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 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 #ifdef CMSPAR 212 if (cflag & CMSPAR) 213 lcr |= UART_LCR_SPAR; 214 #endif 215 /* handshake control */ 216 hcr = (cflag & CRTSCTS) ? 0x03 : 0x00; 217 218 /* calc baudrate */ 219 dev_dbg(&port->dev, "%s - setting bps to %d\n", __func__, bps); 220 eval = 0; 221 switch (bps) { 222 case 0: 223 quot = calc_divisor(9600); 224 break; 225 default: 226 if ((bps < 75) || (bps > 3000000)) 227 bps = 9600; 228 quot = calc_divisor(bps); 229 break; 230 case 460800: 231 eval = 1; 232 quot = calc_divisor(bps); 233 break; 234 case 921600: 235 eval = 2; 236 quot = calc_divisor(bps); 237 break; 238 } 239 240 /* Update state: synchronize */ 241 mutex_lock(&priv->hw_lock); 242 243 /* keep old LCR_SBC bit */ 244 lcr |= (priv->lcr & UART_LCR_SBC); 245 246 dev_dbg(&port->dev, "%s - setting hcr:0x%02x,lcr:0x%02x,quot:%d\n", 247 __func__, hcr, lcr, quot); 248 249 /* handshake control */ 250 if (priv->hcr != hcr) { 251 priv->hcr = hcr; 252 ark3116_write_reg(serial, 0x8, hcr); 253 } 254 255 /* baudrate */ 256 if (priv->quot != quot) { 257 priv->quot = quot; 258 priv->lcr = lcr; /* need to write lcr anyway */ 259 260 /* disable DMA since transmit/receive is 261 * shadowed by UART_DLL 262 */ 263 ark3116_write_reg(serial, UART_FCR, 0); 264 265 ark3116_write_reg(serial, UART_LCR, 266 lcr|UART_LCR_DLAB); 267 ark3116_write_reg(serial, UART_DLL, quot & 0xff); 268 ark3116_write_reg(serial, UART_DLM, (quot>>8) & 0xff); 269 270 /* restore lcr */ 271 ark3116_write_reg(serial, UART_LCR, lcr); 272 /* magic baudrate thingy: not sure what it does, 273 * but windows does this as well. 274 */ 275 ark3116_write_reg(serial, 0xe, eval); 276 277 /* enable DMA */ 278 ark3116_write_reg(serial, UART_FCR, UART_FCR_DMA_SELECT); 279 } else if (priv->lcr != lcr) { 280 priv->lcr = lcr; 281 ark3116_write_reg(serial, UART_LCR, lcr); 282 } 283 284 mutex_unlock(&priv->hw_lock); 285 286 /* check for software flow control */ 287 if (I_IXOFF(tty) || I_IXON(tty)) { 288 dev_warn(&port->dev, 289 "software flow control not implemented\n"); 290 } 291 292 /* Don't rewrite B0 */ 293 if (tty_termios_baud_rate(termios)) 294 tty_termios_encode_baud_rate(termios, bps, bps); 295 } 296 297 static void ark3116_close(struct usb_serial_port *port) 298 { 299 struct usb_serial *serial = port->serial; 300 301 /* disable DMA */ 302 ark3116_write_reg(serial, UART_FCR, 0); 303 304 /* deactivate interrupts */ 305 ark3116_write_reg(serial, UART_IER, 0); 306 307 usb_serial_generic_close(port); 308 309 usb_kill_urb(port->interrupt_in_urb); 310 } 311 312 static int ark3116_open(struct tty_struct *tty, struct usb_serial_port *port) 313 { 314 struct ark3116_private *priv = usb_get_serial_port_data(port); 315 struct usb_serial *serial = port->serial; 316 unsigned char *buf; 317 int result; 318 319 buf = kmalloc(1, GFP_KERNEL); 320 if (buf == NULL) 321 return -ENOMEM; 322 323 result = usb_serial_generic_open(tty, port); 324 if (result) { 325 dev_dbg(&port->dev, 326 "%s - usb_serial_generic_open failed: %d\n", 327 __func__, result); 328 goto err_free; 329 } 330 331 /* remove any data still left: also clears error state */ 332 ark3116_read_reg(serial, UART_RX, buf); 333 334 /* read modem status */ 335 result = ark3116_read_reg(serial, UART_MSR, buf); 336 if (result) 337 goto err_close; 338 priv->msr = *buf; 339 340 /* read line status */ 341 result = ark3116_read_reg(serial, UART_LSR, buf); 342 if (result) 343 goto err_close; 344 priv->lsr = *buf; 345 346 result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL); 347 if (result) { 348 dev_err(&port->dev, "submit irq_in urb failed %d\n", 349 result); 350 goto err_close; 351 } 352 353 /* activate interrupts */ 354 ark3116_write_reg(port->serial, UART_IER, UART_IER_MSI|UART_IER_RLSI); 355 356 /* enable DMA */ 357 ark3116_write_reg(port->serial, UART_FCR, UART_FCR_DMA_SELECT); 358 359 /* setup termios */ 360 if (tty) 361 ark3116_set_termios(tty, port, NULL); 362 363 kfree(buf); 364 365 return 0; 366 367 err_close: 368 usb_serial_generic_close(port); 369 err_free: 370 kfree(buf); 371 372 return result; 373 } 374 375 static int ark3116_tiocmget(struct tty_struct *tty) 376 { 377 struct usb_serial_port *port = tty->driver_data; 378 struct ark3116_private *priv = usb_get_serial_port_data(port); 379 __u32 status; 380 __u32 ctrl; 381 unsigned long flags; 382 383 mutex_lock(&priv->hw_lock); 384 ctrl = priv->mcr; 385 mutex_unlock(&priv->hw_lock); 386 387 spin_lock_irqsave(&priv->status_lock, flags); 388 status = priv->msr; 389 spin_unlock_irqrestore(&priv->status_lock, flags); 390 391 return (status & UART_MSR_DSR ? TIOCM_DSR : 0) | 392 (status & UART_MSR_CTS ? TIOCM_CTS : 0) | 393 (status & UART_MSR_RI ? TIOCM_RI : 0) | 394 (status & UART_MSR_DCD ? TIOCM_CD : 0) | 395 (ctrl & UART_MCR_DTR ? TIOCM_DTR : 0) | 396 (ctrl & UART_MCR_RTS ? TIOCM_RTS : 0) | 397 (ctrl & UART_MCR_OUT1 ? TIOCM_OUT1 : 0) | 398 (ctrl & UART_MCR_OUT2 ? TIOCM_OUT2 : 0); 399 } 400 401 static int ark3116_tiocmset(struct tty_struct *tty, 402 unsigned set, unsigned clr) 403 { 404 struct usb_serial_port *port = tty->driver_data; 405 struct ark3116_private *priv = usb_get_serial_port_data(port); 406 407 /* we need to take the mutex here, to make sure that the value 408 * in priv->mcr is actually the one that is in the hardware 409 */ 410 411 mutex_lock(&priv->hw_lock); 412 413 if (set & TIOCM_RTS) 414 priv->mcr |= UART_MCR_RTS; 415 if (set & TIOCM_DTR) 416 priv->mcr |= UART_MCR_DTR; 417 if (set & TIOCM_OUT1) 418 priv->mcr |= UART_MCR_OUT1; 419 if (set & TIOCM_OUT2) 420 priv->mcr |= UART_MCR_OUT2; 421 if (clr & TIOCM_RTS) 422 priv->mcr &= ~UART_MCR_RTS; 423 if (clr & TIOCM_DTR) 424 priv->mcr &= ~UART_MCR_DTR; 425 if (clr & TIOCM_OUT1) 426 priv->mcr &= ~UART_MCR_OUT1; 427 if (clr & TIOCM_OUT2) 428 priv->mcr &= ~UART_MCR_OUT2; 429 430 ark3116_write_reg(port->serial, UART_MCR, priv->mcr); 431 432 mutex_unlock(&priv->hw_lock); 433 434 return 0; 435 } 436 437 static void ark3116_break_ctl(struct tty_struct *tty, int break_state) 438 { 439 struct usb_serial_port *port = tty->driver_data; 440 struct ark3116_private *priv = usb_get_serial_port_data(port); 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 ark3116_write_reg(port->serial, UART_LCR, priv->lcr); 451 452 mutex_unlock(&priv->hw_lock); 453 } 454 455 static void ark3116_update_msr(struct usb_serial_port *port, __u8 msr) 456 { 457 struct ark3116_private *priv = usb_get_serial_port_data(port); 458 unsigned long flags; 459 460 spin_lock_irqsave(&priv->status_lock, flags); 461 priv->msr = msr; 462 spin_unlock_irqrestore(&priv->status_lock, flags); 463 464 if (msr & UART_MSR_ANY_DELTA) { 465 /* update input line counters */ 466 if (msr & UART_MSR_DCTS) 467 port->icount.cts++; 468 if (msr & UART_MSR_DDSR) 469 port->icount.dsr++; 470 if (msr & UART_MSR_DDCD) 471 port->icount.dcd++; 472 if (msr & UART_MSR_TERI) 473 port->icount.rng++; 474 wake_up_interruptible(&port->port.delta_msr_wait); 475 } 476 } 477 478 static void ark3116_update_lsr(struct usb_serial_port *port, __u8 lsr) 479 { 480 struct ark3116_private *priv = usb_get_serial_port_data(port); 481 unsigned long flags; 482 483 spin_lock_irqsave(&priv->status_lock, flags); 484 /* combine bits */ 485 priv->lsr |= lsr; 486 spin_unlock_irqrestore(&priv->status_lock, flags); 487 488 if (lsr&UART_LSR_BRK_ERROR_BITS) { 489 if (lsr & UART_LSR_BI) 490 port->icount.brk++; 491 if (lsr & UART_LSR_FE) 492 port->icount.frame++; 493 if (lsr & UART_LSR_PE) 494 port->icount.parity++; 495 if (lsr & UART_LSR_OE) 496 port->icount.overrun++; 497 } 498 } 499 500 static void ark3116_read_int_callback(struct urb *urb) 501 { 502 struct usb_serial_port *port = urb->context; 503 int status = urb->status; 504 const __u8 *data = urb->transfer_buffer; 505 int result; 506 507 switch (status) { 508 case -ECONNRESET: 509 case -ENOENT: 510 case -ESHUTDOWN: 511 /* this urb is terminated, clean up */ 512 dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n", 513 __func__, status); 514 return; 515 default: 516 dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n", 517 __func__, status); 518 break; 519 case 0: /* success */ 520 /* discovered this by trail and error... */ 521 if ((urb->actual_length == 4) && (data[0] == 0xe8)) { 522 const __u8 id = data[1]&UART_IIR_ID; 523 dev_dbg(&port->dev, "%s: iir=%02x\n", __func__, data[1]); 524 if (id == UART_IIR_MSI) { 525 dev_dbg(&port->dev, "%s: msr=%02x\n", 526 __func__, data[3]); 527 ark3116_update_msr(port, data[3]); 528 break; 529 } else if (id == UART_IIR_RLSI) { 530 dev_dbg(&port->dev, "%s: lsr=%02x\n", 531 __func__, data[2]); 532 ark3116_update_lsr(port, data[2]); 533 break; 534 } 535 } 536 /* 537 * Not sure what this data meant... 538 */ 539 usb_serial_debug_data(&port->dev, __func__, 540 urb->actual_length, 541 urb->transfer_buffer); 542 break; 543 } 544 545 result = usb_submit_urb(urb, GFP_ATOMIC); 546 if (result) 547 dev_err(&port->dev, "failed to resubmit interrupt urb: %d\n", 548 result); 549 } 550 551 552 /* Data comes in via the bulk (data) URB, errors/interrupts via the int URB. 553 * This means that we cannot be sure which data byte has an associated error 554 * condition, so we report an error for all data in the next bulk read. 555 * 556 * Actually, there might even be a window between the bulk data leaving the 557 * ark and reading/resetting the lsr in the read_bulk_callback where an 558 * interrupt for the next data block could come in. 559 * Without somekind of ordering on the ark, we would have to report the 560 * error for the next block of data as well... 561 * For now, let's pretend this can't happen. 562 */ 563 static void ark3116_process_read_urb(struct urb *urb) 564 { 565 struct usb_serial_port *port = urb->context; 566 struct ark3116_private *priv = usb_get_serial_port_data(port); 567 unsigned char *data = urb->transfer_buffer; 568 char tty_flag = TTY_NORMAL; 569 unsigned long flags; 570 __u32 lsr; 571 572 /* update line status */ 573 spin_lock_irqsave(&priv->status_lock, flags); 574 lsr = priv->lsr; 575 priv->lsr &= ~UART_LSR_BRK_ERROR_BITS; 576 spin_unlock_irqrestore(&priv->status_lock, flags); 577 578 if (!urb->actual_length) 579 return; 580 581 if (lsr & UART_LSR_BRK_ERROR_BITS) { 582 if (lsr & UART_LSR_BI) 583 tty_flag = TTY_BREAK; 584 else if (lsr & UART_LSR_PE) 585 tty_flag = TTY_PARITY; 586 else if (lsr & UART_LSR_FE) 587 tty_flag = TTY_FRAME; 588 589 /* overrun is special, not associated with a char */ 590 if (lsr & UART_LSR_OE) 591 tty_insert_flip_char(&port->port, 0, TTY_OVERRUN); 592 } 593 tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag, 594 urb->actual_length); 595 tty_flip_buffer_push(&port->port); 596 } 597 598 static struct usb_serial_driver ark3116_device = { 599 .driver = { 600 .owner = THIS_MODULE, 601 .name = "ark3116", 602 }, 603 .id_table = id_table, 604 .num_ports = 1, 605 .num_bulk_in = 1, 606 .num_bulk_out = 1, 607 .num_interrupt_in = 1, 608 .port_probe = ark3116_port_probe, 609 .port_remove = ark3116_port_remove, 610 .set_termios = ark3116_set_termios, 611 .tiocmget = ark3116_tiocmget, 612 .tiocmset = ark3116_tiocmset, 613 .tiocmiwait = usb_serial_generic_tiocmiwait, 614 .get_icount = usb_serial_generic_get_icount, 615 .open = ark3116_open, 616 .close = ark3116_close, 617 .break_ctl = ark3116_break_ctl, 618 .read_int_callback = ark3116_read_int_callback, 619 .process_read_urb = ark3116_process_read_urb, 620 }; 621 622 static struct usb_serial_driver * const serial_drivers[] = { 623 &ark3116_device, NULL 624 }; 625 626 module_usb_serial_driver(serial_drivers, id_table); 627 628 MODULE_LICENSE("GPL"); 629 630 MODULE_AUTHOR(DRIVER_AUTHOR); 631 MODULE_DESCRIPTION(DRIVER_DESC); 632 633 /* 634 * The following describes what I learned from studying the old 635 * ark3116.c driver, disassembling the windows driver, and some lucky 636 * guesses. Since I do not have any datasheet or other 637 * documentation, inaccuracies are almost guaranteed. 638 * 639 * Some specs for the ARK3116 can be found here: 640 * http://web.archive.org/web/20060318000438/ 641 * www.arkmicro.com/en/products/view.php?id=10 642 * On that page, 2 GPIO pins are mentioned: I assume these are the 643 * OUT1 and OUT2 pins of the UART, so I added support for those 644 * through the MCR. Since the pins are not available on my hardware, 645 * I could not verify this. 646 * Also, it states there is "on-chip hardware flow control". I have 647 * discovered how to enable that. Unfortunately, I do not know how to 648 * enable XON/XOFF (software) flow control, which would need support 649 * from the chip as well to work. Because of the wording on the web 650 * page there is a real possibility the chip simply does not support 651 * software flow control. 652 * 653 * I got my ark3116 as part of a mobile phone adapter cable. On the 654 * PCB, the following numbered contacts are present: 655 * 656 * 1:- +5V 657 * 2:o DTR 658 * 3:i RX 659 * 4:i DCD 660 * 5:o RTS 661 * 6:o TX 662 * 7:i RI 663 * 8:i DSR 664 * 10:- 0V 665 * 11:i CTS 666 * 667 * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that 668 * may be different for the one you have ;-). 669 * 670 * The windows driver limits the registers to 0-F, so I assume there 671 * are actually 16 present on the device. 672 * 673 * On an UART interrupt, 4 bytes of data come in on the interrupt 674 * endpoint. The bytes are 0xe8 IIR LSR MSR. 675 * 676 * The baudrate seems to be generated from the 12MHz crystal, using 677 * 4-times subsampling. So quot=12e6/(4*baud). Also see description 678 * of register E. 679 * 680 * Registers 0-7: 681 * These seem to be the same as for a regular 16450. The FCR is set 682 * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between 683 * the UART and the USB bridge/DMA engine. 684 * 685 * Register 8: 686 * By trial and error, I found out that bit 0 enables hardware CTS, 687 * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making 688 * RTS +5V when the 3116 cannot transfer the data to the USB bus 689 * (verified by disabling the reading URB). Note that as far as I can 690 * tell, the windows driver does NOT use this, so there might be some 691 * hardware bug or something. 692 * 693 * According to a patch provided here 694 * https://lore.kernel.org/lkml/200907261419.50702.linux@rainbow-software.org 695 * the ARK3116 can also be used as an IrDA dongle. Since I do not have 696 * such a thing, I could not investigate that aspect. However, I can 697 * speculate ;-). 698 * 699 * - IrDA encodes data differently than RS232. Most likely, one of 700 * the bits in registers 9..E enables the IR ENDEC (encoder/decoder). 701 * - Depending on the IR transceiver, the input and output need to be 702 * inverted, so there are probably bits for that as well. 703 * - IrDA is half-duplex, so there should be a bit for selecting that. 704 * 705 * This still leaves at least two registers unaccounted for. Perhaps 706 * The chip can do XON/XOFF or CRC in HW? 707 * 708 * Register 9: 709 * Set to 0x00 for IrDA, when the baudrate is initialised. 710 * 711 * Register A: 712 * Set to 0x01 for IrDA, at init. 713 * 714 * Register B: 715 * Set to 0x01 for IrDA, 0x00 for RS232, at init. 716 * 717 * Register C: 718 * Set to 00 for IrDA, at init. 719 * 720 * Register D: 721 * Set to 0x41 for IrDA, at init. 722 * 723 * Register E: 724 * Somekind of baudrate override. The windows driver seems to set 725 * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600. 726 * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer, 727 * it could be somekind of subdivisor thingy. 728 * However,it does not seem to do anything: selecting 921600 (divisor 3, 729 * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would 730 * work, but they don't. 731 * 732 * Register F: unknown 733 */ 734