summaryrefslogtreecommitdiff
path: root/drivers/usb/gadget/u_serial.c
blob: 380a87f6e56c326cb0b1fc74cf4b994af7901632 (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
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
/*
 * u_serial.c - utilities for USB gadget "serial port"/TTY support
 *
 * Copyright (C) 2003 Al Borchers (alborchers@steinerpoint.com)
 * Copyright (C) 2008 David Brownell
 * Copyright (C) 2008 by Nokia Corporation
 *
 * This code also borrows from usbserial.c, which is
 * Copyright (C) 1999 - 2002 Greg Kroah-Hartman (greg@kroah.com)
 * Copyright (C) 2000 Peter Berger (pberger@brimson.com)
 * Copyright (C) 2000 Al Borchers (alborchers@steinerpoint.com)
 *
 * This software is distributed under the terms of the GNU General
 * Public License ("GPL") as published by the Free Software Foundation,
 * either version 2 of that License or (at your option) any later version.
 */

/* #define VERBOSE_DEBUG */

#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/interrupt.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/slab.h>
#include <linux/export.h>

#include "u_serial.h"


/*
 * This component encapsulates the TTY layer glue needed to provide basic
 * "serial port" functionality through the USB gadget stack.  Each such
 * port is exposed through a /dev/ttyGS* node.
 *
 * After initialization (gserial_setup), these TTY port devices stay
 * available until they are removed (gserial_cleanup).  Each one may be
 * connected to a USB function (gserial_connect), or disconnected (with
 * gserial_disconnect) when the USB host issues a config change event.
 * Data can only flow when the port is connected to the host.
 *
 * A given TTY port can be made available in multiple configurations.
 * For example, each one might expose a ttyGS0 node which provides a
 * login application.  In one case that might use CDC ACM interface 0,
 * while another configuration might use interface 3 for that.  The
 * work to handle that (including descriptor management) is not part
 * of this component.
 *
 * Configurations may expose more than one TTY port.  For example, if
 * ttyGS0 provides login service, then ttyGS1 might provide dialer access
 * for a telephone or fax link.  And ttyGS2 might be something that just
 * needs a simple byte stream interface for some messaging protocol that
 * is managed in userspace ... OBEX, PTP, and MTP have been mentioned.
 */

#define PREFIX	"ttyGS"

/*
 * gserial is the lifecycle interface, used by USB functions
 * gs_port is the I/O nexus, used by the tty driver
 * tty_struct links to the tty/filesystem framework
 *
 * gserial <---> gs_port ... links will be null when the USB link is
 * inactive; managed by gserial_{connect,disconnect}().  each gserial
 * instance can wrap its own USB control protocol.
 *	gserial->ioport == usb_ep->driver_data ... gs_port
 *	gs_port->port_usb ... gserial
 *
 * gs_port <---> tty_struct ... links will be null when the TTY file
 * isn't opened; managed by gs_open()/gs_close()
 *	gserial->port_tty ... tty_struct
 *	tty_struct->driver_data ... gserial
 */

/* RX and TX queues can buffer QUEUE_SIZE packets before they hit the
 * next layer of buffering.  For TX that's a circular buffer; for RX
 * consider it a NOP.  A third layer is provided by the TTY code.
 */
#define QUEUE_SIZE		16
#define WRITE_BUF_SIZE		8192		/* TX only */

/* circular buffer */
struct gs_buf {
	unsigned		buf_size;
	char			*buf_buf;
	char			*buf_get;
	char			*buf_put;
};

/*
 * The port structure holds info for each port, one for each minor number
 * (and thus for each /dev/ node).
 */
struct gs_port {
	spinlock_t		port_lock;	/* guard port_* access */

	struct gserial		*port_usb;
	struct tty_struct	*port_tty;

	unsigned		open_count;
	bool			openclose;	/* open/close in progress */
	u8			port_num;

	wait_queue_head_t	close_wait;	/* wait for last close */

	struct list_head	read_pool;
	int read_started;
	int read_allocated;
	struct list_head	read_queue;
	unsigned		n_read;
	struct tasklet_struct	push;

	struct list_head	write_pool;
	int write_started;
	int write_allocated;
	struct gs_buf		port_write_buf;
	wait_queue_head_t	drain_wait;	/* wait while writes drain */

	/* REVISIT this state ... */
	struct usb_cdc_line_coding port_line_coding;	/* 8-N-1 etc */
};

/* increase N_PORTS if you need more */
#define N_PORTS		4
static struct portmaster {
	struct mutex	lock;			/* protect open/close */
	struct gs_port	*port;
} ports[N_PORTS];
static unsigned	n_ports;

#define GS_CLOSE_TIMEOUT		15		/* seconds */



#ifdef VERBOSE_DEBUG
#define pr_vdebug(fmt, arg...) \
	pr_debug(fmt, ##arg)
#else
#define pr_vdebug(fmt, arg...) \
	({ if (0) pr_debug(fmt, ##arg); })
#endif

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

/* Circular Buffer */

/*
 * gs_buf_alloc
 *
 * Allocate a circular buffer and all associated memory.
 */
static int gs_buf_alloc(struct gs_buf *gb, unsigned size)
{
	gb->buf_buf = kmalloc(size, GFP_KERNEL);
	if (gb->buf_buf == NULL)
		return -ENOMEM;

	gb->buf_size = size;
	gb->buf_put = gb->buf_buf;
	gb->buf_get = gb->buf_buf;

	return 0;
}

/*
 * gs_buf_free
 *
 * Free the buffer and all associated memory.
 */
static void gs_buf_free(struct gs_buf *gb)
{
	kfree(gb->buf_buf);
	gb->buf_buf = NULL;
}

/*
 * gs_buf_clear
 *
 * Clear out all data in the circular buffer.
 */
static void gs_buf_clear(struct gs_buf *gb)
{
	gb->buf_get = gb->buf_put;
	/* equivalent to a get of all data available */
}

/*
 * gs_buf_data_avail
 *
 * Return the number of bytes of data written into the circular
 * buffer.
 */
static unsigned gs_buf_data_avail(struct gs_buf *gb)
{
	return (gb->buf_size + gb->buf_put - gb->buf_get) % gb->buf_size;
}

/*
 * gs_buf_space_avail
 *
 * Return the number of bytes of space available in the circular
 * buffer.
 */
static unsigned gs_buf_space_avail(struct gs_buf *gb)
{
	return (gb->buf_size + gb->buf_get - gb->buf_put - 1) % gb->buf_size;
}

/*
 * gs_buf_put
 *
 * Copy data data from a user buffer and put it into the circular buffer.
 * Restrict to the amount of space available.
 *
 * Return the number of bytes copied.
 */
static unsigned
gs_buf_put(struct gs_buf *gb, const char *buf, unsigned count)
{
	unsigned len;

	len  = gs_buf_space_avail(gb);
	if (count > len)
		count = len;

	if (count == 0)
		return 0;

	len = gb->buf_buf + gb->buf_size - gb->buf_put;
	if (count > len) {
		memcpy(gb->buf_put, buf, len);
		memcpy(gb->buf_buf, buf+len, count - len);
		gb->buf_put = gb->buf_buf + count - len;
	} else {
		memcpy(gb->buf_put, buf, count);
		if (count < len)
			gb->buf_put += count;
		else /* count == len */
			gb->buf_put = gb->buf_buf;
	}

	return count;
}

/*
 * gs_buf_get
 *
 * Get data from the circular buffer and copy to the given buffer.
 * Restrict to the amount of data available.
 *
 * Return the number of bytes copied.
 */
static unsigned
gs_buf_get(struct gs_buf *gb, char *buf, unsigned count)
{
	unsigned len;

	len = gs_buf_data_avail(gb);
	if (count > len)
		count = len;

	if (count == 0)
		return 0;

	len = gb->buf_buf + gb->buf_size - gb->buf_get;
	if (count > len) {
		memcpy(buf, gb->buf_get, len);
		memcpy(buf+len, gb->buf_buf, count - len);
		gb->buf_get = gb->buf_buf + count - len;
	} else {
		memcpy(buf, gb->buf_get, count);
		if (count < len)
			gb->buf_get += count;
		else /* count == len */
			gb->buf_get = gb->buf_buf;
	}

	return count;
}

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

/* I/O glue between TTY (upper) and USB function (lower) driver layers */

/*
 * gs_alloc_req
 *
 * Allocate a usb_request and its buffer.  Returns a pointer to the
 * usb_request or NULL if there is an error.
 */
struct usb_request *
gs_alloc_req(struct usb_ep *ep, unsigned len, gfp_t kmalloc_flags)
{
	struct usb_request *req;

	req = usb_ep_alloc_request(ep, kmalloc_flags);

	if (req != NULL) {
		req->length = len;
		req->buf = kmalloc(len, kmalloc_flags);
		if (req->buf == NULL) {
			usb_ep_free_request(ep, req);
			return NULL;
		}
	}

	return req;
}

/*
 * gs_free_req
 *
 * Free a usb_request and its buffer.
 */
void gs_free_req(struct usb_ep *ep, struct usb_request *req)
{
	kfree(req->buf);
	usb_ep_free_request(ep, req);
}

/*
 * gs_send_packet
 *
 * If there is data to send, a packet is built in the given
 * buffer and the size is returned.  If there is no data to
 * send, 0 is returned.
 *
 * Called with port_lock held.
 */
static unsigned
gs_send_packet(struct gs_port *port, char *packet, unsigned size)
{
	unsigned len;

	len = gs_buf_data_avail(&port->port_write_buf);
	if (len < size)
		size = len;
	if (size != 0)
		size = gs_buf_get(&port->port_write_buf, packet, size);
	return size;
}

/*
 * gs_start_tx
 *
 * This function finds available write requests, calls
 * gs_send_packet to fill these packets with data, and
 * continues until either there are no more write requests
 * available or no more data to send.  This function is
 * run whenever data arrives or write requests are available.
 *
 * Context: caller owns port_lock; port_usb is non-null.
 */
static int gs_start_tx(struct gs_port *port)
/*
__releases(&port->port_lock)
__acquires(&port->port_lock)
*/
{
	struct list_head	*pool = &port->write_pool;
	struct usb_ep		*in = port->port_usb->in;
	int			status = 0;
	bool			do_tty_wake = false;

	while (!list_empty(pool)) {
		struct usb_request	*req;
		int			len;

		if (port->write_started >= QUEUE_SIZE)
			break;

		req = list_entry(pool->next, struct usb_request, list);
		len = gs_send_packet(port, req->buf, in->maxpacket);
		if (len == 0) {
			wake_up_interruptible(&port->drain_wait);
			break;
		}
		do_tty_wake = true;

		req->length = len;
		list_del(&req->list);
		req->zero = (gs_buf_data_avail(&port->port_write_buf) == 0);

		pr_vdebug(PREFIX "%d: tx len=%d, 0x%02x 0x%02x 0x%02x ...\n",
				port->port_num, len, *((u8 *)req->buf),
				*((u8 *)req->buf+1), *((u8 *)req->buf+2));

		/* Drop lock while we call out of driver; completions
		 * could be issued while we do so.  Disconnection may
		 * happen too; maybe immediately before we queue this!
		 *
		 * NOTE that we may keep sending data for a while after
		 * the TTY closed (dev->ioport->port_tty is NULL).
		 */
		spin_unlock(&port->port_lock);
		status = usb_ep_queue(in, req, GFP_ATOMIC);
		spin_lock(&port->port_lock);

		if (status) {
			pr_debug("%s: %s %s err %d\n",
					__func__, "queue", in->name, status);
			list_add(&req->list, pool);
			break;
		}

		port->write_started++;

		/* abort immediately after disconnect */
		if (!port->port_usb)
			break;
	}

	if (do_tty_wake && port->port_tty)
		tty_wakeup(port->port_tty);
	return status;
}

/*
 * Context: caller owns port_lock, and port_usb is set
 */
static unsigned gs_start_rx(struct gs_port *port)
/*
__releases(&port->port_lock)
__acquires(&port->port_lock)
*/
{
	struct list_head	*pool = &port->read_pool;
	struct usb_ep		*out = port->port_usb->out;

	while (!list_empty(pool)) {
		struct usb_request	*req;
		int			status;
		struct tty_struct	*tty;

		/* no more rx if closed */
		tty = port->port_tty;
		if (!tty)
			break;

		if (port->read_started >= QUEUE_SIZE)
			break;

		req = list_entry(pool->next, struct usb_request, list);
		list_del(&req->list);
		req->length = out->maxpacket;

		/* drop lock while we call out; the controller driver
		 * may need to call us back (e.g. for disconnect)
		 */
		spin_unlock(&port->port_lock);
		status = usb_ep_queue(out, req, GFP_ATOMIC);
		spin_lock(&port->port_lock);

		if (status) {
			pr_debug("%s: %s %s err %d\n",
					__func__, "queue", out->name, status);
			list_add(&req->list, pool);
			break;
		}
		port->read_started++;

		/* abort immediately after disconnect */
		if (!port->port_usb)
			break;
	}
	return port->read_started;
}

/*
 * RX tasklet takes data out of the RX queue and hands it up to the TTY
 * layer until it refuses to take any more data (or is throttled back).
 * Then it issues reads for any further data.
 *
 * If the RX queue becomes full enough that no usb_request is queued,
 * the OUT endpoint may begin NAKing as soon as its FIFO fills up.
 * So QUEUE_SIZE packets plus however many the FIFO holds (usually two)
 * can be buffered before the TTY layer's buffers (currently 64 KB).
 */
static void gs_rx_push(unsigned long _port)
{
	struct gs_port		*port = (void *)_port;
	struct tty_struct	*tty;
	struct list_head	*queue = &port->read_queue;
	bool			disconnect = false;
	bool			do_push = false;

	/* hand any queued data to the tty */
	spin_lock_irq(&port->port_lock);
	tty = port->port_tty;
	while (!list_empty(queue)) {
		struct usb_request	*req;

		req = list_first_entry(queue, struct usb_request, list);

		/* discard data if tty was closed */
		if (!tty)
			goto recycle;

		/* leave data queued if tty was rx throttled */
		if (test_bit(TTY_THROTTLED, &tty->flags))
			break;

		switch (req->status) {
		case -ESHUTDOWN:
			disconnect = true;
			pr_vdebug(PREFIX "%d: shutdown\n", port->port_num);
			break;

		default:
			/* presumably a transient fault */
			pr_warning(PREFIX "%d: unexpected RX status %d\n",
					port->port_num, req->status);
			/* FALLTHROUGH */
		case 0:
			/* normal completion */
			break;
		}

		/* push data to (open) tty */
		if (req->actual) {
			char		*packet = req->buf;
			unsigned	size = req->actual;
			unsigned	n;
			int		count;

			/* we may have pushed part of this packet already... */
			n = port->n_read;
			if (n) {
				packet += n;
				size -= n;
			}

			count = tty_insert_flip_string(tty, packet, size);
			if (count)
				do_push = true;
			if (count != size) {
				/* stop pushing; TTY layer can't handle more */
				port->n_read += count;
				pr_vdebug(PREFIX "%d: rx block %d/%d\n",
						port->port_num,
						count, req->actual);
				break;
			}
			port->n_read = 0;
		}
recycle:
		list_move(&req->list, &port->read_pool);
		port->read_started--;
	}

	/* Push from tty to ldisc; without low_latency set this is handled by
	 * a workqueue, so we won't get callbacks and can hold port_lock
	 */
	if (tty && do_push)
		tty_flip_buffer_push(tty);


	/* We want our data queue to become empty ASAP, keeping data
	 * in the tty and ldisc (not here).  If we couldn't push any
	 * this time around, there may be trouble unless there's an
	 * implicit tty_unthrottle() call on its way...
	 *
	 * REVISIT we should probably add a timer to keep the tasklet
	 * from starving ... but it's not clear that case ever happens.
	 */
	if (!list_empty(queue) && tty) {
		if (!test_bit(TTY_THROTTLED, &tty->flags)) {
			if (do_push)
				tasklet_schedule(&port->push);
			else
				pr_warning(PREFIX "%d: RX not scheduled?\n",
					port->port_num);
		}
	}

	/* If we're still connected, refill the USB RX queue. */
	if (!disconnect && port->port_usb)
		gs_start_rx(port);

	spin_unlock_irq(&port->port_lock);
}

static void gs_read_complete(struct usb_ep *ep, struct usb_request *req)
{
	struct gs_port	*port = ep->driver_data;

	/* Queue all received data until the tty layer is ready for it. */
	spin_lock(&port->port_lock);
	list_add_tail(&req->list, &port->read_queue);
	tasklet_schedule(&port->push);
	spin_unlock(&port->port_lock);
}

static void gs_write_complete(struct usb_ep *ep, struct usb_request *req)
{
	struct gs_port	*port = ep->driver_data;

	spin_lock(&port->port_lock);
	list_add(&req->list, &port->write_pool);
	port->write_started--;

	switch (req->status) {
	default:
		/* presumably a transient fault */
		pr_warning("%s: unexpected %s status %d\n",
				__func__, ep->name, req->status);
		/* FALL THROUGH */
	case 0:
		/* normal completion */
		gs_start_tx(port);
		break;

	case -ESHUTDOWN:
		/* disconnect */
		pr_vdebug("%s: %s shutdown\n", __func__, ep->name);
		break;
	}

	spin_unlock(&port->port_lock);
}

static void gs_free_requests(struct usb_ep *ep, struct list_head *head,
							 int *allocated)
{
	struct usb_request	*req;

	while (!list_empty(head)) {
		req = list_entry(head->next, struct usb_request, list);
		list_del(&req->list);
		gs_free_req(ep, req);
		if (allocated)
			(*allocated)--;
	}
}

static int gs_alloc_requests(struct usb_ep *ep, struct list_head *head,
		void (*fn)(struct usb_ep *, struct usb_request *),
		int *allocated)
{
	int			i;
	struct usb_request	*req;
	int n = allocated ? QUEUE_SIZE - *allocated : QUEUE_SIZE;

	/* Pre-allocate up to QUEUE_SIZE transfers, but if we can't
	 * do quite that many this time, don't fail ... we just won't
	 * be as speedy as we might otherwise be.
	 */
	for (i = 0; i < n; i++) {
		req = gs_alloc_req(ep, ep->maxpacket, GFP_ATOMIC);
		if (!req)
			return list_empty(head) ? -ENOMEM : 0;
		req->complete = fn;
		list_add_tail(&req->list, head);
		if (allocated)
			(*allocated)++;
	}
	return 0;
}

/**
 * gs_start_io - start USB I/O streams
 * @dev: encapsulates endpoints to use
 * Context: holding port_lock; port_tty and port_usb are non-null
 *
 * We only start I/O when something is connected to both sides of
 * this port.  If nothing is listening on the host side, we may
 * be pointlessly filling up our TX buffers and FIFO.
 */
static int gs_start_io(struct gs_port *port)
{
	struct list_head	*head = &port->read_pool;
	struct usb_ep		*ep = port->port_usb->out;
	int			status;
	unsigned		started;

	/* Allocate RX and TX I/O buffers.  We can't easily do this much
	 * earlier (with GFP_KERNEL) because the requests are coupled to
	 * endpoints, as are the packet sizes we'll be using.  Different
	 * configurations may use different endpoints with a given port;
	 * and high speed vs full speed changes packet sizes too.
	 */
	status = gs_alloc_requests(ep, head, gs_read_complete,
		&port->read_allocated);
	if (status)
		return status;

	status = gs_alloc_requests(port->port_usb->in, &port->write_pool,
			gs_write_complete, &port->write_allocated);
	if (status) {
		gs_free_requests(ep, head, &port->read_allocated);
		return status;
	}

	/* queue read requests */
	port->n_read = 0;
	started = gs_start_rx(port);

	/* unblock any pending writes into our circular buffer */
	if (started) {
		tty_wakeup(port->port_tty);
	} else {
		gs_free_requests(ep, head, &port->read_allocated);
		gs_free_requests(port->port_usb->in, &port->write_pool,
			&port->write_allocated);
		status = -EIO;
	}

	return status;
}

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

/* TTY Driver */

/*
 * gs_open sets up the link between a gs_port and its associated TTY.
 * That link is broken *only* by TTY close(), and all driver methods
 * know that.
 */
static int gs_open(struct tty_struct *tty, struct file *file)
{
	int		port_num = tty->index;
	struct gs_port	*port;
	int		status;

	do {
		mutex_lock(&ports[port_num].lock);
		port = ports[port_num].port;
		if (!port)
			status = -ENODEV;
		else {
			spin_lock_irq(&port->port_lock);

			/* already open?  Great. */
			if (port->open_count) {
				status = 0;
				port->open_count++;

			/* currently opening/closing? wait ... */
			} else if (port->openclose) {
				status = -EBUSY;

			/* ... else we do the work */
			} else {
				status = -EAGAIN;
				port->openclose = true;
			}
			spin_unlock_irq(&port->port_lock);
		}
		mutex_unlock(&ports[port_num].lock);

		switch (status) {
		default:
			/* fully handled */
			return status;
		case -EAGAIN:
			/* must do the work */
			break;
		case -EBUSY:
			/* wait for EAGAIN task to finish */
			msleep(1);
			/* REVISIT could have a waitchannel here, if
			 * concurrent open performance is important
			 */
			break;
		}
	} while (status != -EAGAIN);

	/* Do the "real open" */
	spin_lock_irq(&port->port_lock);

	/* allocate circular buffer on first open */
	if (port->port_write_buf.buf_buf == NULL) {

		spin_unlock_irq(&port->port_lock);
		status = gs_buf_alloc(&port->port_write_buf, WRITE_BUF_SIZE);
		spin_lock_irq(&port->port_lock);

		if (status) {
			pr_debug("gs_open: ttyGS%d (%p,%p) no buffer\n",
				port->port_num, tty, file);
			port->openclose = false;
			goto exit_unlock_port;
		}
	}

	/* REVISIT if REMOVED (ports[].port NULL), abort the open
	 * to let rmmod work faster (but this way isn't wrong).
	 */

	/* REVISIT maybe wait for "carrier detect" */

	tty->driver_data = port;
	port->port_tty = tty;

	port->open_count = 1;
	port->openclose = false;

	/* if connected, start the I/O stream */
	if (port->port_usb) {
		struct gserial	*gser = port->port_usb;

		pr_debug("gs_open: start ttyGS%d\n", port->port_num);
		gs_start_io(port);

		if (gser->connect)
			gser->connect(gser);
	}

	pr_debug("gs_open: ttyGS%d (%p,%p)\n", port->port_num, tty, file);

	status = 0;

exit_unlock_port:
	spin_unlock_irq(&port->port_lock);
	return status;
}

static int gs_writes_finished(struct gs_port *p)
{
	int cond;

	/* return true on disconnect or empty buffer */
	spin_lock_irq(&p->port_lock);
	cond = (p->port_usb == NULL) || !gs_buf_data_avail(&p->port_write_buf);
	spin_unlock_irq(&p->port_lock);

	return cond;
}

static void gs_close(struct tty_struct *tty, struct file *file)
{
	struct gs_port *port = tty->driver_data;
	struct gserial	*gser;

	spin_lock_irq(&port->port_lock);

	if (port->open_count != 1) {
		if (port->open_count == 0)
			WARN_ON(1);
		else
			--port->open_count;
		goto exit;
	}

	pr_debug("gs_close: ttyGS%d (%p,%p) ...\n", port->port_num, tty, file);

	/* mark port as closing but in use; we can drop port lock
	 * and sleep if necessary
	 */
	port->openclose = true;
	port->open_count = 0;

	gser = port->port_usb;
	if (gser && gser->disconnect)
		gser->disconnect(gser);

	/* wait for circular write buffer to drain, disconnect, or at
	 * most GS_CLOSE_TIMEOUT seconds; then discard the rest
	 */
	if (gs_buf_data_avail(&port->port_write_buf) > 0 && gser) {
		spin_unlock_irq(&port->port_lock);
		wait_event_interruptible_timeout(port->drain_wait,
					gs_writes_finished(port),
					GS_CLOSE_TIMEOUT * HZ);
		spin_lock_irq(&port->port_lock);
		gser = port->port_usb;
	}

	/* Iff we're disconnected, there can be no I/O in flight so it's
	 * ok to free the circular buffer; else just scrub it.  And don't
	 * let the push tasklet fire again until we're re-opened.
	 */
	if (gser == NULL)
		gs_buf_free(&port->port_write_buf);
	else
		gs_buf_clear(&port->port_write_buf);

	tty->driver_data = NULL;
	port->port_tty = NULL;

	port->openclose = false;

	pr_debug("gs_close: ttyGS%d (%p,%p) done!\n",
			port->port_num, tty, file);

	wake_up_interruptible(&port->close_wait);
exit:
	spin_unlock_irq(&port->port_lock);
}

static int gs_write(struct tty_struct *tty, const unsigned char *buf, int count)
{
	struct gs_port	*port = tty->driver_data;
	unsigned long	flags;
	int		status;

	pr_vdebug("gs_write: ttyGS%d (%p) writing %d bytes\n",
			port->port_num, tty, count);

	spin_lock_irqsave(&port->port_lock, flags);
	if (count)
		count = gs_buf_put(&port->port_write_buf, buf, count);
	/* treat count == 0 as flush_chars() */
	if (port->port_usb)
		status = gs_start_tx(port);
	spin_unlock_irqrestore(&port->port_lock, flags);

	return count;
}

static int gs_put_char(struct tty_struct *tty, unsigned char ch)
{
	struct gs_port	*port = tty->driver_data;
	unsigned long	flags;
	int		status;

	pr_vdebug("gs_put_char: (%d,%p) char=0x%x, called from %p\n",
		port->port_num, tty, ch, __builtin_return_address(0));

	spin_lock_irqsave(&port->port_lock, flags);
	status = gs_buf_put(&port->port_write_buf, &ch, 1);
	spin_unlock_irqrestore(&port->port_lock, flags);

	return status;
}

static void gs_flush_chars(struct tty_struct *tty)
{
	struct gs_port	*port = tty->driver_data;
	unsigned long	flags;

	pr_vdebug("gs_flush_chars: (%d,%p)\n", port->port_num, tty);

	spin_lock_irqsave(&port->port_lock, flags);
	if (port->port_usb)
		gs_start_tx(port);
	spin_unlock_irqrestore(&port->port_lock, flags);
}

static int gs_write_room(struct tty_struct *tty)
{
	struct gs_port	*port = tty->driver_data;
	unsigned long	flags;
	int		room = 0;

	spin_lock_irqsave(&port->port_lock, flags);
	if (port->port_usb)
		room = gs_buf_space_avail(&port->port_write_buf);
	spin_unlock_irqrestore(&port->port_lock, flags);

	pr_vdebug("gs_write_room: (%d,%p) room=%d\n",
		port->port_num, tty, room);

	return room;
}

static int gs_chars_in_buffer(struct tty_struct *tty)
{
	struct gs_port	*port = tty->driver_data;
	unsigned long	flags;
	int		chars = 0;

	spin_lock_irqsave(&port->port_lock, flags);
	chars = gs_buf_data_avail(&port->port_write_buf);
	spin_unlock_irqrestore(&port->port_lock, flags);

	pr_vdebug("gs_chars_in_buffer: (%d,%p) chars=%d\n",
		port->port_num, tty, chars);

	return chars;
}

/* undo side effects of setting TTY_THROTTLED */
static void gs_unthrottle(struct tty_struct *tty)
{
	struct gs_port		*port = tty->driver_data;
	unsigned long		flags;

	spin_lock_irqsave(&port->port_lock, flags);
	if (port->port_usb) {
		/* Kickstart read queue processing.  We don't do xon/xoff,
		 * rts/cts, or other handshaking with the host, but if the
		 * read queue backs up enough we'll be NAKing OUT packets.
		 */
		tasklet_schedule(&port->push);
		pr_vdebug(PREFIX "%d: unthrottle\n", port->port_num);
	}
	spin_unlock_irqrestore(&port->port_lock, flags);
}

static int gs_break_ctl(struct tty_struct *tty, int duration)
{
	struct gs_port	*port = tty->driver_data;
	int		status = 0;
	struct gserial	*gser;

	pr_vdebug("gs_break_ctl: ttyGS%d, send break (%d) \n",
			port->port_num, duration);

	spin_lock_irq(&port->port_lock);
	gser = port->port_usb;
	if (gser && gser->send_break)
		status = gser->send_break(gser, duration);
	spin_unlock_irq(&port->port_lock);

	return status;
}

static const struct tty_operations gs_tty_ops = {
	.open =			gs_open,
	.close =		gs_close,
	.write =		gs_write,
	.put_char =		gs_put_char,
	.flush_chars =		gs_flush_chars,
	.write_room =		gs_write_room,
	.chars_in_buffer =	gs_chars_in_buffer,
	.unthrottle =		gs_unthrottle,
	.break_ctl =		gs_break_ctl,
};

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

static struct tty_driver *gs_tty_driver;

static int
gs_port_alloc(unsigned port_num, struct usb_cdc_line_coding *coding)
{
	struct gs_port	*port;

	port = kzalloc(sizeof(struct gs_port), GFP_KERNEL);
	if (port == NULL)
		return -ENOMEM;

	spin_lock_init(&port->port_lock);
	init_waitqueue_head(&port->close_wait);
	init_waitqueue_head(&port->drain_wait);

	tasklet_init(&port->push, gs_rx_push, (unsigned long) port);

	INIT_LIST_HEAD(&port->read_pool);
	INIT_LIST_HEAD(&port->read_queue);
	INIT_LIST_HEAD(&port->write_pool);

	port->port_num = port_num;
	port->port_line_coding = *coding;

	ports[port_num].port = port;

	return 0;
}

/**
 * gserial_setup - initialize TTY driver for one or more ports
 * @g: gadget to associate with these ports
 * @count: how many ports to support
 * Context: may sleep
 *
 * The TTY stack needs to know in advance how many devices it should
 * plan to manage.  Use this call to set up the ports you will be
 * exporting through USB.  Later, connect them to functions based
 * on what configuration is activated by the USB host; and disconnect
 * them as appropriate.
 *
 * An example would be a two-configuration device in which both
 * configurations expose port 0, but through different functions.
 * One configuration could even expose port 1 while the other
 * one doesn't.
 *
 * Returns negative errno or zero.
 */
int gserial_setup(struct usb_gadget *g, unsigned count)
{
	unsigned			i;
	struct usb_cdc_line_coding	coding;
	int				status;

	if (count == 0 || count > N_PORTS)
		return -EINVAL;

	gs_tty_driver = alloc_tty_driver(count);
	if (!gs_tty_driver)
		return -ENOMEM;

	gs_tty_driver->driver_name = "g_serial";
	gs_tty_driver->name = PREFIX;
	/* uses dynamically assigned dev_t values */

	gs_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
	gs_tty_driver->subtype = SERIAL_TYPE_NORMAL;
	gs_tty_driver->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
	gs_tty_driver->init_termios = tty_std_termios;

	/* 9600-8-N-1 ... matches defaults expected by "usbser.sys" on
	 * MS-Windows.  Otherwise, most of these flags shouldn't affect
	 * anything unless we were to actually hook up to a serial line.
	 */
	gs_tty_driver->init_termios.c_cflag =
			B9600 | CS8 | CREAD | HUPCL | CLOCAL;
	gs_tty_driver->init_termios.c_ispeed = 9600;
	gs_tty_driver->init_termios.c_ospeed = 9600;

	coding.dwDTERate = cpu_to_le32(9600);
	coding.bCharFormat = 8;
	coding.bParityType = USB_CDC_NO_PARITY;
	coding.bDataBits = USB_CDC_1_STOP_BITS;

	tty_set_operations(gs_tty_driver, &gs_tty_ops);

	/* make devices be openable */
	for (i = 0; i < count; i++) {
		mutex_init(&ports[i].lock);
		status = gs_port_alloc(i, &coding);
		if (status) {
			count = i;
			goto fail;
		}
	}
	n_ports = count;

	/* export the driver ... */
	status = tty_register_driver(gs_tty_driver);
	if (status) {
		pr_err("%s: cannot register, err %d\n",
				__func__, status);
		goto fail;
	}

	/* ... and sysfs class devices, so mdev/udev make /dev/ttyGS* */
	for (i = 0; i < count; i++) {
		struct device	*tty_dev;

		tty_dev = tty_register_device(gs_tty_driver, i, &g->dev);
		if (IS_ERR(tty_dev))
			pr_warning("%s: no classdev for port %d, err %ld\n",
				__func__, i, PTR_ERR(tty_dev));
	}

	pr_debug("%s: registered %d ttyGS* device%s\n", __func__,
			count, (count == 1) ? "" : "s");

	return status;
fail:
	while (count--)
		kfree(ports[count].port);
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;
	return status;
}

static int gs_closed(struct gs_port *port)
{
	int cond;

	spin_lock_irq(&port->port_lock);
	cond = (port->open_count == 0) && !port->openclose;
	spin_unlock_irq(&port->port_lock);
	return cond;
}

/**
 * gserial_cleanup - remove TTY-over-USB driver and devices
 * Context: may sleep
 *
 * This is called to free all resources allocated by @gserial_setup().
 * Accordingly, it may need to wait until some open /dev/ files have
 * closed.
 *
 * The caller must have issued @gserial_disconnect() for any ports
 * that had previously been connected, so that there is never any
 * I/O pending when it's called.
 */
void gserial_cleanup(void)
{
	unsigned	i;
	struct gs_port	*port;

	if (!gs_tty_driver)
		return;

	/* start sysfs and /dev/ttyGS* node removal */
	for (i = 0; i < n_ports; i++)
		tty_unregister_device(gs_tty_driver, i);

	for (i = 0; i < n_ports; i++) {
		/* prevent new opens */
		mutex_lock(&ports[i].lock);
		port = ports[i].port;
		ports[i].port = NULL;
		mutex_unlock(&ports[i].lock);

		tasklet_kill(&port->push);

		/* wait for old opens to finish */
		wait_event(port->close_wait, gs_closed(port));

		WARN_ON(port->port_usb != NULL);

		kfree(port);
	}
	n_ports = 0;

	tty_unregister_driver(gs_tty_driver);
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;

	pr_debug("%s: cleaned up ttyGS* support\n", __func__);
}

/**
 * gserial_connect - notify TTY I/O glue that USB link is active
 * @gser: the function, set up with endpoints and descriptors
 * @port_num: which port is active
 * Context: any (usually from irq)
 *
 * This is called activate endpoints and let the TTY layer know that
 * the connection is active ... not unlike "carrier detect".  It won't
 * necessarily start I/O queues; unless the TTY is held open by any
 * task, there would be no point.  However, the endpoints will be
 * activated so the USB host can perform I/O, subject to basic USB
 * hardware flow control.
 *
 * Caller needs to have set up the endpoints and USB function in @dev
 * before calling this, as well as the appropriate (speed-specific)
 * endpoint descriptors, and also have set up the TTY driver by calling
 * @gserial_setup().
 *
 * Returns negative errno or zero.
 * On success, ep->driver_data will be overwritten.
 */
int gserial_connect(struct gserial *gser, u8 port_num)
{
	struct gs_port	*port;
	unsigned long	flags;
	int		status;

	if (!gs_tty_driver || port_num >= n_ports)
		return -ENXIO;

	/* we "know" gserial_cleanup() hasn't been called */
	port = ports[port_num].port;

	/* activate the endpoints */
	status = usb_ep_enable(gser->in);
	if (status < 0)
		return status;
	gser->in->driver_data = port;

	status = usb_ep_enable(gser->out);
	if (status < 0)
		goto fail_out;
	gser->out->driver_data = port;

	/* then tell the tty glue that I/O can work */
	spin_lock_irqsave(&port->port_lock, flags);
	gser->ioport = port;
	port->port_usb = gser;

	/* REVISIT unclear how best to handle this state...
	 * we don't really couple it with the Linux TTY.
	 */
	gser->port_line_coding = port->port_line_coding;

	/* REVISIT if waiting on "carrier detect", signal. */

	/* if it's already open, start I/O ... and notify the serial
	 * protocol about open/close status (connect/disconnect).
	 */
	if (port->open_count) {
		pr_debug("gserial_connect: start ttyGS%d\n", port->port_num);
		gs_start_io(port);
		if (gser->connect)
			gser->connect(gser);
	} else {
		if (gser->disconnect)
			gser->disconnect(gser);
	}

	spin_unlock_irqrestore(&port->port_lock, flags);

	return status;

fail_out:
	usb_ep_disable(gser->in);
	gser->in->driver_data = NULL;
	return status;
}

/**
 * gserial_disconnect - notify TTY I/O glue that USB link is inactive
 * @gser: the function, on which gserial_connect() was called
 * Context: any (usually from irq)
 *
 * This is called to deactivate endpoints and let the TTY layer know
 * that the connection went inactive ... not unlike "hangup".
 *
 * On return, the state is as if gserial_connect() had never been called;
 * there is no active USB I/O on these endpoints.
 */
void gserial_disconnect(struct gserial *gser)
{
	struct gs_port	*port = gser->ioport;
	unsigned long	flags;

	if (!port)
		return;

	/* tell the TTY glue not to do I/O here any more */
	spin_lock_irqsave(&port->port_lock, flags);

	/* REVISIT as above: how best to track this? */
	port->port_line_coding = gser->port_line_coding;

	port->port_usb = NULL;
	gser->ioport = NULL;
	if (port->open_count > 0 || port->openclose) {
		wake_up_interruptible(&port->drain_wait);
		if (port->port_tty)
			tty_hangup(port->port_tty);
	}
	spin_unlock_irqrestore(&port->port_lock, flags);

	/* disable endpoints, aborting down any active I/O */
	usb_ep_disable(gser->out);
	gser->out->driver_data = NULL;

	usb_ep_disable(gser->in);
	gser->in->driver_data = NULL;

	/* finally, free any unused/unusable I/O buffers */
	spin_lock_irqsave(&port->port_lock, flags);
	if (port->open_count == 0 && !port->openclose)
		gs_buf_free(&port->port_write_buf);
	gs_free_requests(gser->out, &port->read_pool, NULL);
	gs_free_requests(gser->out, &port->read_queue, NULL);
	gs_free_requests(gser->in, &port->write_pool, NULL);

	port->read_allocated = port->read_started =
		port->write_allocated = port->write_started = 0;

	spin_unlock_irqrestore(&port->port_lock, flags);
}