Free Electrons

Embedded Linux Experts

   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
/*
 * 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 <linux/module.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 this module has been loaded, the individual TTY port can be requested
 * (gserial_alloc_line()) and it will stay available until they are removed
 * (gserial_free_line()). 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.
 *
 *
 * 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 {
	struct tty_port		port;
	spinlock_t		port_lock;	/* guard port_* access */

	struct gserial		*port_usb;

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

	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 */
};

static struct portmaster {
	struct mutex	lock;			/* protect open/close */
	struct gs_port	*port;
} ports[MAX_U_SERIAL_PORTS];

#define GS_CLOSE_TIMEOUT		15		/* seconds */



#ifdef VERBOSE_DEBUG
#ifndef pr_vdebug
#define pr_vdebug(fmt, arg...) \
	pr_debug(fmt, ##arg)
#endif /* pr_vdebug */
#else
#ifndef pr_vdebug
#define pr_vdebug(fmt, arg...) \
	({ if (0) pr_debug(fmt, ##arg); })
#endif /* pr_vdebug */
#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;
}
EXPORT_SYMBOL_GPL(gs_alloc_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);
}
EXPORT_SYMBOL_GPL(gs_free_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("ttyGS%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);

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

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

		default:
			/* presumably a transient fault */
			pr_warn("ttyGS%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(&port->port, packet,
					size);
			if (count)
				do_push = true;
			if (count != size) {
				/* stop pushing; TTY layer can't handle more */
				port->n_read += count;
				pr_vdebug("ttyGS%d: rx block %d/%d\n",
					  port->port_num, count, req->actual);
				break;
			}
			port->n_read = 0;
		}

		list_move(&req->list, &port->read_pool);
		port->read_started--;
	}

	/* Push from tty to ldisc; this is handled by a workqueue,
	 * so we won't get callbacks and can hold port_lock
	 */
	if (do_push)
		tty_flip_buffer_push(&port->port);


	/* 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_warn("ttyGS%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->port.count) {
				status = 0;
				port->port.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->port.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->port.count != 1) {
		if (port->port.count == 0)
			WARN_ON(1);
		else
			--port->port.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->port.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(&port->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 %pf\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("ttyGS%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;
	int		ret = 0;

	mutex_lock(&ports[port_num].lock);
	if (ports[port_num].port) {
		ret = -EBUSY;
		goto out;
	}

	port = kzalloc(sizeof(struct gs_port), GFP_KERNEL);
	if (port == NULL) {
		ret = -ENOMEM;
		goto out;
	}

	tty_port_init(&port->port);
	spin_lock_init(&port->port_lock);
	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;
out:
	mutex_unlock(&ports[port_num].lock);
	return ret;
}

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

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

static void gserial_free_port(struct gs_port *port)
{
	tasklet_kill(&port->push);
	/* wait for old opens to finish */
	wait_event(port->port.close_wait, gs_closed(port));
	WARN_ON(port->port_usb != NULL);
	tty_port_destroy(&port->port);
	kfree(port);
}

void gserial_free_line(unsigned char port_num)
{
	struct gs_port	*port;

	mutex_lock(&ports[port_num].lock);
	if (WARN_ON(!ports[port_num].port)) {
		mutex_unlock(&ports[port_num].lock);
		return;
	}
	port = ports[port_num].port;
	ports[port_num].port = NULL;
	mutex_unlock(&ports[port_num].lock);

	gserial_free_port(port);
	tty_unregister_device(gs_tty_driver, port_num);
}
EXPORT_SYMBOL_GPL(gserial_free_line);

int gserial_alloc_line(unsigned char *line_num)
{
	struct usb_cdc_line_coding	coding;
	struct device			*tty_dev;
	int				ret;
	int				port_num;

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

	for (port_num = 0; port_num < MAX_U_SERIAL_PORTS; port_num++) {
		ret = gs_port_alloc(port_num, &coding);
		if (ret == -EBUSY)
			continue;
		if (ret)
			return ret;
		break;
	}
	if (ret)
		return ret;

	/* ... and sysfs class devices, so mdev/udev make /dev/ttyGS* */

	tty_dev = tty_port_register_device(&ports[port_num].port->port,
			gs_tty_driver, port_num, NULL);
	if (IS_ERR(tty_dev)) {
		struct gs_port	*port;
		pr_err("%s: failed to register tty for port %d, err %ld\n",
				__func__, port_num, PTR_ERR(tty_dev));

		ret = PTR_ERR(tty_dev);
		port = ports[port_num].port;
		ports[port_num].port = NULL;
		gserial_free_port(port);
		goto err;
	}
	*line_num = port_num;
err:
	return ret;
}
EXPORT_SYMBOL_GPL(gserial_alloc_line);

/**
 * 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 allocate @port_num by calling
 * @gserial_alloc_line().
 *
 * 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 (port_num >= MAX_U_SERIAL_PORTS)
		return -ENXIO;

	port = ports[port_num].port;
	if (!port) {
		pr_err("serial line %d not allocated.\n", port_num);
		return -EINVAL;
	}
	if (port->port_usb) {
		pr_err("serial line %d is in use.\n", port_num);
		return -EBUSY;
	}

	/* 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->port.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;
}
EXPORT_SYMBOL_GPL(gserial_connect);
/**
 * 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->port.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->port.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);
}
EXPORT_SYMBOL_GPL(gserial_disconnect);

static int userial_init(void)
{
	unsigned			i;
	int				status;

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

	gs_tty_driver->driver_name = "g_serial";
	gs_tty_driver->name = "ttyGS";
	/* 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;

	tty_set_operations(gs_tty_driver, &gs_tty_ops);
	for (i = 0; i < MAX_U_SERIAL_PORTS; i++)
		mutex_init(&ports[i].lock);

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

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

	return status;
fail:
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;
	return status;
}
module_init(userial_init);

static void userial_cleanup(void)
{
	tty_unregister_driver(gs_tty_driver);
	put_tty_driver(gs_tty_driver);
	gs_tty_driver = NULL;
}
module_exit(userial_cleanup);

MODULE_LICENSE("GPL");