summaryrefslogtreecommitdiffstats
path: root/drivers/usb/serial/ch341.c
blob: 28deaaec581f6ef91f252fe99cd6cc99db571080 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2007, Frank A Kingswood <frank@kingswood-consulting.co.uk>
 * Copyright 2007, Werner Cornelius <werner@cornelius-consult.de>
 * Copyright 2009, Boris Hajduk <boris@hajduk.org>
 *
 * ch341.c implements a serial port driver for the Winchiphead CH341.
 *
 * The CH341 device can be used to implement an RS232 asynchronous
 * serial port, an IEEE-1284 parallel printer port or a memory-like
 * interface. In all cases the CH341 supports an I2C interface as well.
 * This driver only supports the asynchronous serial interface.
 */

#include <linux/kernel.h>
#include <linux/tty.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/usb.h>
#include <linux/usb/serial.h>
#include <linux/serial.h>
#include <asm/unaligned.h>

#define DEFAULT_BAUD_RATE 9600
#define DEFAULT_TIMEOUT   1000

/* flags for IO-Bits */
#define CH341_BIT_RTS (1 << 6)
#define CH341_BIT_DTR (1 << 5)

/******************************/
/* interrupt pipe definitions */
/******************************/
/* always 4 interrupt bytes */
/* first irq byte normally 0x08 */
/* second irq byte base 0x7d + below */
/* third irq byte base 0x94 + below */
/* fourth irq byte normally 0xee */

/* second interrupt byte */
#define CH341_MULT_STAT 0x04 /* multiple status since last interrupt event */

/* status returned in third interrupt answer byte, inverted in data
   from irq */
#define CH341_BIT_CTS 0x01
#define CH341_BIT_DSR 0x02
#define CH341_BIT_RI  0x04
#define CH341_BIT_DCD 0x08
#define CH341_BITS_MODEM_STAT 0x0f /* all bits */

/* Break support - the information used to implement this was gleaned from
 * the Net/FreeBSD uchcom.c driver by Takanori Watanabe.  Domo arigato.
 */

#define CH341_REQ_READ_VERSION 0x5F
#define CH341_REQ_WRITE_REG    0x9A
#define CH341_REQ_READ_REG     0x95
#define CH341_REQ_SERIAL_INIT  0xA1
#define CH341_REQ_MODEM_CTRL   0xA4

#define CH341_REG_BREAK        0x05
#define CH341_REG_PRESCALER    0x12
#define CH341_REG_DIVISOR      0x13
#define CH341_REG_LCR          0x18
#define CH341_REG_LCR2         0x25

#define CH341_NBREAK_BITS      0x01

#define CH341_LCR_ENABLE_RX    0x80
#define CH341_LCR_ENABLE_TX    0x40
#define CH341_LCR_MARK_SPACE   0x20
#define CH341_LCR_PAR_EVEN     0x10
#define CH341_LCR_ENABLE_PAR   0x08
#define CH341_LCR_STOP_BITS_2  0x04
#define CH341_LCR_CS8          0x03
#define CH341_LCR_CS7          0x02
#define CH341_LCR_CS6          0x01
#define CH341_LCR_CS5          0x00

#define CH341_QUIRK_LIMITED_PRESCALER	BIT(0)
#define CH341_QUIRK_SIMULATE_BREAK	BIT(1)

static const struct usb_device_id id_table[] = {
	{ USB_DEVICE(0x1a86, 0x5512) },
	{ USB_DEVICE(0x1a86, 0x5523) },
	{ USB_DEVICE(0x1a86, 0x7522) },
	{ USB_DEVICE(0x1a86, 0x7523) },
	{ USB_DEVICE(0x4348, 0x5523) },
	{ },
};
MODULE_DEVICE_TABLE(usb, id_table);

struct ch341_private {
	spinlock_t lock; /* access lock */
	unsigned baud_rate; /* set baud rate */
	u8 mcr;
	u8 msr;
	u8 lcr;
	unsigned long quirks;
	unsigned long break_end;
};

static void ch341_set_termios(struct tty_struct *tty,
			      struct usb_serial_port *port,
			      struct ktermios *old_termios);

static int ch341_control_out(struct usb_device *dev, u8 request,
			     u16 value, u16 index)
{
	int r;

	dev_dbg(&dev->dev, "%s - (%02x,%04x,%04x)\n", __func__,
		request, value, index);

	r = usb_control_msg(dev, usb_sndctrlpipe(dev, 0), request,
			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT,
			    value, index, NULL, 0, DEFAULT_TIMEOUT);
	if (r < 0)
		dev_err(&dev->dev, "failed to send control message: %d\n", r);

	return r;
}

static int ch341_control_in(struct usb_device *dev,
			    u8 request, u16 value, u16 index,
			    char *buf, unsigned bufsize)
{
	int r;

	dev_dbg(&dev->dev, "%s - (%02x,%04x,%04x,%u)\n", __func__,
		request, value, index, bufsize);

	r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), request,
			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
			    value, index, buf, bufsize, DEFAULT_TIMEOUT);
	if (r < (int)bufsize) {
		if (r >= 0) {
			dev_err(&dev->dev,
				"short control message received (%d < %u)\n",
				r, bufsize);
			r = -EIO;
		}

		dev_err(&dev->dev, "failed to receive control message: %d\n",
			r);
		return r;
	}

	return 0;
}

#define CH341_CLKRATE		48000000
#define CH341_CLK_DIV(ps, fact)	(1 << (12 - 3 * (ps) - (fact)))
#define CH341_MIN_RATE(ps)	(CH341_CLKRATE / (CH341_CLK_DIV((ps), 1) * 512))

static const speed_t ch341_min_rates[] = {
	CH341_MIN_RATE(0),
	CH341_MIN_RATE(1),
	CH341_MIN_RATE(2),
	CH341_MIN_RATE(3),
};

/* Supported range is 46 to 3000000 bps. */
#define CH341_MIN_BPS	DIV_ROUND_UP(CH341_CLKRATE, CH341_CLK_DIV(0, 0) * 256)
#define CH341_MAX_BPS	(CH341_CLKRATE / (CH341_CLK_DIV(3, 0) * 2))

/*
 * The device line speed is given by the following equation:
 *
 *	baudrate = 48000000 / (2^(12 - 3 * ps - fact) * div), where
 *
 *		0 <= ps <= 3,
 *		0 <= fact <= 1,
 *		2 <= div <= 256 if fact = 0, or
 *		9 <= div <= 256 if fact = 1
 */
static int ch341_get_divisor(struct ch341_private *priv, speed_t speed)
{
	unsigned int fact, div, clk_div;
	bool force_fact0 = false;
	int ps;

	/*
	 * Clamp to supported range, this makes the (ps < 0) and (div < 2)
	 * sanity checks below redundant.
	 */
	speed = clamp_val(speed, CH341_MIN_BPS, CH341_MAX_BPS);

	/*
	 * Start with highest possible base clock (fact = 1) that will give a
	 * divisor strictly less than 512.
	 */
	fact = 1;
	for (ps = 3; ps >= 0; ps--) {
		if (speed > ch341_min_rates[ps])
			break;
	}

	if (ps < 0)
		return -EINVAL;

	/* Determine corresponding divisor, rounding down. */
	clk_div = CH341_CLK_DIV(ps, fact);
	div = CH341_CLKRATE / (clk_div * speed);

	/* Some devices require a lower base clock if ps < 3. */
	if (ps < 3 && (priv->quirks & CH341_QUIRK_LIMITED_PRESCALER))
		force_fact0 = true;

	/* Halve base clock (fact = 0) if required. */
	if (div < 9 || div > 255 || force_fact0) {
		div /= 2;
		clk_div *= 2;
		fact = 0;
	}

	if (div < 2)
		return -EINVAL;

	/*
	 * Pick next divisor if resulting rate is closer to the requested one,
	 * scale up to avoid rounding errors on low rates.
	 */
	if (16 * CH341_CLKRATE / (clk_div * div) - 16 * speed >=
			16 * speed - 16 * CH341_CLKRATE / (clk_div * (div + 1)))
		div++;

	/*
	 * Prefer lower base clock (fact = 0) if even divisor.
	 *
	 * Note that this makes the receiver more tolerant to errors.
	 */
	if (fact == 1 && div % 2 == 0) {
		div /= 2;
		fact = 0;
	}

	return (0x100 - div) << 8 | fact << 2 | ps;
}

static int ch341_set_baudrate_lcr(struct usb_device *dev,
				  struct ch341_private *priv,
				  speed_t baud_rate, u8 lcr)
{
	int val;
	int r;

	if (!baud_rate)
		return -EINVAL;

	val = ch341_get_divisor(priv, baud_rate);
	if (val < 0)
		return -EINVAL;

	/*
	 * CH341A buffers data until a full endpoint-size packet (32 bytes)
	 * has been received unless bit 7 is set.
	 */
	val |= BIT(7);

	r = ch341_control_out(dev, CH341_REQ_WRITE_REG,
			      CH341_REG_DIVISOR << 8 | CH341_REG_PRESCALER,
			      val);
	if (r)
		return r;

	/*
	 * Chip versions before version 0x30 as read using
	 * CH341_REQ_READ_VERSION used separate registers for line control
	 * (stop bits, parity and word length). Version 0x30 and above use
	 * CH341_REG_LCR only and CH341_REG_LCR2 is always set to zero.
	 */
	r = ch341_control_out(dev, CH341_REQ_WRITE_REG,
			      CH341_REG_LCR2 << 8 | CH341_REG_LCR, lcr);
	if (r)
		return r;

	return r;
}

static int ch341_set_handshake(struct usb_device *dev, u8 control)
{
	return ch341_control_out(dev, CH341_REQ_MODEM_CTRL, ~control, 0);
}

static int ch341_get_status(struct usb_device *dev, struct ch341_private *priv)
{
	const unsigned int size = 2;
	char *buffer;
	int r;
	unsigned long flags;

	buffer = kmalloc(size, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;

	r = ch341_control_in(dev, CH341_REQ_READ_REG, 0x0706, 0, buffer, size);
	if (r < 0)
		goto out;

	spin_lock_irqsave(&priv->lock, flags);
	priv->msr = (~(*buffer)) & CH341_BITS_MODEM_STAT;
	spin_unlock_irqrestore(&priv->lock, flags);

out:	kfree(buffer);
	return r;
}

/* -------------------------------------------------------------------------- */

static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
{
	const unsigned int size = 2;
	char *buffer;
	int r;

	buffer = kmalloc(size, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;

	/* expect two bytes 0x27 0x00 */
	r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
	if (r < 0)
		goto out;
	dev_dbg(&dev->dev, "Chip version: 0x%02x\n", buffer[0]);

	r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
	if (r < 0)
		goto out;

	r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr);
	if (r < 0)
		goto out;

	r = ch341_set_handshake(dev, priv->mcr);

out:	kfree(buffer);
	return r;
}

static int ch341_detect_quirks(struct usb_serial_port *port)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	struct usb_device *udev = port->serial->dev;
	const unsigned int size = 2;
	unsigned long quirks = 0;
	char *buffer;
	int r;

	buffer = kmalloc(size, GFP_KERNEL);
	if (!buffer)
		return -ENOMEM;

	/*
	 * A subset of CH34x devices does not support all features. The
	 * prescaler is limited and there is no support for sending a RS232
	 * break condition. A read failure when trying to set up the latter is
	 * used to detect these devices.
	 */
	r = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0), CH341_REQ_READ_REG,
			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
			    CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT);
	if (r == -EPIPE) {
		dev_info(&port->dev, "break control not supported, using simulated break\n");
		quirks = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK;
		r = 0;
		goto out;
	}

	if (r != size) {
		if (r >= 0)
			r = -EIO;
		dev_err(&port->dev, "failed to read break control: %d\n", r);
		goto out;
	}

	r = 0;
out:
	kfree(buffer);

	if (quirks) {
		dev_dbg(&port->dev, "enabling quirk flags: 0x%02lx\n", quirks);
		priv->quirks |= quirks;
	}

	return r;
}

static int ch341_port_probe(struct usb_serial_port *port)
{
	struct ch341_private *priv;
	int r;

	priv = kzalloc(sizeof(struct ch341_private), GFP_KERNEL);
	if (!priv)
		return -ENOMEM;

	spin_lock_init(&priv->lock);
	priv->baud_rate = DEFAULT_BAUD_RATE;
	/*
	 * Some CH340 devices appear unable to change the initial LCR
	 * settings, so set a sane 8N1 default.
	 */
	priv->lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8;

	r = ch341_configure(port->serial->dev, priv);
	if (r < 0)
		goto error;

	usb_set_serial_port_data(port, priv);

	r = ch341_detect_quirks(port);
	if (r < 0)
		goto error;

	return 0;

error:	kfree(priv);
	return r;
}

static int ch341_port_remove(struct usb_serial_port *port)
{
	struct ch341_private *priv;

	priv = usb_get_serial_port_data(port);
	kfree(priv);

	return 0;
}

static int ch341_carrier_raised(struct usb_serial_port *port)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	if (priv->msr & CH341_BIT_DCD)
		return 1;
	return 0;
}

static void ch341_dtr_rts(struct usb_serial_port *port, int on)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	unsigned long flags;

	/* drop DTR and RTS */
	spin_lock_irqsave(&priv->lock, flags);
	if (on)
		priv->mcr |= CH341_BIT_RTS | CH341_BIT_DTR;
	else
		priv->mcr &= ~(CH341_BIT_RTS | CH341_BIT_DTR);
	spin_unlock_irqrestore(&priv->lock, flags);
	ch341_set_handshake(port->serial->dev, priv->mcr);
}

static void ch341_close(struct usb_serial_port *port)
{
	usb_serial_generic_close(port);
	usb_kill_urb(port->interrupt_in_urb);
}


/* open this device, set default parameters */
static int ch341_open(struct tty_struct *tty, struct usb_serial_port *port)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	int r;

	if (tty)
		ch341_set_termios(tty, port, NULL);

	dev_dbg(&port->dev, "%s - submitting interrupt urb\n", __func__);
	r = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
	if (r) {
		dev_err(&port->dev, "%s - failed to submit interrupt urb: %d\n",
			__func__, r);
		return r;
	}

	r = ch341_get_status(port->serial->dev, priv);
	if (r < 0) {
		dev_err(&port->dev, "failed to read modem status: %d\n", r);
		goto err_kill_interrupt_urb;
	}

	r = usb_serial_generic_open(tty, port);
	if (r)
		goto err_kill_interrupt_urb;

	return 0;

err_kill_interrupt_urb:
	usb_kill_urb(port->interrupt_in_urb);

	return r;
}

/* Old_termios contains the original termios settings and
 * tty->termios contains the new setting to be used.
 */
static void ch341_set_termios(struct tty_struct *tty,
		struct usb_serial_port *port, struct ktermios *old_termios)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	unsigned baud_rate;
	unsigned long flags;
	u8 lcr;
	int r;

	/* redundant changes may cause the chip to lose bytes */
	if (old_termios && !tty_termios_hw_change(&tty->termios, old_termios))
		return;

	baud_rate = tty_get_baud_rate(tty);

	lcr = CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX;

	switch (C_CSIZE(tty)) {
	case CS5:
		lcr |= CH341_LCR_CS5;
		break;
	case CS6:
		lcr |= CH341_LCR_CS6;
		break;
	case CS7:
		lcr |= CH341_LCR_CS7;
		break;
	case CS8:
		lcr |= CH341_LCR_CS8;
		break;
	}

	if (C_PARENB(tty)) {
		lcr |= CH341_LCR_ENABLE_PAR;
		if (C_PARODD(tty) == 0)
			lcr |= CH341_LCR_PAR_EVEN;
		if (C_CMSPAR(tty))
			lcr |= CH341_LCR_MARK_SPACE;
	}

	if (C_CSTOPB(tty))
		lcr |= CH341_LCR_STOP_BITS_2;

	if (baud_rate) {
		priv->baud_rate = baud_rate;

		r = ch341_set_baudrate_lcr(port->serial->dev, priv,
					   priv->baud_rate, lcr);
		if (r < 0 && old_termios) {
			priv->baud_rate = tty_termios_baud_rate(old_termios);
			tty_termios_copy_hw(&tty->termios, old_termios);
		} else if (r == 0) {
			priv->lcr = lcr;
		}
	}

	spin_lock_irqsave(&priv->lock, flags);
	if (C_BAUD(tty) == B0)
		priv->mcr &= ~(CH341_BIT_DTR | CH341_BIT_RTS);
	else if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
		priv->mcr |= (CH341_BIT_DTR | CH341_BIT_RTS);
	spin_unlock_irqrestore(&priv->lock, flags);

	ch341_set_handshake(port->serial->dev, priv->mcr);
}

/*
 * A subset of all CH34x devices don't support a real break condition and
 * reading CH341_REG_BREAK fails (see also ch341_detect_quirks). This function
 * simulates a break condition by lowering the baud rate to the minimum
 * supported by the hardware upon enabling the break condition and sending
 * a NUL byte.
 *
 * Incoming data is corrupted while the break condition is being simulated.
 *
 * Normally the duration of the break condition can be controlled individually
 * by userspace using TIOCSBRK and TIOCCBRK or by passing an argument to
 * TCSBRKP. Due to how the simulation is implemented the duration can't be
 * controlled. The duration is always about (1s / 46bd * 9bit) = 196ms.
 */
static void ch341_simulate_break(struct tty_struct *tty, int break_state)
{
	struct usb_serial_port *port = tty->driver_data;
	struct ch341_private *priv = usb_get_serial_port_data(port);
	unsigned long now, delay;
	int r;

	if (break_state != 0) {
		dev_dbg(&port->dev, "enter break state requested\n");

		r = ch341_set_baudrate_lcr(port->serial->dev, priv,
				CH341_MIN_BPS,
				CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX | CH341_LCR_CS8);
		if (r < 0) {
			dev_err(&port->dev,
				"failed to change baud rate to %u: %d\n",
				CH341_MIN_BPS, r);
			goto restore;
		}

		r = tty_put_char(tty, '\0');
		if (r < 0) {
			dev_err(&port->dev,
				"failed to write NUL byte for simulated break condition: %d\n",
				r);
			goto restore;
		}

		/*
		 * Compute expected transmission duration including safety
		 * margin. The original baud rate is only restored after the
		 * computed point in time.
		 *
		 * 11 bits = 1 start, 8 data, 1 stop, 1 margin
		 */
		priv->break_end = jiffies + (11 * HZ / CH341_MIN_BPS);

		return;
	}

	dev_dbg(&port->dev, "leave break state requested\n");

	now = jiffies;

	if (time_before(now, priv->break_end)) {
		/* Wait until NUL byte is written */
		delay = priv->break_end - now;
		dev_dbg(&port->dev,
			"wait %d ms while transmitting NUL byte at %u baud\n",
			jiffies_to_msecs(delay), CH341_MIN_BPS);
		schedule_timeout_interruptible(delay);
	}

restore:
	/* Restore original baud rate */
	r = ch341_set_baudrate_lcr(port->serial->dev, priv, priv->baud_rate,
				   priv->lcr);
	if (r < 0)
		dev_err(&port->dev,
			"restoring original baud rate of %u failed: %d\n",
			priv->baud_rate, r);
}

static void ch341_break_ctl(struct tty_struct *tty, int break_state)
{
	const uint16_t ch341_break_reg =
			((uint16_t) CH341_REG_LCR << 8) | CH341_REG_BREAK;
	struct usb_serial_port *port = tty->driver_data;
	struct ch341_private *priv = usb_get_serial_port_data(port);
	int r;
	uint16_t reg_contents;
	uint8_t *break_reg;

	if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) {
		ch341_simulate_break(tty, break_state);
		return;
	}

	break_reg = kmalloc(2, GFP_KERNEL);
	if (!break_reg)
		return;

	r = ch341_control_in(port->serial->dev, CH341_REQ_READ_REG,
			ch341_break_reg, 0, break_reg, 2);
	if (r < 0) {
		dev_err(&port->dev, "%s - USB control read error (%d)\n",
				__func__, r);
		goto out;
	}
	dev_dbg(&port->dev, "%s - initial ch341 break register contents - reg1: %x, reg2: %x\n",
		__func__, break_reg[0], break_reg[1]);
	if (break_state != 0) {
		dev_dbg(&port->dev, "%s - Enter break state requested\n", __func__);
		break_reg[0] &= ~CH341_NBREAK_BITS;
		break_reg[1] &= ~CH341_LCR_ENABLE_TX;
	} else {
		dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
		break_reg[0] |= CH341_NBREAK_BITS;
		break_reg[1] |= CH341_LCR_ENABLE_TX;
	}
	dev_dbg(&port->dev, "%s - New ch341 break register contents - reg1: %x, reg2: %x\n",
		__func__, break_reg[0], break_reg[1]);
	reg_contents = get_unaligned_le16(break_reg);
	r = ch341_control_out(port->serial->dev, CH341_REQ_WRITE_REG,
			ch341_break_reg, reg_contents);
	if (r < 0)
		dev_err(&port->dev, "%s - USB control write error (%d)\n",
				__func__, r);
out:
	kfree(break_reg);
}

static int ch341_tiocmset(struct tty_struct *tty,
			  unsigned int set, unsigned int clear)
{
	struct usb_serial_port *port = tty->driver_data;
	struct ch341_private *priv = usb_get_serial_port_data(port);
	unsigned long flags;
	u8 control;

	spin_lock_irqsave(&priv->lock, flags);
	if (set & TIOCM_RTS)
		priv->mcr |= CH341_BIT_RTS;
	if (set & TIOCM_DTR)
		priv->mcr |= CH341_BIT_DTR;
	if (clear & TIOCM_RTS)
		priv->mcr &= ~CH341_BIT_RTS;
	if (clear & TIOCM_DTR)
		priv->mcr &= ~CH341_BIT_DTR;
	control = priv->mcr;
	spin_unlock_irqrestore(&priv->lock, flags);

	return ch341_set_handshake(port->serial->dev, control);
}

static void ch341_update_status(struct usb_serial_port *port,
					unsigned char *data, size_t len)
{
	struct ch341_private *priv = usb_get_serial_port_data(port);
	struct tty_struct *tty;
	unsigned long flags;
	u8 status;
	u8 delta;

	if (len < 4)
		return;

	status = ~data[2] & CH341_BITS_MODEM_STAT;

	spin_lock_irqsave(&priv->lock, flags);
	delta = status ^ priv->msr;
	priv->msr = status;
	spin_unlock_irqrestore(&priv->lock, flags);

	if (data[1] & CH341_MULT_STAT)
		dev_dbg(&port->dev, "%s - multiple status change\n", __func__);

	if (!delta)
		return;

	if (delta & CH341_BIT_CTS)
		port->icount.cts++;
	if (delta & CH341_BIT_DSR)
		port->icount.dsr++;
	if (delta & CH341_BIT_RI)
		port->icount.rng++;
	if (delta & CH341_BIT_DCD) {
		port->icount.dcd++;
		tty = tty_port_tty_get(&port->port);
		if (tty) {
			usb_serial_handle_dcd_change(port, tty,
						status & CH341_BIT_DCD);
			tty_kref_put(tty);
		}
	}

	wake_up_interruptible(&port->port.delta_msr_wait);
}

static void ch341_read_int_callback(struct urb *urb)
{
	struct usb_serial_port *port = urb->context;
	unsigned char *data = urb->transfer_buffer;
	unsigned int len = urb->actual_length;
	int status;

	switch (urb->status) {
	case 0:
		/* success */
		break;
	case -ECONNRESET:
	case -ENOENT:
	case -ESHUTDOWN:
		/* this urb is terminated, clean up */
		dev_dbg(&urb->dev->dev, "%s - urb shutting down: %d\n",
			__func__, urb->status);
		return;
	default:
		dev_dbg(&urb->dev->dev, "%s - nonzero urb status: %d\n",
			__func__, urb->status);
		goto exit;
	}

	usb_serial_debug_data(&port->dev, __func__, len, data);
	ch341_update_status(port, data, len);
exit:
	status = usb_submit_urb(urb, GFP_ATOMIC);
	if (status) {
		dev_err(&urb->dev->dev, "%s - usb_submit_urb failed: %d\n",
			__func__, status);
	}
}

static int ch341_tiocmget(struct tty_struct *tty)
{
	struct usb_serial_port *port = tty->driver_data;
	struct ch341_private *priv = usb_get_serial_port_data(port);
	unsigned long flags;
	u8 mcr;
	u8 status;
	unsigned int result;

	spin_lock_irqsave(&priv->lock, flags);
	mcr = priv->mcr;
	status = priv->msr;
	spin_unlock_irqrestore(&priv->lock, flags);

	result = ((mcr & CH341_BIT_DTR)		? TIOCM_DTR : 0)
		  | ((mcr & CH341_BIT_RTS)	? TIOCM_RTS : 0)
		  | ((status & CH341_BIT_CTS)	? TIOCM_CTS : 0)
		  | ((status & CH341_BIT_DSR)	? TIOCM_DSR : 0)
		  | ((status & CH341_BIT_RI)	? TIOCM_RI  : 0)
		  | ((status & CH341_BIT_DCD)	? TIOCM_CD  : 0);

	dev_dbg(&port->dev, "%s - result = %x\n", __func__, result);

	return result;
}

static int ch341_reset_resume(struct usb_serial *serial)
{
	struct usb_serial_port *port = serial->port[0];
	struct ch341_private *priv;
	int ret;

	priv = usb_get_serial_port_data(port);
	if (!priv)
		return 0;

	/* reconfigure ch341 serial port after bus-reset */
	ch341_configure(serial->dev, priv);

	if (tty_port_initialized(&port->port)) {
		ret = usb_submit_urb(port->interrupt_in_urb, GFP_NOIO);
		if (ret) {
			dev_err(&port->dev, "failed to submit interrupt urb: %d\n",
				ret);
			return ret;
		}

		ret = ch341_get_status(port->serial->dev, priv);
		if (ret < 0) {
			dev_err(&port->dev, "failed to read modem status: %d\n",
				ret);
		}
	}

	return usb_serial_generic_resume(serial);
}

static struct usb_serial_driver ch341_device = {
	.driver = {
		.owner	= THIS_MODULE,
		.name	= "ch341-uart",
	},
	.id_table          = id_table,
	.num_ports         = 1,
	.open              = ch341_open,
	.dtr_rts	   = ch341_dtr_rts,
	.carrier_raised	   = ch341_carrier_raised,
	.close             = ch341_close,
	.set_termios       = ch341_set_termios,
	.break_ctl         = ch341_break_ctl,
	.tiocmget          = ch341_tiocmget,
	.tiocmset          = ch341_tiocmset,
	.tiocmiwait        = usb_serial_generic_tiocmiwait,
	.read_int_callback = ch341_read_int_callback,
	.port_probe        = ch341_port_probe,
	.port_remove       = ch341_port_remove,
	.reset_resume      = ch341_reset_resume,
};

static struct usb_serial_driver * const serial_drivers[] = {
	&ch341_device, NULL
};

module_usb_serial_driver(serial_drivers, id_table);

MODULE_LICENSE("GPL v2");