_LSR_BI) 492 port->icount.brk++; 493 if (lsr & UART_LSR_FE) 494 port->icount.frame++; 495 if (lsr & UART_LSR_PE) 496 port->icount.parity++; 497 if (lsr & UART_LSR_OE) 498 port->icount.overrun++; 499 } 500} 501 502static void ark3116_read_int_callback(struct urb *urb) 503{ 504 struct usb_serial_port *port = urb->context; 505 int status = urb->status; 506 const __u8 *data = urb->transfer_buffer; 507 int result; 508 509 switch (status) { 510 case -ECONNRESET: 511 case -ENOENT: 512 case -ESHUTDOWN: 513 /* this urb is terminated, clean up */ 514 dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n", 515 __func__, status); 516 return; 517 default: 518 dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n", 519 __func__, status); 520 break; 521 case 0: /* success */ 522 /* discovered this by trail and error... */ 523 if ((urb->actual_length == 4) && (data[0] == 0xe8)) { 524 const __u8 id = data[1]&UART_IIR_ID; 525 dev_dbg(&port->dev, "%s: iir=%02x\n", __func__, data[1]); 526 if (id == UART_IIR_MSI) { 527 dev_dbg(&port->dev, "%s: msr=%02x\n", 528 __func__, data[3]); 529 ark3116_update_msr(port, data[3]); 530 break; 531 } else if (id == UART_IIR_RLSI) { 532 dev_dbg(&port->dev, "%s: lsr=%02x\n", 533 __func__, data[2]); 534 ark3116_update_lsr(port, data[2]); 535 break; 536 } 537 } 538 /* 539 * Not sure what this data meant... 540 */ 541 usb_serial_debug_data(&port->dev, __func__, 542 urb->actual_length, 543 urb->transfer_buffer); 544 break; 545 } 546 547 result = usb_submit_urb(urb, GFP_ATOMIC); 548 if (result) 549 dev_err(&port->dev, "failed to resubmit interrupt urb: %d\n", 550 result); 551} 552 553 554/* Data comes in via the bulk (data) URB, errors/interrupts via the int URB. 555 * This means that we cannot be sure which data byte has an associated error 556 * condition, so we report an error for all data in the next bulk read. 557 * 558 * Actually, there might even be a window between the bulk data leaving the 559 * ark and reading/resetting the lsr in the read_bulk_callback where an 560 * interrupt for the next data block could come in. 561 * Without somekind of ordering on the ark, we would have to report the 562 * error for the next block of data as well... 563 * For now, let's pretend this can't happen. 564 */ 565static void ark3116_process_read_urb(struct urb *urb) 566{ 567 struct usb_serial_port *port = urb->context; 568 struct ark3116_private *priv = usb_get_serial_port_data(port); 569 unsigned char *data = urb->transfer_buffer; 570 char tty_flag = TTY_NORMAL; 571 unsigned long flags; 572 __u32 lsr; 573 574 /* update line status */ 575 spin_lock_irqsave(&priv->status_lock, flags); 576 lsr = priv->lsr; 577 priv->lsr &= ~UART_LSR_BRK_ERROR_BITS; 578 spin_unlock_irqrestore(&priv->status_lock, flags); 579 580 if (!urb->actual_length) 581 return; 582 583 if (lsr & UART_LSR_BRK_ERROR_BITS) { 584 if (lsr & UART_LSR_BI) 585 tty_flag = TTY_BREAK; 586 else if (lsr & UART_LSR_PE) 587 tty_flag = TTY_PARITY; 588 else if (lsr & UART_LSR_FE) 589 tty_flag = TTY_FRAME; 590 591 /* overrun is special, not associated with a char */ 592 if (lsr & UART_LSR_OE) 593 tty_insert_flip_char(&port->port, 0, TTY_OVERRUN); 594 } 595 tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag, 596 urb->actual_length); 597 tty_flip_buffer_push(&port->port); 598} 599 600static struct usb_serial_driver ark3116_device = { 601 .driver = { 602 .owner = THIS_MODULE, 603 .name = "ark3116", 604 }, 605 .id_table = id_table, 606 .num_ports = 1, 607 .num_bulk_in = 1, 608 .num_bulk_out = 1, 609 .num_interrupt_in = 1, 610 .port_probe = ark3116_port_probe, 611 .port_remove = ark3116_port_remove, 612 .set_termios = ark3116_set_termios, 613 .tiocmget = ark3116_tiocmget, 614 .tiocmset = ark3116_tiocmset, 615 .tiocmiwait = usb_serial_generic_tiocmiwait, 616 .get_icount = usb_serial_generic_get_icount, 617 .open = ark3116_open, 618 .close = ark3116_close, 619 .break_ctl = ark3116_break_ctl, 620 .read_int_callback = ark3116_read_int_callback, 621 .process_read_urb = ark3116_process_read_urb, 622}; 623 624static struct usb_serial_driver * const serial_drivers[] = { 625 &ark3116_device, NULL 626}; 627 628module_usb_serial_driver(serial_drivers, id_table); 629 630MODULE_LICENSE("GPL"); 631 632MODULE_AUTHOR(DRIVER_AUTHOR); 633MODULE_DESCRIPTION(DRIVER_DESC); 634 635/* 636 * The following describes what I learned from studying the old 637 * ark3116.c driver, disassembling the windows driver, and some lucky 638 * guesses. Since I do not have any datasheet or other 639 * documentation, inaccuracies are almost guaranteed. 640 * 641 * Some specs for the ARK3116 can be found here: 642 * http://web.archive.org/web/20060318000438/ 643 * www.arkmicro.com/en/products/view.php?id=10 644 * On that page, 2 GPIO pins are mentioned: I assume these are the 645 * OUT1 and OUT2 pins of the UART, so I added support for those 646 * through the MCR. Since the pins are not available on my hardware, 647 * I could not verify this. 648 * Also, it states there is "on-chip hardware flow control". I have 649 * discovered how to enable that. Unfortunately, I do not know how to 650 * enable XON/XOFF (software) flow control, which would need support 651 * from the chip as well to work. Because of the wording on the web 652 * page there is a real possibility the chip simply does not support 653 * software flow control. 654 * 655 * I got my ark3116 as part of a mobile phone adapter cable. On the 656 * PCB, the following numbered contacts are present: 657 * 658 * 1:- +5V 659 * 2:o DTR 660 * 3:i RX 661 * 4:i DCD 662 * 5:o RTS 663 * 6:o TX 664 * 7:i RI 665 * 8:i DSR 666 * 10:- 0V 667 * 11:i CTS 668 * 669 * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that 670 * may be different for the one you have ;-). 671 * 672 * The windows driver limits the registers to 0-F, so I assume there 673 * are actually 16 present on the device. 674 * 675 * On an UART interrupt, 4 bytes of data come in on the interrupt 676 * endpoint. The bytes are 0xe8 IIR LSR MSR. 677 * 678 * The baudrate seems to be generated from the 12MHz crystal, using 679 * 4-times subsampling. So quot=12e6/(4*baud). Also see description 680 * of register E. 681 * 682 * Registers 0-7: 683 * These seem to be the same as for a regular 16450. The FCR is set 684 * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between 685 * the UART and the USB bridge/DMA engine. 686 * 687 * Register 8: 688 * By trial and error, I found out that bit 0 enables hardware CTS, 689 * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making 690 * RTS +5V when the 3116 cannot transfer the data to the USB bus 691 * (verified by disabling the reading URB). Note that as far as I can 692 * tell, the windows driver does NOT use this, so there might be some 693 * hardware bug or something. 694 * 695 * According to a patch provided here 696 * https://lore.kernel.org/lkml/200907261419.50702.linux@rainbow-software.org 697 * the ARK3116 can also be used as an IrDA dongle. Since I do not have 698 * such a thing, I could not investigate that aspect. However, I can 699 * speculate ;-). 700 * 701 * - IrDA encodes data differently than RS232. Most likely, one of 702 * the bits in registers 9..E enables the IR ENDEC (encoder/decoder). 703 * - Depending on the IR transceiver, the input and output need to be 704 * inverted, so there are probably bits for that as well. 705 * - IrDA is half-duplex, so there should be a bit for selecting that. 706 * 707 * This still leaves at least two registers unaccounted for. Perhaps 708 * The chip can do XON/XOFF or CRC in HW? 709 * 710 * Register 9: 711 * Set to 0x00 for IrDA, when the baudrate is initialised. 712 * 713 * Register A: 714 * Set to 0x01 for IrDA, at init. 715 * 716 * Register B: 717 * Set to 0x01 for IrDA, 0x00 for RS232, at init. 718 * 719 * Register C: 720 * Set to 00 for IrDA, at init. 721 * 722 * Register D: 723 * Set to 0x41 for IrDA, at init. 724 * 725 * Register E: 726 * Somekind of baudrate override. The windows driver seems to set 727 * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600. 728 * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer, 729 * it could be somekind of subdivisor thingy. 730 * However,it does not seem to do anything: selecting 921600 (divisor 3, 731 * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would 732 * work, but they don't. 733 * 734 * Register F: unknown 735 */ 736