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
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
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
/*
 * udlfb.c -- Framebuffer driver for DisplayLink USB controller
 *
 * Copyright (C) 2009 Roberto De Ioris <roberto@unbit.it>
 * Copyright (C) 2009 Jaya Kumar <jayakumar.lkml@gmail.com>
 * Copyright (C) 2009 Bernie Thompson <bernie@plugable.com>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License v2. See the file COPYING in the main directory of this archive for
 * more details.
 *
 * Layout is based on skeletonfb by James Simmons and Geert Uytterhoeven,
 * usb-skeleton by GregKH.
 *
 * Device-specific portions based on information from Displaylink, with work
 * from Florian Echtler, Henrik Bjerregaard Pedersen, and others.
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/usb.h>
#include <linux/uaccess.h>
#include <linux/mm.h>
#include <linux/fb.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/prefetch.h>
#include <linux/delay.h>
#include <video/udlfb.h>
#include "edid.h"

static struct fb_fix_screeninfo dlfb_fix = {
	.id =           "udlfb",
	.type =         FB_TYPE_PACKED_PIXELS,
	.visual =       FB_VISUAL_TRUECOLOR,
	.xpanstep =     0,
	.ypanstep =     0,
	.ywrapstep =    0,
	.accel =        FB_ACCEL_NONE,
};

static const u32 udlfb_info_flags = FBINFO_DEFAULT | FBINFO_READS_FAST |
		FBINFO_VIRTFB |
		FBINFO_HWACCEL_IMAGEBLIT | FBINFO_HWACCEL_FILLRECT |
		FBINFO_HWACCEL_COPYAREA | FBINFO_MISC_ALWAYS_SETPAR;

/*
 * There are many DisplayLink-based graphics products, all with unique PIDs.
 * So we match on DisplayLink's VID + Vendor-Defined Interface Class (0xff)
 * We also require a match on SubClass (0x00) and Protocol (0x00),
 * which is compatible with all known USB 2.0 era graphics chips and firmware,
 * but allows DisplayLink to increment those for any future incompatible chips
 */
static struct usb_device_id id_table[] = {
	{.idVendor = 0x17e9,
	 .bInterfaceClass = 0xff,
	 .bInterfaceSubClass = 0x00,
	 .bInterfaceProtocol = 0x00,
	 .match_flags = USB_DEVICE_ID_MATCH_VENDOR |
		USB_DEVICE_ID_MATCH_INT_CLASS |
		USB_DEVICE_ID_MATCH_INT_SUBCLASS |
		USB_DEVICE_ID_MATCH_INT_PROTOCOL,
	},
	{},
};
MODULE_DEVICE_TABLE(usb, id_table);

/* module options */
static bool console = 1; /* Allow fbcon to open framebuffer */
static bool fb_defio = 1;  /* Detect mmap writes using page faults */
static bool shadow = 1; /* Optionally disable shadow framebuffer */
static int pixel_limit; /* Optionally force a pixel resolution limit */

/* dlfb keeps a list of urbs for efficient bulk transfers */
static void dlfb_urb_completion(struct urb *urb);
static struct urb *dlfb_get_urb(struct dlfb_data *dev);
static int dlfb_submit_urb(struct dlfb_data *dev, struct urb * urb, size_t len);
static int dlfb_alloc_urb_list(struct dlfb_data *dev, int count, size_t size);
static void dlfb_free_urb_list(struct dlfb_data *dev);

/*
 * All DisplayLink bulk operations start with 0xAF, followed by specific code
 * All operations are written to buffers which then later get sent to device
 */
static char *dlfb_set_register(char *buf, u8 reg, u8 val)
{
	*buf++ = 0xAF;
	*buf++ = 0x20;
	*buf++ = reg;
	*buf++ = val;
	return buf;
}

static char *dlfb_vidreg_lock(char *buf)
{
	return dlfb_set_register(buf, 0xFF, 0x00);
}

static char *dlfb_vidreg_unlock(char *buf)
{
	return dlfb_set_register(buf, 0xFF, 0xFF);
}

/*
 * Map FB_BLANK_* to DisplayLink register
 * DLReg FB_BLANK_*
 * ----- -----------------------------
 *  0x00 FB_BLANK_UNBLANK (0)
 *  0x01 FB_BLANK (1)
 *  0x03 FB_BLANK_VSYNC_SUSPEND (2)
 *  0x05 FB_BLANK_HSYNC_SUSPEND (3)
 *  0x07 FB_BLANK_POWERDOWN (4) Note: requires modeset to come back
 */
static char *dlfb_blanking(char *buf, int fb_blank)
{
	u8 reg;

	switch (fb_blank) {
	case FB_BLANK_POWERDOWN:
		reg = 0x07;
		break;
	case FB_BLANK_HSYNC_SUSPEND:
		reg = 0x05;
		break;
	case FB_BLANK_VSYNC_SUSPEND:
		reg = 0x03;
		break;
	case FB_BLANK_NORMAL:
		reg = 0x01;
		break;
	default:
		reg = 0x00;
	}

	buf = dlfb_set_register(buf, 0x1F, reg);

	return buf;
}

static char *dlfb_set_color_depth(char *buf, u8 selection)
{
	return dlfb_set_register(buf, 0x00, selection);
}

static char *dlfb_set_base16bpp(char *wrptr, u32 base)
{
	/* the base pointer is 16 bits wide, 0x20 is hi byte. */
	wrptr = dlfb_set_register(wrptr, 0x20, base >> 16);
	wrptr = dlfb_set_register(wrptr, 0x21, base >> 8);
	return dlfb_set_register(wrptr, 0x22, base);
}

/*
 * DisplayLink HW has separate 16bpp and 8bpp framebuffers.
 * In 24bpp modes, the low 323 RGB bits go in the 8bpp framebuffer
 */
static char *dlfb_set_base8bpp(char *wrptr, u32 base)
{
	wrptr = dlfb_set_register(wrptr, 0x26, base >> 16);
	wrptr = dlfb_set_register(wrptr, 0x27, base >> 8);
	return dlfb_set_register(wrptr, 0x28, base);
}

static char *dlfb_set_register_16(char *wrptr, u8 reg, u16 value)
{
	wrptr = dlfb_set_register(wrptr, reg, value >> 8);
	return dlfb_set_register(wrptr, reg+1, value);
}

/*
 * This is kind of weird because the controller takes some
 * register values in a different byte order than other registers.
 */
static char *dlfb_set_register_16be(char *wrptr, u8 reg, u16 value)
{
	wrptr = dlfb_set_register(wrptr, reg, value);
	return dlfb_set_register(wrptr, reg+1, value >> 8);
}

/*
 * LFSR is linear feedback shift register. The reason we have this is
 * because the display controller needs to minimize the clock depth of
 * various counters used in the display path. So this code reverses the
 * provided value into the lfsr16 value by counting backwards to get
 * the value that needs to be set in the hardware comparator to get the
 * same actual count. This makes sense once you read above a couple of
 * times and think about it from a hardware perspective.
 */
static u16 dlfb_lfsr16(u16 actual_count)
{
	u32 lv = 0xFFFF; /* This is the lfsr value that the hw starts with */

	while (actual_count--) {
		lv =	 ((lv << 1) |
			(((lv >> 15) ^ (lv >> 4) ^ (lv >> 2) ^ (lv >> 1)) & 1))
			& 0xFFFF;
	}

	return (u16) lv;
}

/*
 * This does LFSR conversion on the value that is to be written.
 * See LFSR explanation above for more detail.
 */
static char *dlfb_set_register_lfsr16(char *wrptr, u8 reg, u16 value)
{
	return dlfb_set_register_16(wrptr, reg, dlfb_lfsr16(value));
}

/*
 * This takes a standard fbdev screeninfo struct and all of its monitor mode
 * details and converts them into the DisplayLink equivalent register commands.
 */
static char *dlfb_set_vid_cmds(char *wrptr, struct fb_var_screeninfo *var)
{
	u16 xds, yds;
	u16 xde, yde;
	u16 yec;

	/* x display start */
	xds = var->left_margin + var->hsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x01, xds);
	/* x display end */
	xde = xds + var->xres;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x03, xde);

	/* y display start */
	yds = var->upper_margin + var->vsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x05, yds);
	/* y display end */
	yde = yds + var->yres;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x07, yde);

	/* x end count is active + blanking - 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x09,
			xde + var->right_margin - 1);

	/* libdlo hardcodes hsync start to 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x0B, 1);

	/* hsync end is width of sync pulse + 1 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x0D, var->hsync_len + 1);

	/* hpixels is active pixels */
	wrptr = dlfb_set_register_16(wrptr, 0x0F, var->xres);

	/* yendcount is vertical active + vertical blanking */
	yec = var->yres + var->upper_margin + var->lower_margin +
			var->vsync_len;
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x11, yec);

	/* libdlo hardcodes vsync start to 0 */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x13, 0);

	/* vsync end is width of vsync pulse */
	wrptr = dlfb_set_register_lfsr16(wrptr, 0x15, var->vsync_len);

	/* vpixels is active pixels */
	wrptr = dlfb_set_register_16(wrptr, 0x17, var->yres);

	/* convert picoseconds to 5kHz multiple for pclk5k = x * 1E12/5k */
	wrptr = dlfb_set_register_16be(wrptr, 0x1B,
			200*1000*1000/var->pixclock);

	return wrptr;
}

/*
 * This takes a standard fbdev screeninfo struct that was fetched or prepared
 * and then generates the appropriate command sequence that then drives the
 * display controller.
 */
static int dlfb_set_video_mode(struct dlfb_data *dev,
				struct fb_var_screeninfo *var)
{
	char *buf;
	char *wrptr;
	int retval;
	int writesize;
	struct urb *urb;

	if (!atomic_read(&dev->usb_active))
		return -EPERM;

	urb = dlfb_get_urb(dev);
	if (!urb)
		return -ENOMEM;

	buf = (char *) urb->transfer_buffer;

	/*
	* This first section has to do with setting the base address on the
	* controller * associated with the display. There are 2 base
	* pointers, currently, we only * use the 16 bpp segment.
	*/
	wrptr = dlfb_vidreg_lock(buf);
	wrptr = dlfb_set_color_depth(wrptr, 0x00);
	/* set base for 16bpp segment to 0 */
	wrptr = dlfb_set_base16bpp(wrptr, 0);
	/* set base for 8bpp segment to end of fb */
	wrptr = dlfb_set_base8bpp(wrptr, dev->info->fix.smem_len);

	wrptr = dlfb_set_vid_cmds(wrptr, var);
	wrptr = dlfb_blanking(wrptr, FB_BLANK_UNBLANK);
	wrptr = dlfb_vidreg_unlock(wrptr);

	writesize = wrptr - buf;

	retval = dlfb_submit_urb(dev, urb, writesize);

	dev->blank_mode = FB_BLANK_UNBLANK;

	return retval;
}

static int dlfb_ops_mmap(struct fb_info *info, struct vm_area_struct *vma)
{
	unsigned long start = vma->vm_start;
	unsigned long size = vma->vm_end - vma->vm_start;
	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
	unsigned long page, pos;

	if (vma->vm_pgoff > (~0UL >> PAGE_SHIFT))
		return -EINVAL;
	if (size > info->fix.smem_len)
		return -EINVAL;
	if (offset > info->fix.smem_len - size)
		return -EINVAL;

	pos = (unsigned long)info->fix.smem_start + offset;

	pr_notice("mmap() framebuffer addr:%lu size:%lu\n",
		  pos, size);

	while (size > 0) {
		page = vmalloc_to_pfn((void *)pos);
		if (remap_pfn_range(vma, start, page, PAGE_SIZE, PAGE_SHARED))
			return -EAGAIN;

		start += PAGE_SIZE;
		pos += PAGE_SIZE;
		if (size > PAGE_SIZE)
			size -= PAGE_SIZE;
		else
			size = 0;
	}

	return 0;
}

/*
 * Trims identical data from front and back of line
 * Sets new front buffer address and width
 * And returns byte count of identical pixels
 * Assumes CPU natural alignment (unsigned long)
 * for back and front buffer ptrs and width
 */
static int dlfb_trim_hline(const u8 *bback, const u8 **bfront, int *width_bytes)
{
	int j, k;
	const unsigned long *back = (const unsigned long *) bback;
	const unsigned long *front = (const unsigned long *) *bfront;
	const int width = *width_bytes / sizeof(unsigned long);
	int identical = width;
	int start = width;
	int end = width;

	prefetch((void *) front);
	prefetch((void *) back);

	for (j = 0; j < width; j++) {
		if (back[j] != front[j]) {
			start = j;
			break;
		}
	}

	for (k = width - 1; k > j; k--) {
		if (back[k] != front[k]) {
			end = k+1;
			break;
		}
	}

	identical = start + (width - end);
	*bfront = (u8 *) &front[start];
	*width_bytes = (end - start) * sizeof(unsigned long);

	return identical * sizeof(unsigned long);
}

/*
 * Render a command stream for an encoded horizontal line segment of pixels.
 *
 * A command buffer holds several commands.
 * It always begins with a fresh command header
 * (the protocol doesn't require this, but we enforce it to allow
 * multiple buffers to be potentially encoded and sent in parallel).
 * A single command encodes one contiguous horizontal line of pixels
 *
 * The function relies on the client to do all allocation, so that
 * rendering can be done directly to output buffers (e.g. USB URBs).
 * The function fills the supplied command buffer, providing information
 * on where it left off, so the client may call in again with additional
 * buffers if the line will take several buffers to complete.
 *
 * A single command can transmit a maximum of 256 pixels,
 * regardless of the compression ratio (protocol design limit).
 * To the hardware, 0 for a size byte means 256
 *
 * Rather than 256 pixel commands which are either rl or raw encoded,
 * the rlx command simply assumes alternating raw and rl spans within one cmd.
 * This has a slightly larger header overhead, but produces more even results.
 * It also processes all data (read and write) in a single pass.
 * Performance benchmarks of common cases show it having just slightly better
 * compression than 256 pixel raw or rle commands, with similar CPU consumpion.
 * But for very rl friendly data, will compress not quite as well.
 */
static void dlfb_compress_hline(
	const uint16_t **pixel_start_ptr,
	const uint16_t *const pixel_end,
	uint32_t *device_address_ptr,
	uint8_t **command_buffer_ptr,
	const uint8_t *const cmd_buffer_end)
{
	const uint16_t *pixel = *pixel_start_ptr;
	uint32_t dev_addr  = *device_address_ptr;
	uint8_t *cmd = *command_buffer_ptr;
	const int bpp = 2;

	while ((pixel_end > pixel) &&
	       (cmd_buffer_end - MIN_RLX_CMD_BYTES > cmd)) {
		uint8_t *raw_pixels_count_byte = NULL;
		uint8_t *cmd_pixels_count_byte = NULL;
		const uint16_t *raw_pixel_start = NULL;
		const uint16_t *cmd_pixel_start, *cmd_pixel_end = NULL;

		prefetchw((void *) cmd); /* pull in one cache line at least */

		*cmd++ = 0xAF;
		*cmd++ = 0x6B;
		*cmd++ = (uint8_t) ((dev_addr >> 16) & 0xFF);
		*cmd++ = (uint8_t) ((dev_addr >> 8) & 0xFF);
		*cmd++ = (uint8_t) ((dev_addr) & 0xFF);

		cmd_pixels_count_byte = cmd++; /*  we'll know this later */
		cmd_pixel_start = pixel;

		raw_pixels_count_byte = cmd++; /*  we'll know this later */
		raw_pixel_start = pixel;

		cmd_pixel_end = pixel + min(MAX_CMD_PIXELS + 1,
			min((int)(pixel_end - pixel),
			    (int)(cmd_buffer_end - cmd) / bpp));

		prefetch_range((void *) pixel, (cmd_pixel_end - pixel) * bpp);

		while (pixel < cmd_pixel_end) {
			const uint16_t * const repeating_pixel = pixel;

			*(uint16_t *)cmd = cpu_to_be16p(pixel);
			cmd += 2;
			pixel++;

			if (unlikely((pixel < cmd_pixel_end) &&
				     (*pixel == *repeating_pixel))) {
				/* go back and fill in raw pixel count */
				*raw_pixels_count_byte = ((repeating_pixel -
						raw_pixel_start) + 1) & 0xFF;

				while ((pixel < cmd_pixel_end)
				       && (*pixel == *repeating_pixel)) {
					pixel++;
				}

				/* immediately after raw data is repeat byte */
				*cmd++ = ((pixel - repeating_pixel) - 1) & 0xFF;

				/* Then start another raw pixel span */
				raw_pixel_start = pixel;
				raw_pixels_count_byte = cmd++;
			}
		}

		if (pixel > raw_pixel_start) {
			/* finalize last RAW span */
			*raw_pixels_count_byte = (pixel-raw_pixel_start) & 0xFF;
		}

		*cmd_pixels_count_byte = (pixel - cmd_pixel_start) & 0xFF;
		dev_addr += (pixel - cmd_pixel_start) * bpp;
	}

	if (cmd_buffer_end <= MIN_RLX_CMD_BYTES + cmd) {
		/* Fill leftover bytes with no-ops */
		if (cmd_buffer_end > cmd)
			memset(cmd, 0xAF, cmd_buffer_end - cmd);
		cmd = (uint8_t *) cmd_buffer_end;
	}

	*command_buffer_ptr = cmd;
	*pixel_start_ptr = pixel;
	*device_address_ptr = dev_addr;

	return;
}

/*
 * There are 3 copies of every pixel: The front buffer that the fbdev
 * client renders to, the actual framebuffer across the USB bus in hardware
 * (that we can only write to, slowly, and can never read), and (optionally)
 * our shadow copy that tracks what's been sent to that hardware buffer.
 */
static int dlfb_render_hline(struct dlfb_data *dev, struct urb **urb_ptr,
			      const char *front, char **urb_buf_ptr,
			      u32 byte_offset, u32 byte_width,
			      int *ident_ptr, int *sent_ptr)
{
	const u8 *line_start, *line_end, *next_pixel;
	u32 dev_addr = dev->base16 + byte_offset;
	struct urb *urb = *urb_ptr;
	u8 *cmd = *urb_buf_ptr;
	u8 *cmd_end = (u8 *) urb->transfer_buffer + urb->transfer_buffer_length;

	line_start = (u8 *) (front + byte_offset);
	next_pixel = line_start;
	line_end = next_pixel + byte_width;

	if (dev->backing_buffer) {
		int offset;
		const u8 *back_start = (u8 *) (dev->backing_buffer
						+ byte_offset);

		*ident_ptr += dlfb_trim_hline(back_start, &next_pixel,
			&byte_width);

		offset = next_pixel - line_start;
		line_end = next_pixel + byte_width;
		dev_addr += offset;
		back_start += offset;
		line_start += offset;

		memcpy((char *)back_start, (char *) line_start,
		       byte_width);
	}

	while (next_pixel < line_end) {

		dlfb_compress_hline((const uint16_t **) &next_pixel,
			     (const uint16_t *) line_end, &dev_addr,
			(u8 **) &cmd, (u8 *) cmd_end);

		if (cmd >= cmd_end) {
			int len = cmd - (u8 *) urb->transfer_buffer;
			if (dlfb_submit_urb(dev, urb, len))
				return 1; /* lost pixels is set */
			*sent_ptr += len;
			urb = dlfb_get_urb(dev);
			if (!urb)
				return 1; /* lost_pixels is set */
			*urb_ptr = urb;
			cmd = urb->transfer_buffer;
			cmd_end = &cmd[urb->transfer_buffer_length];
		}
	}

	*urb_buf_ptr = cmd;

	return 0;
}

static int dlfb_handle_damage(struct dlfb_data *dev, int x, int y,
	       int width, int height, char *data)
{
	int i, ret;
	char *cmd;
	cycles_t start_cycles, end_cycles;
	int bytes_sent = 0;
	int bytes_identical = 0;
	struct urb *urb;
	int aligned_x;

	start_cycles = get_cycles();

	aligned_x = DL_ALIGN_DOWN(x, sizeof(unsigned long));
	width = DL_ALIGN_UP(width + (x-aligned_x), sizeof(unsigned long));
	x = aligned_x;

	if ((width <= 0) ||
	    (x + width > dev->info->var.xres) ||
	    (y + height > dev->info->var.yres))
		return -EINVAL;

	if (!atomic_read(&dev->usb_active))
		return 0;

	urb = dlfb_get_urb(dev);
	if (!urb)
		return 0;
	cmd = urb->transfer_buffer;

	for (i = y; i < y + height ; i++) {
		const int line_offset = dev->info->fix.line_length * i;
		const int byte_offset = line_offset + (x * BPP);

		if (dlfb_render_hline(dev, &urb,
				      (char *) dev->info->fix.smem_start,
				      &cmd, byte_offset, width * BPP,
				      &bytes_identical, &bytes_sent))
			goto error;
	}

	if (cmd > (char *) urb->transfer_buffer) {
		/* Send partial buffer remaining before exiting */
		int len = cmd - (char *) urb->transfer_buffer;
		ret = dlfb_submit_urb(dev, urb, len);
		bytes_sent += len;
	} else
		dlfb_urb_completion(urb);

error:
	atomic_add(bytes_sent, &dev->bytes_sent);
	atomic_add(bytes_identical, &dev->bytes_identical);
	atomic_add(width*height*2, &dev->bytes_rendered);
	end_cycles = get_cycles();
	atomic_add(((unsigned int) ((end_cycles - start_cycles)
		    >> 10)), /* Kcycles */
		   &dev->cpu_kcycles_used);

	return 0;
}

/*
 * Path triggered by usermode clients who write to filesystem
 * e.g. cat filename > /dev/fb1
 * Not used by X Windows or text-mode console. But useful for testing.
 * Slow because of extra copy and we must assume all pixels dirty.
 */
static ssize_t dlfb_ops_write(struct fb_info *info, const char __user *buf,
			  size_t count, loff_t *ppos)
{
	ssize_t result;
	struct dlfb_data *dev = info->par;
	u32 offset = (u32) *ppos;

	result = fb_sys_write(info, buf, count, ppos);

	if (result > 0) {
		int start = max((int)(offset / info->fix.line_length), 0);
		int lines = min((u32)((result / info->fix.line_length) + 1),
				(u32)info->var.yres);

		dlfb_handle_damage(dev, 0, start, info->var.xres,
			lines, info->screen_base);
	}

	return result;
}

/* hardware has native COPY command (see libdlo), but not worth it for fbcon */
static void dlfb_ops_copyarea(struct fb_info *info,
				const struct fb_copyarea *area)
{

	struct dlfb_data *dev = info->par;

	sys_copyarea(info, area);

	dlfb_handle_damage(dev, area->dx, area->dy,
			area->width, area->height, info->screen_base);
}

static void dlfb_ops_imageblit(struct fb_info *info,
				const struct fb_image *image)
{
	struct dlfb_data *dev = info->par;

	sys_imageblit(info, image);

	dlfb_handle_damage(dev, image->dx, image->dy,
			image->width, image->height, info->screen_base);
}

static void dlfb_ops_fillrect(struct fb_info *info,
			  const struct fb_fillrect *rect)
{
	struct dlfb_data *dev = info->par;

	sys_fillrect(info, rect);

	dlfb_handle_damage(dev, rect->dx, rect->dy, rect->width,
			      rect->height, info->screen_base);
}

/*
 * NOTE: fb_defio.c is holding info->fbdefio.mutex
 *   Touching ANY framebuffer memory that triggers a page fault
 *   in fb_defio will cause a deadlock, when it also tries to
 *   grab the same mutex.
 */
static void dlfb_dpy_deferred_io(struct fb_info *info,
				struct list_head *pagelist)
{
	struct page *cur;
	struct fb_deferred_io *fbdefio = info->fbdefio;
	struct dlfb_data *dev = info->par;
	struct urb *urb;
	char *cmd;
	cycles_t start_cycles, end_cycles;
	int bytes_sent = 0;
	int bytes_identical = 0;
	int bytes_rendered = 0;

	if (!fb_defio)
		return;

	if (!atomic_read(&dev->usb_active))
		return;

	start_cycles = get_cycles();

	urb = dlfb_get_urb(dev);
	if (!urb)
		return;

	cmd = urb->transfer_buffer;

	/* walk the written page list and render each to device */
	list_for_each_entry(cur, &fbdefio->pagelist, lru) {

		if (dlfb_render_hline(dev, &urb, (char *) info->fix.smem_start,
				  &cmd, cur->index << PAGE_SHIFT,
				  PAGE_SIZE, &bytes_identical, &bytes_sent))
			goto error;
		bytes_rendered += PAGE_SIZE;
	}

	if (cmd > (char *) urb->transfer_buffer) {
		/* Send partial buffer remaining before exiting */
		int len = cmd - (char *) urb->transfer_buffer;
		dlfb_submit_urb(dev, urb, len);
		bytes_sent += len;
	} else
		dlfb_urb_completion(urb);

error:
	atomic_add(bytes_sent, &dev->bytes_sent);
	atomic_add(bytes_identical, &dev->bytes_identical);
	atomic_add(bytes_rendered, &dev->bytes_rendered);
	end_cycles = get_cycles();
	atomic_add(((unsigned int) ((end_cycles - start_cycles)
		    >> 10)), /* Kcycles */
		   &dev->cpu_kcycles_used);
}

static int dlfb_get_edid(struct dlfb_data *dev, char *edid, int len)
{
	int i;
	int ret;
	char *rbuf;

	rbuf = kmalloc(2, GFP_KERNEL);
	if (!rbuf)
		return 0;

	for (i = 0; i < len; i++) {
		ret = usb_control_msg(dev->udev,
				    usb_rcvctrlpipe(dev->udev, 0), (0x02),
				    (0x80 | (0x02 << 5)), i << 8, 0xA1, rbuf, 2,
				    HZ);
		if (ret < 1) {
			pr_err("Read EDID byte %d failed err %x\n", i, ret);
			i--;
			break;
		}
		edid[i] = rbuf[1];
	}

	kfree(rbuf);

	return i;
}

static int dlfb_ops_ioctl(struct fb_info *info, unsigned int cmd,
				unsigned long arg)
{

	struct dlfb_data *dev = info->par;

	if (!atomic_read(&dev->usb_active))
		return 0;

	/* TODO: Update X server to get this from sysfs instead */
	if (cmd == DLFB_IOCTL_RETURN_EDID) {
		void __user *edid = (void __user *)arg;
		if (copy_to_user(edid, dev->edid, dev->edid_size))
			return -EFAULT;
		return 0;
	}

	/* TODO: Help propose a standard fb.h ioctl to report mmap damage */
	if (cmd == DLFB_IOCTL_REPORT_DAMAGE) {
		struct dloarea area;

		if (copy_from_user(&area, (void __user *)arg,
				  sizeof(struct dloarea)))
			return -EFAULT;

		/*
		 * If we have a damage-aware client, turn fb_defio "off"
		 * To avoid perf imact of unnecessary page fault handling.
		 * Done by resetting the delay for this fb_info to a very
		 * long period. Pages will become writable and stay that way.
		 * Reset to normal value when all clients have closed this fb.
		 */
		if (info->fbdefio)
			info->fbdefio->delay = DL_DEFIO_WRITE_DISABLE;

		if (area.x < 0)
			area.x = 0;

		if (area.x > info->var.xres)
			area.x = info->var.xres;

		if (area.y < 0)
			area.y = 0;

		if (area.y > info->var.yres)
			area.y = info->var.yres;

		dlfb_handle_damage(dev, area.x, area.y, area.w, area.h,
			   info->screen_base);
	}

	return 0;
}

/* taken from vesafb */
static int
dlfb_ops_setcolreg(unsigned regno, unsigned red, unsigned green,
	       unsigned blue, unsigned transp, struct fb_info *info)
{
	int err = 0;

	if (regno >= info->cmap.len)
		return 1;

	if (regno < 16) {
		if (info->var.red.offset == 10) {
			/* 1:5:5:5 */
			((u32 *) (info->pseudo_palette))[regno] =
			    ((red & 0xf800) >> 1) |
			    ((green & 0xf800) >> 6) | ((blue & 0xf800) >> 11);
		} else {
			/* 0:5:6:5 */
			((u32 *) (info->pseudo_palette))[regno] =
			    ((red & 0xf800)) |
			    ((green & 0xfc00) >> 5) | ((blue & 0xf800) >> 11);
		}
	}

	return err;
}

/*
 * It's common for several clients to have framebuffer open simultaneously.
 * e.g. both fbcon and X. Makes things interesting.
 * Assumes caller is holding info->lock (for open and release at least)
 */
static int dlfb_ops_open(struct fb_info *info, int user)
{
	struct dlfb_data *dev = info->par;

	/*
	 * fbcon aggressively connects to first framebuffer it finds,
	 * preventing other clients (X) from working properly. Usually
	 * not what the user wants. Fail by default with option to enable.
	 */
	if ((user == 0) && (!console))
		return -EBUSY;

	/* If the USB device is gone, we don't accept new opens */
	if (dev->virtualized)
		return -ENODEV;

	dev->fb_count++;

	kref_get(&dev->kref);

	if (fb_defio && (info->fbdefio == NULL)) {
		/* enable defio at last moment if not disabled by client */

		struct fb_deferred_io *fbdefio;

		fbdefio = kzalloc(sizeof(struct fb_deferred_io), GFP_KERNEL);

		if (fbdefio) {
			fbdefio->delay = DL_DEFIO_WRITE_DELAY;
			fbdefio->deferred_io = dlfb_dpy_deferred_io;
		}

		info->fbdefio = fbdefio;
		fb_deferred_io_init(info);
	}

	pr_notice("open /dev/fb%d user=%d fb_info=%p count=%d\n",
	    info->node, user, info, dev->fb_count);

	return 0;
}

/*
 * Called when all client interfaces to start transactions have been disabled,
 * and all references to our device instance (dlfb_data) are released.
 * Every transaction must have a reference, so we know are fully spun down
 */
static void dlfb_free(struct kref *kref)
{
	struct dlfb_data *dev = container_of(kref, struct dlfb_data, kref);

	vfree(dev->backing_buffer);

	kfree(dev->edid);

	pr_warn("freeing dlfb_data %p\n", dev);

	kfree(dev);
}

static void dlfb_release_urb_work(struct work_struct *work)
{
	struct urb_node *unode = container_of(work, struct urb_node,
					      release_urb_work.work);

	up(&unode->dev->urbs.limit_sem);
}

static void dlfb_free_framebuffer(struct dlfb_data *dev)
{
	struct fb_info *info = dev->info;

	if (info) {
		int node = info->node;

		unregister_framebuffer(info);

		if (info->cmap.len != 0)
			fb_dealloc_cmap(&info->cmap);
		if (info->monspecs.modedb)
			fb_destroy_modedb(info->monspecs.modedb);
		vfree(info->screen_base);

		fb_destroy_modelist(&info->modelist);

		dev->info = NULL;

		/* Assume info structure is freed after this point */
		framebuffer_release(info);

		pr_warn("fb_info for /dev/fb%d has been freed\n", node);
	}

	/* ref taken in probe() as part of registering framebfufer */
	kref_put(&dev->kref, dlfb_free);
}

static void dlfb_free_framebuffer_work(struct work_struct *work)
{
	struct dlfb_data *dev = container_of(work, struct dlfb_data,
					     free_framebuffer_work.work);
	dlfb_free_framebuffer(dev);
}
/*
 * Assumes caller is holding info->lock mutex (for open and release at least)
 */
static int dlfb_ops_release(struct fb_info *info, int user)
{
	struct dlfb_data *dev = info->par;

	dev->fb_count--;

	/* We can't free fb_info here - fbmem will touch it when we return */
	if (dev->virtualized && (dev->fb_count == 0))
		schedule_delayed_work(&dev->free_framebuffer_work, HZ);

	if ((dev->fb_count == 0) && (info->fbdefio)) {
		fb_deferred_io_cleanup(info);
		kfree(info->fbdefio);
		info->fbdefio = NULL;
		info->fbops->fb_mmap = dlfb_ops_mmap;
	}

	pr_warn("released /dev/fb%d user=%d count=%d\n",
		  info->node, user, dev->fb_count);

	kref_put(&dev->kref, dlfb_free);

	return 0;
}

/*
 * Check whether a video mode is supported by the DisplayLink chip
 * We start from monitor's modes, so don't need to filter that here
 */
static int dlfb_is_valid_mode(struct fb_videomode *mode,
		struct fb_info *info)
{
	struct dlfb_data *dev = info->par;

	if (mode->xres * mode->yres > dev->sku_pixel_limit) {
		pr_warn("%dx%d beyond chip capabilities\n",
		       mode->xres, mode->yres);
		return 0;
	}

	pr_info("%dx%d @ %d Hz valid mode\n", mode->xres, mode->yres,
		mode->refresh);

	return 1;
}

static void dlfb_var_color_format(struct fb_var_screeninfo *var)
{
	const struct fb_bitfield red = { 11, 5, 0 };
	const struct fb_bitfield green = { 5, 6, 0 };
	const struct fb_bitfield blue = { 0, 5, 0 };

	var->bits_per_pixel = 16;
	var->red = red;
	var->green = green;
	var->blue = blue;
}

static int dlfb_ops_check_var(struct fb_var_screeninfo *var,
				struct fb_info *info)
{
	struct fb_videomode mode;

	/* TODO: support dynamically changing framebuffer size */
	if ((var->xres * var->yres * 2) > info->fix.smem_len)
		return -EINVAL;

	/* set device-specific elements of var unrelated to mode */
	dlfb_var_color_format(var);

	fb_var_to_videomode(&mode, var);

	if (!dlfb_is_valid_mode(&mode, info))
		return -EINVAL;

	return 0;
}

static int dlfb_ops_set_par(struct fb_info *info)
{
	struct dlfb_data *dev = info->par;
	int result;
	u16 *pix_framebuffer;
	int i;

	pr_notice("set_par mode %dx%d\n", info->var.xres, info->var.yres);

	result = dlfb_set_video_mode(dev, &info->var);

	if ((result == 0) && (dev->fb_count == 0)) {

		/* paint greenscreen */

		pix_framebuffer = (u16 *) info->screen_base;
		for (i = 0; i < info->fix.smem_len / 2; i++)
			pix_framebuffer[i] = 0x37e6;

		dlfb_handle_damage(dev, 0, 0, info->var.xres, info->var.yres,
				   info->screen_base);
	}

	return result;
}

/* To fonzi the jukebox (e.g. make blanking changes take effect) */
static char *dlfb_dummy_render(char *buf)
{
	*buf++ = 0xAF;
	*buf++ = 0x6A; /* copy */
	*buf++ = 0x00; /* from address*/
	*buf++ = 0x00;
	*buf++ = 0x00;
	*buf++ = 0x01; /* one pixel */
	*buf++ = 0x00; /* to address */
	*buf++ = 0x00;
	*buf++ = 0x00;
	return buf;
}

/*
 * In order to come back from full DPMS off, we need to set the mode again
 */
static int dlfb_ops_blank(int blank_mode, struct fb_info *info)
{
	struct dlfb_data *dev = info->par;
	char *bufptr;
	struct urb *urb;

	pr_debug("/dev/fb%d FB_BLANK mode %d --> %d\n",
		 info->node, dev->blank_mode, blank_mode);

	if ((dev->blank_mode == FB_BLANK_POWERDOWN) &&
	    (blank_mode != FB_BLANK_POWERDOWN)) {

		/* returning from powerdown requires a fresh modeset */
		dlfb_set_video_mode(dev, &info->var);
	}

	urb = dlfb_get_urb(dev);
	if (!urb)
		return 0;

	bufptr = (char *) urb->transfer_buffer;
	bufptr = dlfb_vidreg_lock(bufptr);
	bufptr = dlfb_blanking(bufptr, blank_mode);
	bufptr = dlfb_vidreg_unlock(bufptr);

	/* seems like a render op is needed to have blank change take effect */
	bufptr = dlfb_dummy_render(bufptr);

	dlfb_submit_urb(dev, urb, bufptr -
			(char *) urb->transfer_buffer);

	dev->blank_mode = blank_mode;

	return 0;
}

static struct fb_ops dlfb_ops = {
	.owner = THIS_MODULE,
	.fb_read = fb_sys_read,
	.fb_write = dlfb_ops_write,
	.fb_setcolreg = dlfb_ops_setcolreg,
	.fb_fillrect = dlfb_ops_fillrect,
	.fb_copyarea = dlfb_ops_copyarea,
	.fb_imageblit = dlfb_ops_imageblit,
	.fb_mmap = dlfb_ops_mmap,
	.fb_ioctl = dlfb_ops_ioctl,
	.fb_open = dlfb_ops_open,
	.fb_release = dlfb_ops_release,
	.fb_blank = dlfb_ops_blank,
	.fb_check_var = dlfb_ops_check_var,
	.fb_set_par = dlfb_ops_set_par,
};


/*
 * Assumes &info->lock held by caller
 * Assumes no active clients have framebuffer open
 */
static int dlfb_realloc_framebuffer(struct dlfb_data *dev, struct fb_info *info)
{
	int retval = -ENOMEM;
	int old_len = info->fix.smem_len;
	int new_len;
	unsigned char *old_fb = info->screen_base;
	unsigned char *new_fb;
	unsigned char *new_back = NULL;

	pr_warn("Reallocating framebuffer. Addresses will change!\n");

	new_len = info->fix.line_length * info->var.yres;

	if (PAGE_ALIGN(new_len) > old_len) {
		/*
		 * Alloc system memory for virtual framebuffer
		 */
		new_fb = vmalloc(new_len);
		if (!new_fb) {
			pr_err("Virtual framebuffer alloc failed\n");
			goto error;
		}

		if (info->screen_base) {
			memcpy(new_fb, old_fb, old_len);
			vfree(info->screen_base);
		}

		info->screen_base = new_fb;
		info->fix.smem_len = PAGE_ALIGN(new_len);
		info->fix.smem_start = (unsigned long) new_fb;
		info->flags = udlfb_info_flags;

		/*
		 * Second framebuffer copy to mirror the framebuffer state
		 * on the physical USB device. We can function without this.
		 * But with imperfect damage info we may send pixels over USB
		 * that were, in fact, unchanged - wasting limited USB bandwidth
		 */
		if (shadow)
			new_back = vzalloc(new_len);
		if (!new_back)
			pr_info("No shadow/backing buffer allocated\n");
		else {
			vfree(dev->backing_buffer);
			dev->backing_buffer = new_back;
		}
	}

	retval = 0;

error:
	return retval;
}

/*
 * 1) Get EDID from hw, or use sw default
 * 2) Parse into various fb_info structs
 * 3) Allocate virtual framebuffer memory to back highest res mode
 *
 * Parses EDID into three places used by various parts of fbdev:
 * fb_var_screeninfo contains the timing of the monitor's preferred mode
 * fb_info.monspecs is full parsed EDID info, including monspecs.modedb
 * fb_info.modelist is a linked list of all monitor & VESA modes which work
 *
 * If EDID is not readable/valid, then modelist is all VESA modes,
 * monspecs is NULL, and fb_var_screeninfo is set to safe VESA mode
 * Returns 0 if successful
 */
static int dlfb_setup_modes(struct dlfb_data *dev,
			   struct fb_info *info,
			   char *default_edid, size_t default_edid_size)
{
	int i;
	const struct fb_videomode *default_vmode = NULL;
	int result = 0;
	char *edid;
	int tries = 3;

	if (info->dev) /* only use mutex if info has been registered */
		mutex_lock(&info->lock);

	edid = kmalloc(EDID_LENGTH, GFP_KERNEL);
	if (!edid) {
		result = -ENOMEM;
		goto error;
	}

	fb_destroy_modelist(&info->modelist);
	memset(&info->monspecs, 0, sizeof(info->monspecs));

	/*
	 * Try to (re)read EDID from hardware first
	 * EDID data may return, but not parse as valid
	 * Try again a few times, in case of e.g. analog cable noise
	 */
	while (tries--) {

		i = dlfb_get_edid(dev, edid, EDID_LENGTH);

		if (i >= EDID_LENGTH)
			fb_edid_to_monspecs(edid, &info->monspecs);

		if (info->monspecs.modedb_len > 0) {
			dev->edid = edid;
			dev->edid_size = i;
			break;
		}
	}

	/* If that fails, use a previously returned EDID if available */
	if (info->monspecs.modedb_len == 0) {

		pr_err("Unable to get valid EDID from device/display\n");

		if (dev->edid) {
			fb_edid_to_monspecs(dev->edid, &info->monspecs);
			if (info->monspecs.modedb_len > 0)
				pr_err("Using previously queried EDID\n");
		}
	}

	/* If that fails, use the default EDID we were handed */
	if (info->monspecs.modedb_len == 0) {
		if (default_edid_size >= EDID_LENGTH) {
			fb_edid_to_monspecs(default_edid, &info->monspecs);
			if (info->monspecs.modedb_len > 0) {
				memcpy(edid, default_edid, default_edid_size);
				dev->edid = edid;
				dev->edid_size = default_edid_size;
				pr_err("Using default/backup EDID\n");
			}
		}
	}

	/* If we've got modes, let's pick a best default mode */
	if (info->monspecs.modedb_len > 0) {

		for (i = 0; i < info->monspecs.modedb_len; i++) {
			if (dlfb_is_valid_mode(&info->monspecs.modedb[i], info))
				fb_add_videomode(&info->monspecs.modedb[i],
					&info->modelist);
			else {
				if (i == 0)
					/* if we've removed top/best mode */
					info->monspecs.misc
						&= ~FB_MISC_1ST_DETAIL;
			}
		}

		default_vmode = fb_find_best_display(&info->monspecs,
						     &info->modelist);
	}

	/* If everything else has failed, fall back to safe default mode */
	if (default_vmode == NULL) {

		struct fb_videomode fb_vmode = {0};

		/*
		 * Add the standard VESA modes to our modelist
		 * Since we don't have EDID, there may be modes that
		 * overspec monitor and/or are incorrect aspect ratio, etc.
		 * But at least the user has a chance to choose
		 */
		for (i = 0; i < VESA_MODEDB_SIZE; i++) {
			if (dlfb_is_valid_mode((struct fb_videomode *)
						&vesa_modes[i], info))
				fb_add_videomode(&vesa_modes[i],
						 &info->modelist);
		}

		/*
		 * default to resolution safe for projectors
		 * (since they are most common case without EDID)
		 */
		fb_vmode.xres = 800;
		fb_vmode.yres = 600;
		fb_vmode.refresh = 60;
		default_vmode = fb_find_nearest_mode(&fb_vmode,
						     &info->modelist);
	}

	/* If we have good mode and no active clients*/
	if ((default_vmode != NULL) && (dev->fb_count == 0)) {

		fb_videomode_to_var(&info->var, default_vmode);
		dlfb_var_color_format(&info->var);

		/*
		 * with mode size info, we can now alloc our framebuffer.
		 */
		memcpy(&info->fix, &dlfb_fix, sizeof(dlfb_fix));
		info->fix.line_length = info->var.xres *
			(info->var.bits_per_pixel / 8);

		result = dlfb_realloc_framebuffer(dev, info);

	} else
		result = -EINVAL;

error:
	if (edid && (dev->edid != edid))
		kfree(edid);

	if (info->dev)
		mutex_unlock(&info->lock);

	return result;
}

static ssize_t metrics_bytes_rendered_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_rendered));
}

static ssize_t metrics_bytes_identical_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_identical));
}

static ssize_t metrics_bytes_sent_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->bytes_sent));
}

static ssize_t metrics_cpu_kcycles_used_show(struct device *fbdev,
				   struct device_attribute *a, char *buf) {
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	return snprintf(buf, PAGE_SIZE, "%u\n",
			atomic_read(&dev->cpu_kcycles_used));
}

static ssize_t edid_show(
			struct file *filp,
			struct kobject *kobj, struct bin_attribute *a,
			 char *buf, loff_t off, size_t count) {
	struct device *fbdev = container_of(kobj, struct device, kobj);
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;

	if (dev->edid == NULL)
		return 0;

	if ((off >= dev->edid_size) || (count > dev->edid_size))
		return 0;

	if (off + count > dev->edid_size)
		count = dev->edid_size - off;

	pr_info("sysfs edid copy %p to %p, %d bytes\n",
		dev->edid, buf, (int) count);

	memcpy(buf, dev->edid, count);

	return count;
}

static ssize_t edid_store(
			struct file *filp,
			struct kobject *kobj, struct bin_attribute *a,
			char *src, loff_t src_off, size_t src_size) {
	struct device *fbdev = container_of(kobj, struct device, kobj);
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;
	int ret;

	/* We only support write of entire EDID at once, no offset*/
	if ((src_size != EDID_LENGTH) || (src_off != 0))
		return -EINVAL;

	ret = dlfb_setup_modes(dev, fb_info, src, src_size);
	if (ret)
		return ret;

	if (!dev->edid || memcmp(src, dev->edid, src_size))
		return -EINVAL;

	pr_info("sysfs written EDID is new default\n");
	dlfb_ops_set_par(fb_info);
	return src_size;
}

static ssize_t metrics_reset_store(struct device *fbdev,
			   struct device_attribute *attr,
			   const char *buf, size_t count)
{
	struct fb_info *fb_info = dev_get_drvdata(fbdev);
	struct dlfb_data *dev = fb_info->par;

	atomic_set(&dev->bytes_rendered, 0);
	atomic_set(&dev->bytes_identical, 0);
	atomic_set(&dev->bytes_sent, 0);
	atomic_set(&dev->cpu_kcycles_used, 0);

	return count;
}

static struct bin_attribute edid_attr = {
	.attr.name = "edid",
	.attr.mode = 0666,
	.size = EDID_LENGTH,
	.read = edid_show,
	.write = edid_store
};

static struct device_attribute fb_device_attrs[] = {
	__ATTR_RO(metrics_bytes_rendered),
	__ATTR_RO(metrics_bytes_identical),
	__ATTR_RO(metrics_bytes_sent),
	__ATTR_RO(metrics_cpu_kcycles_used),
	__ATTR(metrics_reset, S_IWUSR, NULL, metrics_reset_store),
};

/*
 * This is necessary before we can communicate with the display controller.
 */
static int dlfb_select_std_channel(struct dlfb_data *dev)
{
	int ret;
	void *buf;
	static const u8 set_def_chn[] = {
				0x57, 0xCD, 0xDC, 0xA7,
				0x1C, 0x88, 0x5E, 0x15,
				0x60, 0xFE, 0xC6, 0x97,
				0x16, 0x3D, 0x47, 0xF2  };

	buf = kmemdup(set_def_chn, sizeof(set_def_chn), GFP_KERNEL);

	if (!buf)
		return -ENOMEM;

	ret = usb_control_msg(dev->udev, usb_sndctrlpipe(dev->udev, 0),
			NR_USB_REQUEST_CHANNEL,
			(USB_DIR_OUT | USB_TYPE_VENDOR), 0, 0,
			buf, sizeof(set_def_chn), USB_CTRL_SET_TIMEOUT);

	kfree(buf);

	return ret;
}

static int dlfb_parse_vendor_descriptor(struct dlfb_data *dev,
					struct usb_interface *interface)
{
	char *desc;
	char *buf;
	char *desc_end;
	int total_len;

	buf = kzalloc(MAX_VENDOR_DESCRIPTOR_SIZE, GFP_KERNEL);
	if (!buf)
		return false;
	desc = buf;

	total_len = usb_get_descriptor(interface_to_usbdev(interface),
					0x5f, /* vendor specific */
					0, desc, MAX_VENDOR_DESCRIPTOR_SIZE);

	/* if not found, look in configuration descriptor */
	if (total_len < 0) {
		if (0 == usb_get_extra_descriptor(interface->cur_altsetting,
			0x5f, &desc))
			total_len = (int) desc[0];
	}

	if (total_len > 5) {
		pr_info("vendor descriptor length:%x data:%11ph\n", total_len,
			desc);

		if ((desc[0] != total_len) || /* descriptor length */
		    (desc[1] != 0x5f) ||   /* vendor descriptor type */
		    (desc[2] != 0x01) ||   /* version (2 bytes) */
		    (desc[3] != 0x00) ||
		    (desc[4] != total_len - 2)) /* length after type */
			goto unrecognized;

		desc_end = desc + total_len;
		desc += 5; /* the fixed header we've already parsed */

		while (desc < desc_end) {
			u8 length;
			u16 key;

			key = le16_to_cpu(*((u16 *) desc));
			desc += sizeof(u16);
			length = *desc;
			desc++;

			switch (key) {
			case 0x0200: { /* max_area */
				u32 max_area;
				max_area = le32_to_cpu(*((u32 *)desc));
				pr_warn("DL chip limited to %d pixel modes\n",
					max_area);
				dev->sku_pixel_limit = max_area;
				break;
			}
			default:
				break;
			}
			desc += length;
		}
	} else {
		pr_info("vendor descriptor not available (%d)\n", total_len);
	}

	goto success;

unrecognized:
	/* allow udlfb to load for now even if firmware unrecognized */
	pr_err("Unrecognized vendor firmware descriptor\n");

success:
	kfree(buf);
	return true;
}

static void dlfb_init_framebuffer_work(struct work_struct *work);

static int dlfb_usb_probe(struct usb_interface *interface,
			const struct usb_device_id *id)
{
	struct usb_device *usbdev;
	struct dlfb_data *dev;
	int retval = -ENOMEM;

	/* usb initialization */

	usbdev = interface_to_usbdev(interface);

	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
	if (dev == NULL) {
		dev_err(&interface->dev, "dlfb_usb_probe: failed alloc of dev struct\n");
		goto error;
	}

	kref_init(&dev->kref); /* matching kref_put in usb .disconnect fn */

	dev->udev = usbdev;
	dev->gdev = &usbdev->dev; /* our generic struct device * */
	usb_set_intfdata(interface, dev);

	pr_info("%s %s - serial #%s\n",
		usbdev->manufacturer, usbdev->product, usbdev->serial);
	pr_info("vid_%04x&pid_%04x&rev_%04x driver's dlfb_data struct at %p\n",
		le16_to_cpu(usbdev->descriptor.idVendor),
		le16_to_cpu(usbdev->descriptor.idProduct),
		le16_to_cpu(usbdev->descriptor.bcdDevice), dev);
	pr_info("console enable=%d\n", console);
	pr_info("fb_defio enable=%d\n", fb_defio);
	pr_info("shadow enable=%d\n", shadow);

	dev->sku_pixel_limit = 2048 * 1152; /* default to maximum */

	if (!dlfb_parse_vendor_descriptor(dev, interface)) {
		pr_err("firmware not recognized. Assume incompatible device\n");
		goto error;
	}

	if (pixel_limit) {
		pr_warn("DL chip limit of %d overridden"
			" by module param to %d\n",
			dev->sku_pixel_limit, pixel_limit);
		dev->sku_pixel_limit = pixel_limit;
	}


	if (!dlfb_alloc_urb_list(dev, WRITES_IN_FLIGHT, MAX_TRANSFER)) {
		retval = -ENOMEM;
		pr_err("dlfb_alloc_urb_list failed\n");
		goto error;
	}

	kref_get(&dev->kref); /* matching kref_put in free_framebuffer_work */

	/* We don't register a new USB class. Our client interface is fbdev */

	/* Workitem keep things fast & simple during USB enumeration */
	INIT_DELAYED_WORK(&dev->init_framebuffer_work,
			  dlfb_init_framebuffer_work);
	schedule_delayed_work(&dev->init_framebuffer_work, 0);

	return 0;

error:
	if (dev) {

		kref_put(&dev->kref, dlfb_free); /* ref for framebuffer */
		kref_put(&dev->kref, dlfb_free); /* last ref from kref_init */

		/* dev has been deallocated. Do not dereference */
	}

	return retval;
}

static void dlfb_init_framebuffer_work(struct work_struct *work)
{
	struct dlfb_data *dev = container_of(work, struct dlfb_data,
					     init_framebuffer_work.work);
	struct fb_info *info;
	int retval;
	int i;

	/* allocates framebuffer driver structure, not framebuffer memory */
	info = framebuffer_alloc(0, dev->gdev);
	if (!info) {
		pr_err("framebuffer_alloc failed\n");
		goto error;
	}

	dev->info = info;
	info->par = dev;
	info->pseudo_palette = dev->pseudo_palette;
	info->fbops = &dlfb_ops;

	retval = fb_alloc_cmap(&info->cmap, 256, 0);
	if (retval < 0) {
		pr_err("fb_alloc_cmap failed %x\n", retval);
		goto error;
	}

	INIT_DELAYED_WORK(&dev->free_framebuffer_work,
			  dlfb_free_framebuffer_work);

	INIT_LIST_HEAD(&info->modelist);

	retval = dlfb_setup_modes(dev, info, NULL, 0);
	if (retval != 0) {
		pr_err("unable to find common mode for display and adapter\n");
		goto error;
	}

	/* ready to begin using device */

	atomic_set(&dev->usb_active, 1);
	dlfb_select_std_channel(dev);

	dlfb_ops_check_var(&info->var, info);
	dlfb_ops_set_par(info);

	retval = register_framebuffer(info);
	if (retval < 0) {
		pr_err("register_framebuffer failed %d\n", retval);
		goto error;
	}

	for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++) {
		retval = device_create_file(info->dev, &fb_device_attrs[i]);
		if (retval) {
			pr_warn("device_create_file failed %d\n", retval);
		}
	}

	retval = device_create_bin_file(info->dev, &edid_attr);
	if (retval) {
		pr_warn("device_create_bin_file failed %d\n", retval);
	}

	pr_info("DisplayLink USB device /dev/fb%d attached. %dx%d resolution."
			" Using %dK framebuffer memory\n", info->node,
			info->var.xres, info->var.yres,
			((dev->backing_buffer) ?
			info->fix.smem_len * 2 : info->fix.smem_len) >> 10);
	return;

error:
	dlfb_free_framebuffer(dev);
}

static void dlfb_usb_disconnect(struct usb_interface *interface)
{
	struct dlfb_data *dev;
	struct fb_info *info;
	int i;

	dev = usb_get_intfdata(interface);
	info = dev->info;

	pr_info("USB disconnect starting\n");

	/* we virtualize until all fb clients release. Then we free */
	dev->virtualized = true;

	/* When non-active we'll update virtual framebuffer, but no new urbs */
	atomic_set(&dev->usb_active, 0);

	/* this function will wait for all in-flight urbs to complete */
	dlfb_free_urb_list(dev);

	if (info) {
		/* remove udlfb's sysfs interfaces */
		for (i = 0; i < ARRAY_SIZE(fb_device_attrs); i++)
			device_remove_file(info->dev, &fb_device_attrs[i]);
		device_remove_bin_file(info->dev, &edid_attr);
		unlink_framebuffer(info);
	}

	usb_set_intfdata(interface, NULL);
	dev->udev = NULL;
	dev->gdev = NULL;

	/* if clients still have us open, will be freed on last close */
	if (dev->fb_count == 0)
		schedule_delayed_work(&dev->free_framebuffer_work, 0);

	/* release reference taken by kref_init in probe() */
	kref_put(&dev->kref, dlfb_free);

	/* consider dlfb_data freed */

	return;
}

static struct usb_driver dlfb_driver = {
	.name = "udlfb",
	.probe = dlfb_usb_probe,
	.disconnect = dlfb_usb_disconnect,
	.id_table = id_table,
};

module_usb_driver(dlfb_driver);

static void dlfb_urb_completion(struct urb *urb)
{
	struct urb_node *unode = urb->context;
	struct dlfb_data *dev = unode->dev;
	unsigned long flags;

	/* sync/async unlink faults aren't errors */
	if (urb->status) {
		if (!(urb->status == -ENOENT ||
		    urb->status == -ECONNRESET ||
		    urb->status == -ESHUTDOWN)) {
			pr_err("%s - nonzero write bulk status received: %d\n",
				__func__, urb->status);
			atomic_set(&dev->lost_pixels, 1);
		}
	}

	urb->transfer_buffer_length = dev->urbs.size; /* reset to actual */

	spin_lock_irqsave(&dev->urbs.lock, flags);
	list_add_tail(&unode->entry, &dev->urbs.list);
	dev->urbs.available++;
	spin_unlock_irqrestore(&dev->urbs.lock, flags);

	/*
	 * When using fb_defio, we deadlock if up() is called
	 * while another is waiting. So queue to another process.
	 */
	if (fb_defio)
		schedule_delayed_work(&unode->release_urb_work, 0);
	else
		up(&dev->urbs.limit_sem);
}

static void dlfb_free_urb_list(struct dlfb_data *dev)
{
	int count = dev->urbs.count;
	struct list_head *node;
	struct urb_node *unode;
	struct urb *urb;
	int ret;
	unsigned long flags;

	pr_notice("Freeing all render urbs\n");

	/* keep waiting and freeing, until we've got 'em all */
	while (count--) {

		/* Getting interrupted means a leak, but ok at disconnect */
		ret = down_interruptible(&dev->urbs.limit_sem);
		if (ret)
			break;

		spin_lock_irqsave(&dev->urbs.lock, flags);

		node = dev->urbs.list.next; /* have reserved one with sem */
		list_del_init(node);

		spin_unlock_irqrestore(&dev->urbs.lock, flags);

		unode = list_entry(node, struct urb_node, entry);
		urb = unode->urb;

		/* Free each separately allocated piece */
		usb_free_coherent(urb->dev, dev->urbs.size,
				  urb->transfer_buffer, urb->transfer_dma);
		usb_free_urb(urb);
		kfree(node);
	}

	dev->urbs.count = 0;
}

static int dlfb_alloc_urb_list(struct dlfb_data *dev, int count, size_t size)
{
	int i = 0;
	struct urb *urb;
	struct urb_node *unode;
	char *buf;

	spin_lock_init(&dev->urbs.lock);

	dev->urbs.size = size;
	INIT_LIST_HEAD(&dev->urbs.list);

	while (i < count) {
		unode = kzalloc(sizeof(struct urb_node), GFP_KERNEL);
		if (!unode)
			break;
		unode->dev = dev;

		INIT_DELAYED_WORK(&unode->release_urb_work,
			  dlfb_release_urb_work);

		urb = usb_alloc_urb(0, GFP_KERNEL);
		if (!urb) {
			kfree(unode);
			break;
		}
		unode->urb = urb;

		buf = usb_alloc_coherent(dev->udev, MAX_TRANSFER, GFP_KERNEL,
					 &urb->transfer_dma);
		if (!buf) {
			kfree(unode);
			usb_free_urb(urb);
			break;
		}

		/* urb->transfer_buffer_length set to actual before submit */
		usb_fill_bulk_urb(urb, dev->udev, usb_sndbulkpipe(dev->udev, 1),
			buf, size, dlfb_urb_completion, unode);
		urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;

		list_add_tail(&unode->entry, &dev->urbs.list);

		i++;
	}

	sema_init(&dev->urbs.limit_sem, i);
	dev->urbs.count = i;
	dev->urbs.available = i;

	pr_notice("allocated %d %d byte urbs\n", i, (int) size);

	return i;
}

static struct urb *dlfb_get_urb(struct dlfb_data *dev)
{
	int ret;
	struct list_head *entry;
	struct urb_node *unode;
	struct urb *urb = NULL;
	unsigned long flags;

	/* Wait for an in-flight buffer to complete and get re-queued */
	ret = down_timeout(&dev->urbs.limit_sem, GET_URB_TIMEOUT);
	if (ret) {
		atomic_set(&dev->lost_pixels, 1);
		pr_warn("wait for urb interrupted: %x available: %d\n",
		       ret, dev->urbs.available);
		goto error;
	}

	spin_lock_irqsave(&dev->urbs.lock, flags);

	BUG_ON(list_empty(&dev->urbs.list)); /* reserved one with limit_sem */
	entry = dev->urbs.list.next;
	list_del_init(entry);
	dev->urbs.available--;

	spin_unlock_irqrestore(&dev->urbs.lock, flags);

	unode = list_entry(entry, struct urb_node, entry);
	urb = unode->urb;

error:
	return urb;
}

static int dlfb_submit_urb(struct dlfb_data *dev, struct urb *urb, size_t len)
{
	int ret;

	BUG_ON(len > dev->urbs.size);

	urb->transfer_buffer_length = len; /* set to actual payload len */
	ret = usb_submit_urb(urb, GFP_KERNEL);
	if (ret) {
		dlfb_urb_completion(urb); /* because no one else will */
		atomic_set(&dev->lost_pixels, 1);
		pr_err("usb_submit_urb error %x\n", ret);
	}
	return ret;
}

module_param(console, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
MODULE_PARM_DESC(console, "Allow fbcon to open framebuffer");

module_param(fb_defio, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
MODULE_PARM_DESC(fb_defio, "Page fault detection of mmap writes");

module_param(shadow, bool, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
MODULE_PARM_DESC(shadow, "Shadow vid mem. Disable to save mem but lose perf");

module_param(pixel_limit, int, S_IWUSR | S_IRUSR | S_IWGRP | S_IRGRP);
MODULE_PARM_DESC(pixel_limit, "Force limit on max mode (in x*y pixels)");

MODULE_AUTHOR("Roberto De Ioris <roberto@unbit.it>, "
	      "Jaya Kumar <jayakumar.lkml@gmail.com>, "
	      "Bernie Thompson <bernie@plugable.com>");
MODULE_DESCRIPTION("DisplayLink kernel framebuffer driver");
MODULE_LICENSE("GPL");