xref: /openbmc/linux/drivers/usb/serial/ark3116.c (revision 6ff58ae1)
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 		.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 
624 static struct usb_serial_driver * const serial_drivers[] = {
625 	&ark3116_device, NULL
626 };
627 
628 module_usb_serial_driver(serial_drivers, id_table);
629 
630 MODULE_LICENSE("GPL");
631 
632 MODULE_AUTHOR(DRIVER_AUTHOR);
633 MODULE_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