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
is_irda(struct usb_serial * serial)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
ark3116_write_reg(struct usb_serial * serial,unsigned reg,__u8 val)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
ark3116_read_reg(struct usb_serial * serial,unsigned reg,unsigned char * buf)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
calc_divisor(int bps)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
ark3116_port_probe(struct usb_serial_port * port)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
ark3116_port_remove(struct usb_serial_port * port)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
ark3116_set_termios(struct tty_struct * tty,struct usb_serial_port * port,const struct ktermios * old_termios)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
ark3116_close(struct usb_serial_port * port)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
ark3116_open(struct tty_struct * tty,struct usb_serial_port * port)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
ark3116_tiocmget(struct tty_struct * tty)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
ark3116_tiocmset(struct tty_struct * tty,unsigned set,unsigned clr)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
ark3116_break_ctl(struct tty_struct * tty,int break_state)436 static 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
ark3116_update_msr(struct usb_serial_port * port,__u8 msr)457 static 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
ark3116_update_lsr(struct usb_serial_port * port,__u8 lsr)480 static 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
ark3116_read_int_callback(struct urb * urb)502 static 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 */
ark3116_process_read_urb(struct urb * urb)565 static 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
600 static struct usb_serial_driver ark3116_device = {
601 .driver = {
602 .name = "ark3116",
603 },
604 .id_table = id_table,
605 .num_ports = 1,
606 .num_bulk_in = 1,
607 .num_bulk_out = 1,
608 .num_interrupt_in = 1,
609 .port_probe = ark3116_port_probe,
610 .port_remove = ark3116_port_remove,
611 .set_termios = ark3116_set_termios,
612 .tiocmget = ark3116_tiocmget,
613 .tiocmset = ark3116_tiocmset,
614 .tiocmiwait = usb_serial_generic_tiocmiwait,
615 .get_icount = usb_serial_generic_get_icount,
616 .open = ark3116_open,
617 .close = ark3116_close,
618 .break_ctl = ark3116_break_ctl,
619 .read_int_callback = ark3116_read_int_callback,
620 .process_read_urb = ark3116_process_read_urb,
621 };
622
623 static struct usb_serial_driver * const serial_drivers[] = {
624 &ark3116_device, NULL
625 };
626
627 module_usb_serial_driver(serial_drivers, id_table);
628
629 MODULE_LICENSE("GPL");
630
631 MODULE_AUTHOR(DRIVER_AUTHOR);
632 MODULE_DESCRIPTION(DRIVER_DESC);
633
634 /*
635 * The following describes what I learned from studying the old
636 * ark3116.c driver, disassembling the windows driver, and some lucky
637 * guesses. Since I do not have any datasheet or other
638 * documentation, inaccuracies are almost guaranteed.
639 *
640 * Some specs for the ARK3116 can be found here:
641 * http://web.archive.org/web/20060318000438/
642 * www.arkmicro.com/en/products/view.php?id=10
643 * On that page, 2 GPIO pins are mentioned: I assume these are the
644 * OUT1 and OUT2 pins of the UART, so I added support for those
645 * through the MCR. Since the pins are not available on my hardware,
646 * I could not verify this.
647 * Also, it states there is "on-chip hardware flow control". I have
648 * discovered how to enable that. Unfortunately, I do not know how to
649 * enable XON/XOFF (software) flow control, which would need support
650 * from the chip as well to work. Because of the wording on the web
651 * page there is a real possibility the chip simply does not support
652 * software flow control.
653 *
654 * I got my ark3116 as part of a mobile phone adapter cable. On the
655 * PCB, the following numbered contacts are present:
656 *
657 * 1:- +5V
658 * 2:o DTR
659 * 3:i RX
660 * 4:i DCD
661 * 5:o RTS
662 * 6:o TX
663 * 7:i RI
664 * 8:i DSR
665 * 10:- 0V
666 * 11:i CTS
667 *
668 * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that
669 * may be different for the one you have ;-).
670 *
671 * The windows driver limits the registers to 0-F, so I assume there
672 * are actually 16 present on the device.
673 *
674 * On an UART interrupt, 4 bytes of data come in on the interrupt
675 * endpoint. The bytes are 0xe8 IIR LSR MSR.
676 *
677 * The baudrate seems to be generated from the 12MHz crystal, using
678 * 4-times subsampling. So quot=12e6/(4*baud). Also see description
679 * of register E.
680 *
681 * Registers 0-7:
682 * These seem to be the same as for a regular 16450. The FCR is set
683 * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between
684 * the UART and the USB bridge/DMA engine.
685 *
686 * Register 8:
687 * By trial and error, I found out that bit 0 enables hardware CTS,
688 * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making
689 * RTS +5V when the 3116 cannot transfer the data to the USB bus
690 * (verified by disabling the reading URB). Note that as far as I can
691 * tell, the windows driver does NOT use this, so there might be some
692 * hardware bug or something.
693 *
694 * According to a patch provided here
695 * https://lore.kernel.org/lkml/200907261419.50702.linux@rainbow-software.org
696 * the ARK3116 can also be used as an IrDA dongle. Since I do not have
697 * such a thing, I could not investigate that aspect. However, I can
698 * speculate ;-).
699 *
700 * - IrDA encodes data differently than RS232. Most likely, one of
701 * the bits in registers 9..E enables the IR ENDEC (encoder/decoder).
702 * - Depending on the IR transceiver, the input and output need to be
703 * inverted, so there are probably bits for that as well.
704 * - IrDA is half-duplex, so there should be a bit for selecting that.
705 *
706 * This still leaves at least two registers unaccounted for. Perhaps
707 * The chip can do XON/XOFF or CRC in HW?
708 *
709 * Register 9:
710 * Set to 0x00 for IrDA, when the baudrate is initialised.
711 *
712 * Register A:
713 * Set to 0x01 for IrDA, at init.
714 *
715 * Register B:
716 * Set to 0x01 for IrDA, 0x00 for RS232, at init.
717 *
718 * Register C:
719 * Set to 00 for IrDA, at init.
720 *
721 * Register D:
722 * Set to 0x41 for IrDA, at init.
723 *
724 * Register E:
725 * Somekind of baudrate override. The windows driver seems to set
726 * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600.
727 * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer,
728 * it could be somekind of subdivisor thingy.
729 * However,it does not seem to do anything: selecting 921600 (divisor 3,
730 * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would
731 * work, but they don't.
732 *
733 * Register F: unknown
734 */
735