summaryrefslogtreecommitdiffstats
path: root/drivers/tty/hvc/hvcs.c
blob: d23759183b4782485f03db20de7fa57279a41ca7 (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
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
/*
 * IBM eServer Hypervisor Virtual Console Server Device Driver
 * Copyright (C) 2003, 2004 IBM Corp.
 *  Ryan S. Arnold (rsa@us.ibm.com)
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
 *
 * Author(s) :  Ryan S. Arnold <rsa@us.ibm.com>
 *
 * This is the device driver for the IBM Hypervisor Virtual Console Server,
 * "hvcs".  The IBM hvcs provides a tty driver interface to allow Linux
 * user space applications access to the system consoles of logically
 * partitioned operating systems, e.g. Linux, running on the same partitioned
 * Power5 ppc64 system.  Physical hardware consoles per partition are not
 * practical on this hardware so system consoles are accessed by this driver
 * using inter-partition firmware interfaces to virtual terminal devices.
 *
 * A vty is known to the HMC as a "virtual serial server adapter".  It is a
 * virtual terminal device that is created by firmware upon partition creation
 * to act as a partitioned OS's console device.
 *
 * Firmware dynamically (via hotplug) exposes vty-servers to a running ppc64
 * Linux system upon their creation by the HMC or their exposure during boot.
 * The non-user interactive backend of this driver is implemented as a vio
 * device driver so that it can receive notification of vty-server lifetimes
 * after it registers with the vio bus to handle vty-server probe and remove
 * callbacks.
 *
 * Many vty-servers can be configured to connect to one vty, but a vty can
 * only be actively connected to by a single vty-server, in any manner, at one
 * time.  If the HMC is currently hosting the console for a target Linux
 * partition; attempts to open the tty device to the partition's console using
 * the hvcs on any partition will return -EBUSY with every open attempt until
 * the HMC frees the connection between its vty-server and the desired
 * partition's vty device.  Conversely, a vty-server may only be connected to
 * a single vty at one time even though it may have several configured vty
 * partner possibilities.
 *
 * Firmware does not provide notification of vty partner changes to this
 * driver.  This means that an HMC Super Admin may add or remove partner vtys
 * from a vty-server's partner list but the changes will not be signaled to
 * the vty-server.  Firmware only notifies the driver when a vty-server is
 * added or removed from the system.  To compensate for this deficiency, this
 * driver implements a sysfs update attribute which provides a method for
 * rescanning partner information upon a user's request.
 *
 * Each vty-server, prior to being exposed to this driver is reference counted
 * using the 2.6 Linux kernel kref construct.
 *
 * For direction on installation and usage of this driver please reference
 * Documentation/powerpc/hvcs.txt.
 */

#include <linux/device.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kref.h>
#include <linux/kthread.h>
#include <linux/list.h>
#include <linux/major.h>
#include <linux/module.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <asm/hvconsole.h>
#include <asm/hvcserver.h>
#include <asm/uaccess.h>
#include <asm/vio.h>

/*
 * 1.3.0 -> 1.3.1 In hvcs_open memset(..,0x00,..) instead of memset(..,0x3F,00).
 * Removed braces around single statements following conditionals.  Removed '=
 * 0' after static int declarations since these default to zero.  Removed
 * list_for_each_safe() and replaced with list_for_each_entry() in
 * hvcs_get_by_index().  The 'safe' version is un-needed now that the driver is
 * using spinlocks.  Changed spin_lock_irqsave() to spin_lock() when locking
 * hvcs_structs_lock and hvcs_pi_lock since these are not touched in an int
 * handler.  Initialized hvcs_structs_lock and hvcs_pi_lock to
 * SPIN_LOCK_UNLOCKED at declaration time rather than in hvcs_module_init().
 * Added spin_lock around list_del() in destroy_hvcs_struct() to protect the
 * list traversals from a deletion.  Removed '= NULL' from pointer declaration
 * statements since they are initialized NULL by default.  Removed wmb()
 * instances from hvcs_try_write().  They probably aren't needed with locking in
 * place.  Added check and cleanup for hvcs_pi_buff = kmalloc() in
 * hvcs_module_init().  Exposed hvcs_struct.index via a sysfs attribute so that
 * the coupling between /dev/hvcs* and a vty-server can be automatically
 * determined.  Moved kobject_put() in hvcs_open outside of the
 * spin_unlock_irqrestore().
 *
 * 1.3.1 -> 1.3.2 Changed method for determining hvcs_struct->index and had it
 * align with how the tty layer always assigns the lowest index available.  This
 * change resulted in a list of ints that denotes which indexes are available.
 * Device additions and removals use the new hvcs_get_index() and
 * hvcs_return_index() helper functions.  The list is created with
 * hvsc_alloc_index_list() and it is destroyed with hvcs_free_index_list().
 * Without these fixes hotplug vty-server adapter support goes crazy with this
 * driver if the user removes a vty-server adapter.  Moved free_irq() outside of
 * the hvcs_final_close() function in order to get it out of the spinlock.
 * Rearranged hvcs_close().  Cleaned up some printks and did some housekeeping
 * on the changelog.  Removed local CLC_LENGTH and used HVCS_CLC_LENGTH from
 * arch/powerepc/include/asm/hvcserver.h
 *
 * 1.3.2 -> 1.3.3 Replaced yield() in hvcs_close() with tty_wait_until_sent() to
 * prevent possible lockup with realtime scheduling as similarly pointed out by
 * akpm in hvc_console.  Changed resulted in the removal of hvcs_final_close()
 * to reorder cleanup operations and prevent discarding of pending data during
 * an hvcs_close().  Removed spinlock protection of hvcs_struct data members in
 * hvcs_write_room() and hvcs_chars_in_buffer() because they aren't needed.
 */

#define HVCS_DRIVER_VERSION "1.3.3"

MODULE_AUTHOR("Ryan S. Arnold <rsa@us.ibm.com>");
MODULE_DESCRIPTION("IBM hvcs (Hypervisor Virtual Console Server) Driver");
MODULE_LICENSE("GPL");
MODULE_VERSION(HVCS_DRIVER_VERSION);

/*
 * Wait this long per iteration while trying to push buffered data to the
 * hypervisor before allowing the tty to complete a close operation.
 */
#define HVCS_CLOSE_WAIT (HZ/100) /* 1/10 of a second */

/*
 * Since the Linux TTY code does not currently (2-04-2004) support dynamic
 * addition of tty derived devices and we shouldn't allocate thousands of
 * tty_device pointers when the number of vty-server & vty partner connections
 * will most often be much lower than this, we'll arbitrarily allocate
 * HVCS_DEFAULT_SERVER_ADAPTERS tty_structs and cdev's by default when we
 * register the tty_driver. This can be overridden using an insmod parameter.
 */
#define HVCS_DEFAULT_SERVER_ADAPTERS	64

/*
 * The user can't insmod with more than HVCS_MAX_SERVER_ADAPTERS hvcs device
 * nodes as a sanity check.  Theoretically there can be over 1 Billion
 * vty-server & vty partner connections.
 */
#define HVCS_MAX_SERVER_ADAPTERS	1024

/*
 * We let Linux assign us a major number and we start the minors at zero.  There
 * is no intuitive mapping between minor number and the target vty-server
 * adapter except that each new vty-server adapter is always assigned to the
 * smallest minor number available.
 */
#define HVCS_MINOR_START	0

/*
 * The hcall interface involves putting 8 chars into each of two registers.
 * We load up those 2 registers (in arch/powerpc/platforms/pseries/hvconsole.c)
 * by casting char[16] to long[2].  It would work without __ALIGNED__, but a 
 * little (tiny) bit slower because an unaligned load is slower than aligned 
 * load.
 */
#define __ALIGNED__	__attribute__((__aligned__(8)))

/*
 * How much data can firmware send with each hvc_put_chars()?  Maybe this
 * should be moved into an architecture specific area.
 */
#define HVCS_BUFF_LEN	16

/*
 * This is the maximum amount of data we'll let the user send us (hvcs_write) at
 * once in a chunk as a sanity check.
 */
#define HVCS_MAX_FROM_USER	4096

/*
 * Be careful when adding flags to this line discipline.  Don't add anything
 * that will cause echoing or we'll go into recursive loop echoing chars back
 * and forth with the console drivers.
 */
static struct ktermios hvcs_tty_termios = {
	.c_iflag = IGNBRK | IGNPAR,
	.c_oflag = OPOST,
	.c_cflag = B38400 | CS8 | CREAD | HUPCL,
	.c_cc = INIT_C_CC,
	.c_ispeed = 38400,
	.c_ospeed = 38400
};

/*
 * This value is used to take the place of a command line parameter when the
 * module is inserted.  It starts as -1 and stays as such if the user doesn't
 * specify a module insmod parameter.  If they DO specify one then it is set to
 * the value of the integer passed in.
 */
static int hvcs_parm_num_devs = -1;
module_param(hvcs_parm_num_devs, int, 0);

static const char hvcs_driver_name[] = "hvcs";
static const char hvcs_device_node[] = "hvcs";
static const char hvcs_driver_string[]
	= "IBM hvcs (Hypervisor Virtual Console Server) Driver";

/* Status of partner info rescan triggered via sysfs. */
static int hvcs_rescan_status;

static struct tty_driver *hvcs_tty_driver;

/*
 * In order to be somewhat sane this driver always associates the hvcs_struct
 * index element with the numerically equal tty->index.  This means that a
 * hotplugged vty-server adapter will always map to the lowest index valued
 * device node.  If vty-servers were hotplug removed from the system and then
 * new ones added the new vty-server may have the largest slot number of all
 * the vty-server adapters in the partition but it may have the lowest dev node
 * index of all the adapters due to the hole left by the hotplug removed
 * adapter.  There are a set of functions provided to get the lowest index for
 * a new device as well as return the index to the list.  This list is allocated
 * with a number of elements equal to the number of device nodes requested when
 * the module was inserted.
 */
static int *hvcs_index_list;

/*
 * How large is the list?  This is kept for traversal since the list is
 * dynamically created.
 */
static int hvcs_index_count;

/*
 * Used by the khvcsd to pick up I/O operations when the kernel_thread is
 * already awake but potentially shifted to TASK_INTERRUPTIBLE state.
 */
static int hvcs_kicked;

/*
 * Use by the kthread construct for task operations like waking the sleeping
 * thread and stopping the kthread.
 */
static struct task_struct *hvcs_task;

/*
 * We allocate this for the use of all of the hvcs_structs when they fetch
 * partner info.
 */
static unsigned long *hvcs_pi_buff;

/* Only allow one hvcs_struct to use the hvcs_pi_buff at a time. */
static DEFINE_SPINLOCK(hvcs_pi_lock);

/* One vty-server per hvcs_struct */
struct hvcs_struct {
	spinlock_t lock;

	/*
	 * This index identifies this hvcs device as the complement to a
	 * specific tty index.
	 */
	unsigned int index;

	struct tty_struct *tty;
	int open_count;

	/*
	 * Used to tell the driver kernel_thread what operations need to take
	 * place upon this hvcs_struct instance.
	 */
	int todo_mask;

	/*
	 * This buffer is required so that when hvcs_write_room() reports that
	 * it can send HVCS_BUFF_LEN characters that it will buffer the full
	 * HVCS_BUFF_LEN characters if need be.  This is essential for opost
	 * writes since they do not do high level buffering and expect to be
	 * able to send what the driver commits to sending buffering
	 * [e.g. tab to space conversions in n_tty.c opost()].
	 */
	char buffer[HVCS_BUFF_LEN];
	int chars_in_buffer;

	/*
	 * Any variable below the kref is valid before a tty is connected and
	 * stays valid after the tty is disconnected.  These shouldn't be
	 * whacked until the kobject refcount reaches zero though some entries
	 * may be changed via sysfs initiatives.
	 */
	struct kref kref; /* ref count & hvcs_struct lifetime */
	int connected; /* is the vty-server currently connected to a vty? */
	uint32_t p_unit_address; /* partner unit address */
	uint32_t p_partition_ID; /* partner partition ID */
	char p_location_code[HVCS_CLC_LENGTH + 1]; /* CLC + Null Term */
	struct list_head next; /* list management */
	struct vio_dev *vdev;
};

/* Required to back map a kref to its containing object */
#define from_kref(k) container_of(k, struct hvcs_struct, kref)

static LIST_HEAD(hvcs_structs);
static DEFINE_SPINLOCK(hvcs_structs_lock);
static DEFINE_MUTEX(hvcs_init_mutex);

static void hvcs_unthrottle(struct tty_struct *tty);
static void hvcs_throttle(struct tty_struct *tty);
static irqreturn_t hvcs_handle_interrupt(int irq, void *dev_instance);

static int hvcs_write(struct tty_struct *tty,
		const unsigned char *buf, int count);
static int hvcs_write_room(struct tty_struct *tty);
static int hvcs_chars_in_buffer(struct tty_struct *tty);

static int hvcs_has_pi(struct hvcs_struct *hvcsd);
static void hvcs_set_pi(struct hvcs_partner_info *pi,
		struct hvcs_struct *hvcsd);
static int hvcs_get_pi(struct hvcs_struct *hvcsd);
static int hvcs_rescan_devices_list(void);

static int hvcs_partner_connect(struct hvcs_struct *hvcsd);
static void hvcs_partner_free(struct hvcs_struct *hvcsd);

static int hvcs_enable_device(struct hvcs_struct *hvcsd,
		uint32_t unit_address, unsigned int irq, struct vio_dev *dev);

static int hvcs_open(struct tty_struct *tty, struct file *filp);
static void hvcs_close(struct tty_struct *tty, struct file *filp);
static void hvcs_hangup(struct tty_struct * tty);

static int __devinit hvcs_probe(struct vio_dev *dev,
		const struct vio_device_id *id);
static int __devexit hvcs_remove(struct vio_dev *dev);
static int __init hvcs_module_init(void);
static void __exit hvcs_module_exit(void);
static int __devinit hvcs_initialize(void);

#define HVCS_SCHED_READ	0x00000001
#define HVCS_QUICK_READ	0x00000002
#define HVCS_TRY_WRITE	0x00000004
#define HVCS_READ_MASK	(HVCS_SCHED_READ | HVCS_QUICK_READ)

static inline struct hvcs_struct *from_vio_dev(struct vio_dev *viod)
{
	return dev_get_drvdata(&viod->dev);
}
/* The sysfs interface for the driver and devices */

static ssize_t hvcs_partner_vtys_show(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;
	int retval;

	spin_lock_irqsave(&hvcsd->lock, flags);
	retval = sprintf(buf, "%X\n", hvcsd->p_unit_address);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return retval;
}
static DEVICE_ATTR(partner_vtys, S_IRUGO, hvcs_partner_vtys_show, NULL);

static ssize_t hvcs_partner_clcs_show(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;
	int retval;

	spin_lock_irqsave(&hvcsd->lock, flags);
	retval = sprintf(buf, "%s\n", &hvcsd->p_location_code[0]);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return retval;
}
static DEVICE_ATTR(partner_clcs, S_IRUGO, hvcs_partner_clcs_show, NULL);

static ssize_t hvcs_current_vty_store(struct device *dev, struct device_attribute *attr, const char * buf,
		size_t count)
{
	/*
	 * Don't need this feature at the present time because firmware doesn't
	 * yet support multiple partners.
	 */
	printk(KERN_INFO "HVCS: Denied current_vty change: -EPERM.\n");
	return -EPERM;
}

static ssize_t hvcs_current_vty_show(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;
	int retval;

	spin_lock_irqsave(&hvcsd->lock, flags);
	retval = sprintf(buf, "%s\n", &hvcsd->p_location_code[0]);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return retval;
}

static DEVICE_ATTR(current_vty,
	S_IRUGO | S_IWUSR, hvcs_current_vty_show, hvcs_current_vty_store);

static ssize_t hvcs_vterm_state_store(struct device *dev, struct device_attribute *attr, const char *buf,
		size_t count)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;

	/* writing a '0' to this sysfs entry will result in the disconnect. */
	if (simple_strtol(buf, NULL, 0) != 0)
		return -EINVAL;

	spin_lock_irqsave(&hvcsd->lock, flags);

	if (hvcsd->open_count > 0) {
		spin_unlock_irqrestore(&hvcsd->lock, flags);
		printk(KERN_INFO "HVCS: vterm state unchanged.  "
				"The hvcs device node is still in use.\n");
		return -EPERM;
	}

	if (hvcsd->connected == 0) {
		spin_unlock_irqrestore(&hvcsd->lock, flags);
		printk(KERN_INFO "HVCS: vterm state unchanged. The"
				" vty-server is not connected to a vty.\n");
		return -EPERM;
	}

	hvcs_partner_free(hvcsd);
	printk(KERN_INFO "HVCS: Closed vty-server@%X and"
			" partner vty@%X:%d connection.\n",
			hvcsd->vdev->unit_address,
			hvcsd->p_unit_address,
			(uint32_t)hvcsd->p_partition_ID);

	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return count;
}

static ssize_t hvcs_vterm_state_show(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;
	int retval;

	spin_lock_irqsave(&hvcsd->lock, flags);
	retval = sprintf(buf, "%d\n", hvcsd->connected);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return retval;
}
static DEVICE_ATTR(vterm_state, S_IRUGO | S_IWUSR,
		hvcs_vterm_state_show, hvcs_vterm_state_store);

static ssize_t hvcs_index_show(struct device *dev, struct device_attribute *attr, char *buf)
{
	struct vio_dev *viod = to_vio_dev(dev);
	struct hvcs_struct *hvcsd = from_vio_dev(viod);
	unsigned long flags;
	int retval;

	spin_lock_irqsave(&hvcsd->lock, flags);
	retval = sprintf(buf, "%d\n", hvcsd->index);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return retval;
}

static DEVICE_ATTR(index, S_IRUGO, hvcs_index_show, NULL);

static struct attribute *hvcs_attrs[] = {
	&dev_attr_partner_vtys.attr,
	&dev_attr_partner_clcs.attr,
	&dev_attr_current_vty.attr,
	&dev_attr_vterm_state.attr,
	&dev_attr_index.attr,
	NULL,
};

static struct attribute_group hvcs_attr_group = {
	.attrs = hvcs_attrs,
};

static ssize_t hvcs_rescan_show(struct device_driver *ddp, char *buf)
{
	/* A 1 means it is updating, a 0 means it is done updating */
	return snprintf(buf, PAGE_SIZE, "%d\n", hvcs_rescan_status);
}

static ssize_t hvcs_rescan_store(struct device_driver *ddp, const char * buf,
		size_t count)
{
	if ((simple_strtol(buf, NULL, 0) != 1)
		&& (hvcs_rescan_status != 0))
		return -EINVAL;

	hvcs_rescan_status = 1;
	printk(KERN_INFO "HVCS: rescanning partner info for all"
		" vty-servers.\n");
	hvcs_rescan_devices_list();
	hvcs_rescan_status = 0;
	return count;
}

static DRIVER_ATTR(rescan,
	S_IRUGO | S_IWUSR, hvcs_rescan_show, hvcs_rescan_store);

static void hvcs_kick(void)
{
	hvcs_kicked = 1;
	wmb();
	wake_up_process(hvcs_task);
}

static void hvcs_unthrottle(struct tty_struct *tty)
{
	struct hvcs_struct *hvcsd = tty->driver_data;
	unsigned long flags;

	spin_lock_irqsave(&hvcsd->lock, flags);
	hvcsd->todo_mask |= HVCS_SCHED_READ;
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	hvcs_kick();
}

static void hvcs_throttle(struct tty_struct *tty)
{
	struct hvcs_struct *hvcsd = tty->driver_data;
	unsigned long flags;

	spin_lock_irqsave(&hvcsd->lock, flags);
	vio_disable_interrupts(hvcsd->vdev);
	spin_unlock_irqrestore(&hvcsd->lock, flags);
}

/*
 * If the device is being removed we don't have to worry about this interrupt
 * handler taking any further interrupts because they are disabled which means
 * the hvcs_struct will always be valid in this handler.
 */
static irqreturn_t hvcs_handle_interrupt(int irq, void *dev_instance)
{
	struct hvcs_struct *hvcsd = dev_instance;

	spin_lock(&hvcsd->lock);
	vio_disable_interrupts(hvcsd->vdev);
	hvcsd->todo_mask |= HVCS_SCHED_READ;
	spin_unlock(&hvcsd->lock);
	hvcs_kick();

	return IRQ_HANDLED;
}

/* This function must be called with the hvcsd->lock held */
static void hvcs_try_write(struct hvcs_struct *hvcsd)
{
	uint32_t unit_address = hvcsd->vdev->unit_address;
	struct tty_struct *tty = hvcsd->tty;
	int sent;

	if (hvcsd->todo_mask & HVCS_TRY_WRITE) {
		/* won't send partial writes */
		sent = hvc_put_chars(unit_address,
				&hvcsd->buffer[0],
				hvcsd->chars_in_buffer );
		if (sent > 0) {
			hvcsd->chars_in_buffer = 0;
			/* wmb(); */
			hvcsd->todo_mask &= ~(HVCS_TRY_WRITE);
			/* wmb(); */

			/*
			 * We are still obligated to deliver the data to the
			 * hypervisor even if the tty has been closed because
			 * we committed to delivering it.  But don't try to wake
			 * a non-existent tty.
			 */
			if (tty) {
				tty_wakeup(tty);
			}
		}
	}
}

static int hvcs_io(struct hvcs_struct *hvcsd)
{
	uint32_t unit_address;
	struct tty_struct *tty;
	char buf[HVCS_BUFF_LEN] __ALIGNED__;
	unsigned long flags;
	int got = 0;

	spin_lock_irqsave(&hvcsd->lock, flags);

	unit_address = hvcsd->vdev->unit_address;
	tty = hvcsd->tty;

	hvcs_try_write(hvcsd);

	if (!tty || test_bit(TTY_THROTTLED, &tty->flags)) {
		hvcsd->todo_mask &= ~(HVCS_READ_MASK);
		goto bail;
	} else if (!(hvcsd->todo_mask & (HVCS_READ_MASK)))
		goto bail;

	/* remove the read masks */
	hvcsd->todo_mask &= ~(HVCS_READ_MASK);

	if (tty_buffer_request_room(tty, HVCS_BUFF_LEN) >= HVCS_BUFF_LEN) {
		got = hvc_get_chars(unit_address,
				&buf[0],
				HVCS_BUFF_LEN);
		tty_insert_flip_string(tty, buf, got);
	}

	/* Give the TTY time to process the data we just sent. */
	if (got)
		hvcsd->todo_mask |= HVCS_QUICK_READ;

	spin_unlock_irqrestore(&hvcsd->lock, flags);
	/* This is synch because tty->low_latency == 1 */
	if(got)
		tty_flip_buffer_push(tty);

	if (!got) {
		/* Do this _after_ the flip_buffer_push */
		spin_lock_irqsave(&hvcsd->lock, flags);
		vio_enable_interrupts(hvcsd->vdev);
		spin_unlock_irqrestore(&hvcsd->lock, flags);
	}

	return hvcsd->todo_mask;

 bail:
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	return hvcsd->todo_mask;
}

static int khvcsd(void *unused)
{
	struct hvcs_struct *hvcsd;
	int hvcs_todo_mask;

	__set_current_state(TASK_RUNNING);

	do {
		hvcs_todo_mask = 0;
		hvcs_kicked = 0;
		wmb();

		spin_lock(&hvcs_structs_lock);
		list_for_each_entry(hvcsd, &hvcs_structs, next) {
			hvcs_todo_mask |= hvcs_io(hvcsd);
		}
		spin_unlock(&hvcs_structs_lock);

		/*
		 * If any of the hvcs adapters want to try a write or quick read
		 * don't schedule(), yield a smidgen then execute the hvcs_io
		 * thread again for those that want the write.
		 */
		 if (hvcs_todo_mask & (HVCS_TRY_WRITE | HVCS_QUICK_READ)) {
			yield();
			continue;
		}

		set_current_state(TASK_INTERRUPTIBLE);
		if (!hvcs_kicked)
			schedule();
		__set_current_state(TASK_RUNNING);
	} while (!kthread_should_stop());

	return 0;
}

static struct vio_device_id hvcs_driver_table[] __devinitdata= {
	{"serial-server", "hvterm2"},
	{ "", "" }
};
MODULE_DEVICE_TABLE(vio, hvcs_driver_table);

static void hvcs_return_index(int index)
{
	/* Paranoia check */
	if (!hvcs_index_list)
		return;
	if (index < 0 || index >= hvcs_index_count)
		return;
	if (hvcs_index_list[index] == -1)
		return;
	else
		hvcs_index_list[index] = -1;
}

/* callback when the kref ref count reaches zero */
static void destroy_hvcs_struct(struct kref *kref)
{
	struct hvcs_struct *hvcsd = from_kref(kref);
	struct vio_dev *vdev;
	unsigned long flags;

	spin_lock(&hvcs_structs_lock);
	spin_lock_irqsave(&hvcsd->lock, flags);

	/* the list_del poisons the pointers */
	list_del(&(hvcsd->next));

	if (hvcsd->connected == 1) {
		hvcs_partner_free(hvcsd);
		printk(KERN_INFO "HVCS: Closed vty-server@%X and"
				" partner vty@%X:%d connection.\n",
				hvcsd->vdev->unit_address,
				hvcsd->p_unit_address,
				(uint32_t)hvcsd->p_partition_ID);
	}
	printk(KERN_INFO "HVCS: Destroyed hvcs_struct for vty-server@%X.\n",
			hvcsd->vdev->unit_address);

	vdev = hvcsd->vdev;
	hvcsd->vdev = NULL;

	hvcsd->p_unit_address = 0;
	hvcsd->p_partition_ID = 0;
	hvcs_return_index(hvcsd->index);
	memset(&hvcsd->p_location_code[0], 0x00, HVCS_CLC_LENGTH + 1);

	spin_unlock_irqrestore(&hvcsd->lock, flags);
	spin_unlock(&hvcs_structs_lock);

	sysfs_remove_group(&vdev->dev.kobj, &hvcs_attr_group);

	kfree(hvcsd);
}

static int hvcs_get_index(void)
{
	int i;
	/* Paranoia check */
	if (!hvcs_index_list) {
		printk(KERN_ERR "HVCS: hvcs_index_list NOT valid!.\n");
		return -EFAULT;
	}
	/* Find the numerically lowest first free index. */
	for(i = 0; i < hvcs_index_count; i++) {
		if (hvcs_index_list[i] == -1) {
			hvcs_index_list[i] = 0;
			return i;
		}
	}
	return -1;
}

static int __devinit hvcs_probe(
	struct vio_dev *dev,
	const struct vio_device_id *id)
{
	struct hvcs_struct *hvcsd;
	int index, rc;
	int retval;

	if (!dev || !id) {
		printk(KERN_ERR "HVCS: probed with invalid parameter.\n");
		return -EPERM;
	}

	/* Make sure we are properly initialized */
	rc = hvcs_initialize();
	if (rc) {
		pr_err("HVCS: Failed to initialize core driver.\n");
		return rc;
	}

	/* early to avoid cleanup on failure */
	index = hvcs_get_index();
	if (index < 0) {
		return -EFAULT;
	}

	hvcsd = kzalloc(sizeof(*hvcsd), GFP_KERNEL);
	if (!hvcsd)
		return -ENODEV;


	spin_lock_init(&hvcsd->lock);
	/* Automatically incs the refcount the first time */
	kref_init(&hvcsd->kref);

	hvcsd->vdev = dev;
	dev_set_drvdata(&dev->dev, hvcsd);

	hvcsd->index = index;

	/* hvcsd->index = ++hvcs_struct_count; */
	hvcsd->chars_in_buffer = 0;
	hvcsd->todo_mask = 0;
	hvcsd->connected = 0;

	/*
	 * This will populate the hvcs_struct's partner info fields for the
	 * first time.
	 */
	if (hvcs_get_pi(hvcsd)) {
		printk(KERN_ERR "HVCS: Failed to fetch partner"
			" info for vty-server@%X on device probe.\n",
			hvcsd->vdev->unit_address);
	}

	/*
	 * If a user app opens a tty that corresponds to this vty-server before
	 * the hvcs_struct has been added to the devices list then the user app
	 * will get -ENODEV.
	 */
	spin_lock(&hvcs_structs_lock);
	list_add_tail(&(hvcsd->next), &hvcs_structs);
	spin_unlock(&hvcs_structs_lock);

	retval = sysfs_create_group(&dev->dev.kobj, &hvcs_attr_group);
	if (retval) {
		printk(KERN_ERR "HVCS: Can't create sysfs attrs for vty-server@%X\n",
		       hvcsd->vdev->unit_address);
		return retval;
	}

	printk(KERN_INFO "HVCS: vty-server@%X added to the vio bus.\n", dev->unit_address);

	/*
	 * DON'T enable interrupts here because there is no user to receive the
	 * data.
	 */
	return 0;
}

static int __devexit hvcs_remove(struct vio_dev *dev)
{
	struct hvcs_struct *hvcsd = dev_get_drvdata(&dev->dev);
	unsigned long flags;
	struct tty_struct *tty;

	if (!hvcsd)
		return -ENODEV;

	/* By this time the vty-server won't be getting any more interrupts */

	spin_lock_irqsave(&hvcsd->lock, flags);

	tty = hvcsd->tty;

	spin_unlock_irqrestore(&hvcsd->lock, flags);

	/*
	 * Let the last holder of this object cause it to be removed, which
	 * would probably be tty_hangup below.
	 */
	kref_put(&hvcsd->kref, destroy_hvcs_struct);

	/*
	 * The hangup is a scheduled function which will auto chain call
	 * hvcs_hangup.  The tty should always be valid at this time unless a
	 * simultaneous tty close already cleaned up the hvcs_struct.
	 */
	if (tty)
		tty_hangup(tty);

	printk(KERN_INFO "HVCS: vty-server@%X removed from the"
			" vio bus.\n", dev->unit_address);
	return 0;
};

static struct vio_driver hvcs_vio_driver = {
	.id_table	= hvcs_driver_table,
	.probe		= hvcs_probe,
	.remove		= __devexit_p(hvcs_remove),
	.driver		= {
		.name	= hvcs_driver_name,
		.owner	= THIS_MODULE,
	}
};

/* Only called from hvcs_get_pi please */
static void hvcs_set_pi(struct hvcs_partner_info *pi, struct hvcs_struct *hvcsd)
{
	int clclength;

	hvcsd->p_unit_address = pi->unit_address;
	hvcsd->p_partition_ID  = pi->partition_ID;
	clclength = strlen(&pi->location_code[0]);
	if (clclength > HVCS_CLC_LENGTH)
		clclength = HVCS_CLC_LENGTH;

	/* copy the null-term char too */
	strncpy(&hvcsd->p_location_code[0],
			&pi->location_code[0], clclength + 1);
}

/*
 * Traverse the list and add the partner info that is found to the hvcs_struct
 * struct entry. NOTE: At this time I know that partner info will return a
 * single entry but in the future there may be multiple partner info entries per
 * vty-server and you'll want to zero out that list and reset it.  If for some
 * reason you have an old version of this driver but there IS more than one
 * partner info then hvcsd->p_* will hold the last partner info data from the
 * firmware query.  A good way to update this code would be to replace the three
 * partner info fields in hvcs_struct with a list of hvcs_partner_info
 * instances.
 *
 * This function must be called with the hvcsd->lock held.
 */
static int hvcs_get_pi(struct hvcs_struct *hvcsd)
{
	struct hvcs_partner_info *pi;
	uint32_t unit_address = hvcsd->vdev->unit_address;
	struct list_head head;
	int retval;

	spin_lock(&hvcs_pi_lock);
	if (!hvcs_pi_buff) {
		spin_unlock(&hvcs_pi_lock);
		return -EFAULT;
	}
	retval = hvcs_get_partner_info(unit_address, &head, hvcs_pi_buff);
	spin_unlock(&hvcs_pi_lock);
	if (retval) {
		printk(KERN_ERR "HVCS: Failed to fetch partner"
			" info for vty-server@%x.\n", unit_address);
		return retval;
	}

	/* nixes the values if the partner vty went away */
	hvcsd->p_unit_address = 0;
	hvcsd->p_partition_ID = 0;

	list_for_each_entry(pi, &head, node)
		hvcs_set_pi(pi, hvcsd);

	hvcs_free_partner_info(&head);
	return 0;
}

/*
 * This function is executed by the driver "rescan" sysfs entry.  It shouldn't
 * be executed elsewhere, in order to prevent deadlock issues.
 */
static int hvcs_rescan_devices_list(void)
{
	struct hvcs_struct *hvcsd;
	unsigned long flags;

	spin_lock(&hvcs_structs_lock);

	list_for_each_entry(hvcsd, &hvcs_structs, next) {
		spin_lock_irqsave(&hvcsd->lock, flags);
		hvcs_get_pi(hvcsd);
		spin_unlock_irqrestore(&hvcsd->lock, flags);
	}

	spin_unlock(&hvcs_structs_lock);

	return 0;
}

/*
 * Farm this off into its own function because it could be more complex once
 * multiple partners support is added. This function should be called with
 * the hvcsd->lock held.
 */
static int hvcs_has_pi(struct hvcs_struct *hvcsd)
{
	if ((!hvcsd->p_unit_address) || (!hvcsd->p_partition_ID))
		return 0;
	return 1;
}

/*
 * NOTE: It is possible that the super admin removed a partner vty and then
 * added a different vty as the new partner.
 *
 * This function must be called with the hvcsd->lock held.
 */
static int hvcs_partner_connect(struct hvcs_struct *hvcsd)
{
	int retval;
	unsigned int unit_address = hvcsd->vdev->unit_address;

	/*
	 * If there wasn't any pi when the device was added it doesn't meant
	 * there isn't any now.  This driver isn't notified when a new partner
	 * vty is added to a vty-server so we discover changes on our own.
	 * Please see comments in hvcs_register_connection() for justification
	 * of this bizarre code.
	 */
	retval = hvcs_register_connection(unit_address,
			hvcsd->p_partition_ID,
			hvcsd->p_unit_address);
	if (!retval) {
		hvcsd->connected = 1;
		return 0;
	} else if (retval != -EINVAL)
		return retval;

	/*
	 * As per the spec re-get the pi and try again if -EINVAL after the
	 * first connection attempt.
	 */
	if (hvcs_get_pi(hvcsd))
		return -ENOMEM;

	if (!hvcs_has_pi(hvcsd))
		return -ENODEV;

	retval = hvcs_register_connection(unit_address,
			hvcsd->p_partition_ID,
			hvcsd->p_unit_address);
	if (retval != -EINVAL) {
		hvcsd->connected = 1;
		return retval;
	}

	/*
	 * EBUSY is the most likely scenario though the vty could have been
	 * removed or there really could be an hcall error due to the parameter
	 * data but thanks to ambiguous firmware return codes we can't really
	 * tell.
	 */
	printk(KERN_INFO "HVCS: vty-server or partner"
			" vty is busy.  Try again later.\n");
	return -EBUSY;
}

/* This function must be called with the hvcsd->lock held */
static void hvcs_partner_free(struct hvcs_struct *hvcsd)
{
	int retval;
	do {
		retval = hvcs_free_connection(hvcsd->vdev->unit_address);
	} while (retval == -EBUSY);
	hvcsd->connected = 0;
}

/* This helper function must be called WITHOUT the hvcsd->lock held */
static int hvcs_enable_device(struct hvcs_struct *hvcsd, uint32_t unit_address,
		unsigned int irq, struct vio_dev *vdev)
{
	unsigned long flags;
	int rc;

	/*
	 * It is possible that the vty-server was removed between the time that
	 * the conn was registered and now.
	 */
	if (!(rc = request_irq(irq, &hvcs_handle_interrupt,
				0, "ibmhvcs", hvcsd))) {
		/*
		 * It is possible the vty-server was removed after the irq was
		 * requested but before we have time to enable interrupts.
		 */
		if (vio_enable_interrupts(vdev) == H_SUCCESS)
			return 0;
		else {
			printk(KERN_ERR "HVCS: int enable failed for"
					" vty-server@%X.\n", unit_address);
			free_irq(irq, hvcsd);
		}
	} else
		printk(KERN_ERR "HVCS: irq req failed for"
				" vty-server@%X.\n", unit_address);

	spin_lock_irqsave(&hvcsd->lock, flags);
	hvcs_partner_free(hvcsd);
	spin_unlock_irqrestore(&hvcsd->lock, flags);

	return rc;

}

/*
 * This always increments the kref ref count if the call is successful.
 * Please remember to dec when you are done with the instance.
 *
 * NOTICE: Do NOT hold either the hvcs_struct.lock or hvcs_structs_lock when
 * calling this function or you will get deadlock.
 */
static struct hvcs_struct *hvcs_get_by_index(int index)
{
	struct hvcs_struct *hvcsd;
	unsigned long flags;

	spin_lock(&hvcs_structs_lock);
	list_for_each_entry(hvcsd, &hvcs_structs, next) {
		spin_lock_irqsave(&hvcsd->lock, flags);
		if (hvcsd->index == index) {
			kref_get(&hvcsd->kref);
			spin_unlock_irqrestore(&hvcsd->lock, flags);
			spin_unlock(&hvcs_structs_lock);
			return hvcsd;
		}
		spin_unlock_irqrestore(&hvcsd->lock, flags);
	}
	spin_unlock(&hvcs_structs_lock);

	return NULL;
}

/*
 * This is invoked via the tty_open interface when a user app connects to the
 * /dev node.
 */
static int hvcs_open(struct tty_struct *tty, struct file *filp)
{
	struct hvcs_struct *hvcsd;
	int rc, retval = 0;
	unsigned long flags;
	unsigned int irq;
	struct vio_dev *vdev;
	unsigned long unit_address;

	if (tty->driver_data)
		goto fast_open;

	/*
	 * Is there a vty-server that shares the same index?
	 * This function increments the kref index.
	 */
	if (!(hvcsd = hvcs_get_by_index(tty->index))) {
		printk(KERN_WARNING "HVCS: open failed, no device associated"
				" with tty->index %d.\n", tty->index);
		return -ENODEV;
	}

	spin_lock_irqsave(&hvcsd->lock, flags);

	if (hvcsd->connected == 0)
		if ((retval = hvcs_partner_connect(hvcsd)))
			goto error_release;

	hvcsd->open_count = 1;
	hvcsd->tty = tty;
	tty->driver_data = hvcsd;

	memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);

	/*
	 * Save these in the spinlock for the enable operations that need them
	 * outside of the spinlock.
	 */
	irq = hvcsd->vdev->irq;
	vdev = hvcsd->vdev;
	unit_address = hvcsd->vdev->unit_address;

	hvcsd->todo_mask |= HVCS_SCHED_READ;
	spin_unlock_irqrestore(&hvcsd->lock, flags);

	/*
	 * This must be done outside of the spinlock because it requests irqs
	 * and will grab the spinlock and free the connection if it fails.
	 */
	if (((rc = hvcs_enable_device(hvcsd, unit_address, irq, vdev)))) {
		kref_put(&hvcsd->kref, destroy_hvcs_struct);
		printk(KERN_WARNING "HVCS: enable device failed.\n");
		return rc;
	}

	goto open_success;

fast_open:
	hvcsd = tty->driver_data;

	spin_lock_irqsave(&hvcsd->lock, flags);
	kref_get(&hvcsd->kref);
	hvcsd->open_count++;
	hvcsd->todo_mask |= HVCS_SCHED_READ;
	spin_unlock_irqrestore(&hvcsd->lock, flags);

open_success:
	hvcs_kick();

	printk(KERN_INFO "HVCS: vty-server@%X connection opened.\n",
		hvcsd->vdev->unit_address );

	return 0;

error_release:
	spin_unlock_irqrestore(&hvcsd->lock, flags);
	kref_put(&hvcsd->kref, destroy_hvcs_struct);

	printk(KERN_WARNING "HVCS: partner connect failed.\n");
	return retval;
}

static void hvcs_close(struct tty_struct *tty, struct file *filp)
{
	struct hvcs_struct *hvcsd;
	unsigned long flags;
	int irq;

	/*
	 * Is someone trying to close the file associated with this device after
	 * we have hung up?  If so tty->driver_data wouldn't be valid.
	 */
	if (tty_hung_up_p(filp))
		return;

	/*
	 * No driver_data means that this close was probably issued after a
	 * failed hvcs_open by the tty layer's release_dev() api and we can just
	 * exit cleanly.
	 */
	if (!tty->driver_data)
		return;

	hvcsd = tty->driver_data;

	spin_lock_irqsave(&hvcsd->lock, flags);
	if (--hvcsd->open_count == 0) {

		vio_disable_interrupts(hvcsd->vdev);

		/*
		 * NULL this early so that the kernel_thread doesn't try to
		 * execute any operations on the TTY even though it is obligated
		 * to deliver any pending I/O to the hypervisor.
		 */
		hvcsd->tty = NULL;

		irq = hvcsd->vdev->irq;
		spin_unlock_irqrestore(&hvcsd->lock, flags);

		tty_wait_until_sent_from_close(tty, HVCS_CLOSE_WAIT);

		/*
		 * This line is important because it tells hvcs_open that this
		 * device needs to be re-configured the next time hvcs_open is
		 * called.
		 */
		tty->driver_data = NULL;

		free_irq(irq, hvcsd);
		kref_put(&hvcsd->kref, destroy_hvcs_struct);
		return;
	} else if (hvcsd->open_count < 0) {
		printk(KERN_ERR "HVCS: vty-server@%X open_count: %d"
				" is missmanaged.\n",
		hvcsd->vdev->unit_address, hvcsd->open_count);
	}

	spin_unlock_irqrestore(&hvcsd->lock, flags);
	kref_put(&hvcsd->kref, destroy_hvcs_struct);
}

static void hvcs_hangup(struct tty_struct * tty)
{
	struct hvcs_struct *hvcsd = tty->driver_data;
	unsigned long flags;
	int temp_open_count;
	int irq;

	spin_lock_irqsave(&hvcsd->lock, flags);
	/* Preserve this so that we know how many kref refs to put */
	temp_open_count = hvcsd->open_count;

	/*
	 * Don't kref put inside the spinlock because the destruction
	 * callback may use the spinlock and it may get called before the
	 * spinlock has been released.
	 */
	vio_disable_interrupts(hvcsd->vdev);

	hvcsd->todo_mask = 0;

	/* I don't think the tty needs the hvcs_struct pointer after a hangup */
	hvcsd->tty->driver_data = NULL;
	hvcsd->tty = NULL;

	hvcsd->open_count = 0;

	/* This will drop any buffered data on the floor which is OK in a hangup
	 * scenario. */
	memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);
	hvcsd->chars_in_buffer = 0;

	irq = hvcsd->vdev->irq;

	spin_unlock_irqrestore(&hvcsd->lock, flags);

	free_irq(irq, hvcsd);

	/*
	 * We need to kref_put() for every open_count we have since the
	 * tty_hangup() function doesn't invoke a close per open connection on a
	 * non-console device.
	 */
	while(temp_open_count) {
		--temp_open_count;
		/*
		 * The final put will trigger destruction of the hvcs_struct.
		 * NOTE:  If this hangup was signaled from user space then the
		 * final put will never happen.
		 */
		kref_put(&hvcsd->kref, destroy_hvcs_struct);
	}
}

/*
 * NOTE: This is almost always from_user since user level apps interact with the
 * /dev nodes. I'm trusting that if hvcs_write gets called and interrupted by
 * hvcs_remove (which removes the target device and executes tty_hangup()) that
 * tty_hangup will allow hvcs_write time to complete execution before it
 * terminates our device.
 */
static int hvcs_write(struct tty_struct *tty,
		const unsigned char *buf, int count)
{
	struct hvcs_struct *hvcsd = tty->driver_data;
	unsigned int unit_address;
	const unsigned char *charbuf;
	unsigned long flags;
	int total_sent = 0;
	int tosend = 0;
	int result = 0;

	/*
	 * If they don't check the return code off of their open they may
	 * attempt this even if there is no connected device.
	 */
	if (!hvcsd)
		return -ENODEV;

	/* Reasonable size to prevent user level flooding */
	if (count > HVCS_MAX_FROM_USER) {
		printk(KERN_WARNING "HVCS write: count being truncated to"
				" HVCS_MAX_FROM_USER.\n");
		count = HVCS_MAX_FROM_USER;
	}

	charbuf = buf;

	spin_lock_irqsave(&hvcsd->lock, flags);

	/*
	 * Somehow an open succeeded but the device was removed or the
	 * connection terminated between the vty-server and partner vty during
	 * the middle of a write operation?  This is a crummy place to do this
	 * but we want to keep it all in the spinlock.
	 */
	if (hvcsd->open_count <= 0) {
		spin_unlock_irqrestore(&hvcsd->lock, flags);
		return -ENODEV;
	}

	unit_address = hvcsd->vdev->unit_address;

	while (count > 0) {
		tosend = min(count, (HVCS_BUFF_LEN - hvcsd->chars_in_buffer));
		/*
		 * No more space, this probably means that the last call to
		 * hvcs_write() didn't succeed and the buffer was filled up.
		 */
		if (!tosend)
			break;

		memcpy(&hvcsd->buffer[hvcsd->chars_in_buffer],
				&charbuf[total_sent],
				tosend);

		hvcsd->chars_in_buffer += tosend;

		result = 0;

		/*
		 * If this is true then we don't want to try writing to the
		 * hypervisor because that is the kernel_threads job now.  We'll
		 * just add to the buffer.
		 */
		if (!(hvcsd->todo_mask & HVCS_TRY_WRITE))
			/* won't send partial writes */
			result = hvc_put_chars(unit_address,
					&hvcsd->buffer[0],
					hvcsd->chars_in_buffer);

		/*
		 * Since we know we have enough room in hvcsd->buffer for
		 * tosend we record that it was sent regardless of whether the
		 * hypervisor actually took it because we have it buffered.
		 */
		total_sent+=tosend;
		count-=tosend;
		if (result == 0) {
			hvcsd->todo_mask |= HVCS_TRY_WRITE;
			hvcs_kick();
			break;
		}

		hvcsd->chars_in_buffer = 0;
		/*
		 * Test after the chars_in_buffer reset otherwise this could
		 * deadlock our writes if hvc_put_chars fails.
		 */
		if (result < 0)
			break;
	}

	spin_unlock_irqrestore(&hvcsd->lock, flags);

	if (result == -1)
		return -EIO;
	else
		return total_sent;
}

/*
 * This is really asking how much can we guarantee that we can send or that we
 * absolutely WILL BUFFER if we can't send it.  This driver MUST honor the
 * return value, hence the reason for hvcs_struct buffering.
 */
static int hvcs_write_room(struct tty_struct *tty)
{
	struct hvcs_struct *hvcsd = tty->driver_data;

	if (!hvcsd || hvcsd->open_count <= 0)
		return 0;

	return HVCS_BUFF_LEN - hvcsd->chars_in_buffer;
}

static int hvcs_chars_in_buffer(struct tty_struct *tty)
{
	struct hvcs_struct *hvcsd = tty->driver_data;

	return hvcsd->chars_in_buffer;
}

static const struct tty_operations hvcs_ops = {
	.open = hvcs_open,
	.close = hvcs_close,
	.hangup = hvcs_hangup,
	.write = hvcs_write,
	.write_room = hvcs_write_room,
	.chars_in_buffer = hvcs_chars_in_buffer,
	.unthrottle = hvcs_unthrottle,
	.throttle = hvcs_throttle,
};

static int hvcs_alloc_index_list(int n)
{
	int i;

	hvcs_index_list = kmalloc(n * sizeof(hvcs_index_count),GFP_KERNEL);
	if (!hvcs_index_list)
		return -ENOMEM;
	hvcs_index_count = n;
	for (i = 0; i < hvcs_index_count; i++)
		hvcs_index_list[i] = -1;
	return 0;
}

static void hvcs_free_index_list(void)
{
	/* Paranoia check to be thorough. */
	kfree(hvcs_index_list);
	hvcs_index_list = NULL;
	hvcs_index_count = 0;
}

static int __devinit hvcs_initialize(void)
{
	int rc, num_ttys_to_alloc;

	mutex_lock(&hvcs_init_mutex);
	if (hvcs_task) {
		mutex_unlock(&hvcs_init_mutex);
		return 0;
	}

	/* Has the user specified an overload with an insmod param? */
	if (hvcs_parm_num_devs <= 0 ||
		(hvcs_parm_num_devs > HVCS_MAX_SERVER_ADAPTERS)) {
		num_ttys_to_alloc = HVCS_DEFAULT_SERVER_ADAPTERS;
	} else
		num_ttys_to_alloc = hvcs_parm_num_devs;

	hvcs_tty_driver = alloc_tty_driver(num_ttys_to_alloc);
	if (!hvcs_tty_driver)
		return -ENOMEM;

	if (hvcs_alloc_index_list(num_ttys_to_alloc)) {
		rc = -ENOMEM;
		goto index_fail;
	}

	hvcs_tty_driver->driver_name = hvcs_driver_name;
	hvcs_tty_driver->name = hvcs_device_node;

	/*
	 * We'll let the system assign us a major number, indicated by leaving
	 * it blank.
	 */

	hvcs_tty_driver->minor_start = HVCS_MINOR_START;
	hvcs_tty_driver->type = TTY_DRIVER_TYPE_SYSTEM;

	/*
	 * We role our own so that we DONT ECHO.  We can't echo because the
	 * device we are connecting to already echoes by default and this would
	 * throw us into a horrible recursive echo-echo-echo loop.
	 */
	hvcs_tty_driver->init_termios = hvcs_tty_termios;
	hvcs_tty_driver->flags = TTY_DRIVER_REAL_RAW;

	tty_set_operations(hvcs_tty_driver, &hvcs_ops);

	/*
	 * The following call will result in sysfs entries that denote the
	 * dynamically assigned major and minor numbers for our devices.
	 */
	if (tty_register_driver(hvcs_tty_driver)) {
		printk(KERN_ERR "HVCS: registration as a tty driver failed.\n");
		rc = -EIO;
		goto register_fail;
	}

	hvcs_pi_buff = (unsigned long *) __get_free_page(GFP_KERNEL);
	if (!hvcs_pi_buff) {
		rc = -ENOMEM;
		goto buff_alloc_fail;
	}

	hvcs_task = kthread_run(khvcsd, NULL, "khvcsd");
	if (IS_ERR(hvcs_task)) {
		printk(KERN_ERR "HVCS: khvcsd creation failed.\n");
		rc = -EIO;
		goto kthread_fail;
	}
	mutex_unlock(&hvcs_init_mutex);
	return 0;

kthread_fail:
	free_page((unsigned long)hvcs_pi_buff);
buff_alloc_fail:
	tty_unregister_driver(hvcs_tty_driver);
register_fail:
	hvcs_free_index_list();
index_fail:
	put_tty_driver(hvcs_tty_driver);
	hvcs_tty_driver = NULL;
	mutex_unlock(&hvcs_init_mutex);
	return rc;
}

static int __init hvcs_module_init(void)
{
	int rc = vio_register_driver(&hvcs_vio_driver);
	if (rc) {
		printk(KERN_ERR "HVCS: can't register vio driver\n");
		return rc;
	}

	pr_info("HVCS: Driver registered.\n");

	/* This needs to be done AFTER the vio_register_driver() call or else
	 * the kobjects won't be initialized properly.
	 */
	rc = driver_create_file(&(hvcs_vio_driver.driver), &driver_attr_rescan);
	if (rc)
		pr_warning(KERN_ERR "HVCS: Failed to create rescan file (err %d)\n", rc);

	return 0;
}

static void __exit hvcs_module_exit(void)
{
	/*
	 * This driver receives hvcs_remove callbacks for each device upon
	 * module removal.
	 */
	vio_unregister_driver(&hvcs_vio_driver);
	if (!hvcs_task)
		return;

	/*
	 * This synchronous operation  will wake the khvcsd kthread if it is
	 * asleep and will return when khvcsd has terminated.
	 */
	kthread_stop(hvcs_task);

	spin_lock(&hvcs_pi_lock);
	free_page((unsigned long)hvcs_pi_buff);
	hvcs_pi_buff = NULL;
	spin_unlock(&hvcs_pi_lock);

	driver_remove_file(&hvcs_vio_driver.driver, &driver_attr_rescan);

	tty_unregister_driver(hvcs_tty_driver);

	hvcs_free_index_list();

	put_tty_driver(hvcs_tty_driver);

	printk(KERN_INFO "HVCS: driver module removed.\n");
}

module_init(hvcs_module_init);
module_exit(hvcs_module_exit);