linux/drivers/usb/storage/scsiglue.c
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   1/*
   2 * Driver for USB Mass Storage compliant devices
   3 * SCSI layer glue code
   4 *
   5 * Current development and maintenance by:
   6 *   (c) 1999-2002 Matthew Dharm (mdharm-usb@one-eyed-alien.net)
   7 *
   8 * Developed with the assistance of:
   9 *   (c) 2000 David L. Brown, Jr. (usb-storage@davidb.org)
  10 *   (c) 2000 Stephen J. Gowdy (SGowdy@lbl.gov)
  11 *
  12 * Initial work by:
  13 *   (c) 1999 Michael Gee (michael@linuxspecific.com)
  14 *
  15 * This driver is based on the 'USB Mass Storage Class' document. This
  16 * describes in detail the protocol used to communicate with such
  17 * devices.  Clearly, the designers had SCSI and ATAPI commands in
  18 * mind when they created this document.  The commands are all very
  19 * similar to commands in the SCSI-II and ATAPI specifications.
  20 *
  21 * It is important to note that in a number of cases this class
  22 * exhibits class-specific exemptions from the USB specification.
  23 * Notably the usage of NAK, STALL and ACK differs from the norm, in
  24 * that they are used to communicate wait, failed and OK on commands.
  25 *
  26 * Also, for certain devices, the interrupt endpoint is used to convey
  27 * status of a command.
  28 *
  29 * Please see http://www.one-eyed-alien.net/~mdharm/linux-usb for more
  30 * information about this driver.
  31 *
  32 * This program is free software; you can redistribute it and/or modify it
  33 * under the terms of the GNU General Public License as published by the
  34 * Free Software Foundation; either version 2, or (at your option) any
  35 * later version.
  36 *
  37 * This program is distributed in the hope that it will be useful, but
  38 * WITHOUT ANY WARRANTY; without even the implied warranty of
  39 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  40 * General Public License for more details.
  41 *
  42 * You should have received a copy of the GNU General Public License along
  43 * with this program; if not, write to the Free Software Foundation, Inc.,
  44 * 675 Mass Ave, Cambridge, MA 02139, USA.
  45 */
  46
  47#include <linux/module.h>
  48#include <linux/mutex.h>
  49
  50#include <scsi/scsi.h>
  51#include <scsi/scsi_cmnd.h>
  52#include <scsi/scsi_devinfo.h>
  53#include <scsi/scsi_device.h>
  54#include <scsi/scsi_eh.h>
  55
  56#include "usb.h"
  57#include "scsiglue.h"
  58#include "debug.h"
  59#include "transport.h"
  60#include "protocol.h"
  61
  62/*
  63 * Vendor IDs for companies that seem to include the READ CAPACITY bug
  64 * in all their devices
  65 */
  66#define VENDOR_ID_NOKIA         0x0421
  67#define VENDOR_ID_NIKON         0x04b0
  68#define VENDOR_ID_PENTAX        0x0a17
  69#define VENDOR_ID_MOTOROLA      0x22b8
  70
  71/***********************************************************************
  72 * Host functions 
  73 ***********************************************************************/
  74
  75static const char* host_info(struct Scsi_Host *host)
  76{
  77        struct us_data *us = host_to_us(host);
  78        return us->scsi_name;
  79}
  80
  81static int slave_alloc (struct scsi_device *sdev)
  82{
  83        struct us_data *us = host_to_us(sdev->host);
  84
  85        /*
  86         * Set the INQUIRY transfer length to 36.  We don't use any of
  87         * the extra data and many devices choke if asked for more or
  88         * less than 36 bytes.
  89         */
  90        sdev->inquiry_len = 36;
  91
  92        /*
  93         * USB has unusual DMA-alignment requirements: Although the
  94         * starting address of each scatter-gather element doesn't matter,
  95         * the length of each element except the last must be divisible
  96         * by the Bulk maxpacket value.  There's currently no way to
  97         * express this by block-layer constraints, so we'll cop out
  98         * and simply require addresses to be aligned at 512-byte
  99         * boundaries.  This is okay since most block I/O involves
 100         * hardware sectors that are multiples of 512 bytes in length,
 101         * and since host controllers up through USB 2.0 have maxpacket
 102         * values no larger than 512.
 103         *
 104         * But it doesn't suffice for Wireless USB, where Bulk maxpacket
 105         * values can be as large as 2048.  To make that work properly
 106         * will require changes to the block layer.
 107         */
 108        blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));
 109
 110        /* Tell the SCSI layer if we know there is more than one LUN */
 111        if (us->protocol == USB_PR_BULK && us->max_lun > 0)
 112                sdev->sdev_bflags |= BLIST_FORCELUN;
 113
 114        return 0;
 115}
 116
 117static int slave_configure(struct scsi_device *sdev)
 118{
 119        struct us_data *us = host_to_us(sdev->host);
 120
 121        /*
 122         * Many devices have trouble transferring more than 32KB at a time,
 123         * while others have trouble with more than 64K. At this time we
 124         * are limiting both to 32K (64 sectores).
 125         */
 126        if (us->fflags & (US_FL_MAX_SECTORS_64 | US_FL_MAX_SECTORS_MIN)) {
 127                unsigned int max_sectors = 64;
 128
 129                if (us->fflags & US_FL_MAX_SECTORS_MIN)
 130                        max_sectors = PAGE_CACHE_SIZE >> 9;
 131                if (queue_max_hw_sectors(sdev->request_queue) > max_sectors)
 132                        blk_queue_max_hw_sectors(sdev->request_queue,
 133                                              max_sectors);
 134        } else if (sdev->type == TYPE_TAPE) {
 135                /*
 136                 * Tapes need much higher max_sector limits, so just
 137                 * raise it to the maximum possible (4 GB / 512) and
 138                 * let the queue segment size sort out the real limit.
 139                 */
 140                blk_queue_max_hw_sectors(sdev->request_queue, 0x7FFFFF);
 141        } else if (us->pusb_dev->speed >= USB_SPEED_SUPER) {
 142                /*
 143                 * USB3 devices will be limited to 2048 sectors. This gives us
 144                 * better throughput on most devices.
 145                 */
 146                blk_queue_max_hw_sectors(sdev->request_queue, 2048);
 147        }
 148
 149        /*
 150         * Some USB host controllers can't do DMA; they have to use PIO.
 151         * They indicate this by setting their dma_mask to NULL.  For
 152         * such controllers we need to make sure the block layer sets
 153         * up bounce buffers in addressable memory.
 154         */
 155        if (!us->pusb_dev->bus->controller->dma_mask)
 156                blk_queue_bounce_limit(sdev->request_queue, BLK_BOUNCE_HIGH);
 157
 158        /*
 159         * We can't put these settings in slave_alloc() because that gets
 160         * called before the device type is known.  Consequently these
 161         * settings can't be overridden via the scsi devinfo mechanism.
 162         */
 163        if (sdev->type == TYPE_DISK) {
 164
 165                /*
 166                 * Some vendors seem to put the READ CAPACITY bug into
 167                 * all their devices -- primarily makers of cell phones
 168                 * and digital cameras.  Since these devices always use
 169                 * flash media and can be expected to have an even number
 170                 * of sectors, we will always enable the CAPACITY_HEURISTICS
 171                 * flag unless told otherwise.
 172                 */
 173                switch (le16_to_cpu(us->pusb_dev->descriptor.idVendor)) {
 174                case VENDOR_ID_NOKIA:
 175                case VENDOR_ID_NIKON:
 176                case VENDOR_ID_PENTAX:
 177                case VENDOR_ID_MOTOROLA:
 178                        if (!(us->fflags & (US_FL_FIX_CAPACITY |
 179                                        US_FL_CAPACITY_OK)))
 180                                us->fflags |= US_FL_CAPACITY_HEURISTICS;
 181                        break;
 182                }
 183
 184                /*
 185                 * Disk-type devices use MODE SENSE(6) if the protocol
 186                 * (SubClass) is Transparent SCSI, otherwise they use
 187                 * MODE SENSE(10).
 188                 */
 189                if (us->subclass != USB_SC_SCSI && us->subclass != USB_SC_CYP_ATACB)
 190                        sdev->use_10_for_ms = 1;
 191
 192                /*
 193                 *Many disks only accept MODE SENSE transfer lengths of
 194                 * 192 bytes (that's what Windows uses).
 195                 */
 196                sdev->use_192_bytes_for_3f = 1;
 197
 198                /*
 199                 * Some devices don't like MODE SENSE with page=0x3f,
 200                 * which is the command used for checking if a device
 201                 * is write-protected.  Now that we tell the sd driver
 202                 * to do a 192-byte transfer with this command the
 203                 * majority of devices work fine, but a few still can't
 204                 * handle it.  The sd driver will simply assume those
 205                 * devices are write-enabled.
 206                 */
 207                if (us->fflags & US_FL_NO_WP_DETECT)
 208                        sdev->skip_ms_page_3f = 1;
 209
 210                /*
 211                 * A number of devices have problems with MODE SENSE for
 212                 * page x08, so we will skip it.
 213                 */
 214                sdev->skip_ms_page_8 = 1;
 215
 216                /* Some devices don't handle VPD pages correctly */
 217                sdev->skip_vpd_pages = 1;
 218
 219                /* Do not attempt to use REPORT SUPPORTED OPERATION CODES */
 220                sdev->no_report_opcodes = 1;
 221
 222                /* Do not attempt to use WRITE SAME */
 223                sdev->no_write_same = 1;
 224
 225                /*
 226                 * Some disks return the total number of blocks in response
 227                 * to READ CAPACITY rather than the highest block number.
 228                 * If this device makes that mistake, tell the sd driver.
 229                 */
 230                if (us->fflags & US_FL_FIX_CAPACITY)
 231                        sdev->fix_capacity = 1;
 232
 233                /*
 234                 * A few disks have two indistinguishable version, one of
 235                 * which reports the correct capacity and the other does not.
 236                 * The sd driver has to guess which is the case.
 237                 */
 238                if (us->fflags & US_FL_CAPACITY_HEURISTICS)
 239                        sdev->guess_capacity = 1;
 240
 241                /* Some devices cannot handle READ_CAPACITY_16 */
 242                if (us->fflags & US_FL_NO_READ_CAPACITY_16)
 243                        sdev->no_read_capacity_16 = 1;
 244
 245                /*
 246                 * Many devices do not respond properly to READ_CAPACITY_16.
 247                 * Tell the SCSI layer to try READ_CAPACITY_10 first.
 248                 * However some USB 3.0 drive enclosures return capacity
 249                 * modulo 2TB. Those must use READ_CAPACITY_16
 250                 */
 251                if (!(us->fflags & US_FL_NEEDS_CAP16))
 252                        sdev->try_rc_10_first = 1;
 253
 254                /* assume SPC3 or latter devices support sense size > 18 */
 255                if (sdev->scsi_level > SCSI_SPC_2)
 256                        us->fflags |= US_FL_SANE_SENSE;
 257
 258                /*
 259                 * USB-IDE bridges tend to report SK = 0x04 (Non-recoverable
 260                 * Hardware Error) when any low-level error occurs,
 261                 * recoverable or not.  Setting this flag tells the SCSI
 262                 * midlayer to retry such commands, which frequently will
 263                 * succeed and fix the error.  The worst this can lead to
 264                 * is an occasional series of retries that will all fail.
 265                 */
 266                sdev->retry_hwerror = 1;
 267
 268                /*
 269                 * USB disks should allow restart.  Some drives spin down
 270                 * automatically, requiring a START-STOP UNIT command.
 271                 */
 272                sdev->allow_restart = 1;
 273
 274                /*
 275                 * Some USB cardreaders have trouble reading an sdcard's last
 276                 * sector in a larger then 1 sector read, since the performance
 277                 * impact is negligible we set this flag for all USB disks
 278                 */
 279                sdev->last_sector_bug = 1;
 280
 281                /*
 282                 * Enable last-sector hacks for single-target devices using
 283                 * the Bulk-only transport, unless we already know the
 284                 * capacity will be decremented or is correct.
 285                 */
 286                if (!(us->fflags & (US_FL_FIX_CAPACITY | US_FL_CAPACITY_OK |
 287                                        US_FL_SCM_MULT_TARG)) &&
 288                                us->protocol == USB_PR_BULK)
 289                        us->use_last_sector_hacks = 1;
 290
 291                /* Check if write cache default on flag is set or not */
 292                if (us->fflags & US_FL_WRITE_CACHE)
 293                        sdev->wce_default_on = 1;
 294
 295                /* A few buggy USB-ATA bridges don't understand FUA */
 296                if (us->fflags & US_FL_BROKEN_FUA)
 297                        sdev->broken_fua = 1;
 298
 299                /* Some even totally fail to indicate a cache */
 300                if (us->fflags & US_FL_ALWAYS_SYNC) {
 301                        /* don't read caching information */
 302                        sdev->skip_ms_page_8 = 1;
 303                        sdev->skip_ms_page_3f = 1;
 304                        /* assume sync is needed */
 305                        sdev->wce_default_on = 1;
 306                }
 307        } else {
 308
 309                /*
 310                 * Non-disk-type devices don't need to blacklist any pages
 311                 * or to force 192-byte transfer lengths for MODE SENSE.
 312                 * But they do need to use MODE SENSE(10).
 313                 */
 314                sdev->use_10_for_ms = 1;
 315
 316                /* Some (fake) usb cdrom devices don't like READ_DISC_INFO */
 317                if (us->fflags & US_FL_NO_READ_DISC_INFO)
 318                        sdev->no_read_disc_info = 1;
 319        }
 320
 321        /*
 322         * The CB and CBI transports have no way to pass LUN values
 323         * other than the bits in the second byte of a CDB.  But those
 324         * bits don't get set to the LUN value if the device reports
 325         * scsi_level == 0 (UNKNOWN).  Hence such devices must necessarily
 326         * be single-LUN.
 327         */
 328        if ((us->protocol == USB_PR_CB || us->protocol == USB_PR_CBI) &&
 329                        sdev->scsi_level == SCSI_UNKNOWN)
 330                us->max_lun = 0;
 331
 332        /*
 333         * Some devices choke when they receive a PREVENT-ALLOW MEDIUM
 334         * REMOVAL command, so suppress those commands.
 335         */
 336        if (us->fflags & US_FL_NOT_LOCKABLE)
 337                sdev->lockable = 0;
 338
 339        /*
 340         * this is to satisfy the compiler, tho I don't think the 
 341         * return code is ever checked anywhere.
 342         */
 343        return 0;
 344}
 345
 346static int target_alloc(struct scsi_target *starget)
 347{
 348        struct us_data *us = host_to_us(dev_to_shost(starget->dev.parent));
 349
 350        /*
 351         * Some USB drives don't support REPORT LUNS, even though they
 352         * report a SCSI revision level above 2.  Tell the SCSI layer
 353         * not to issue that command; it will perform a normal sequential
 354         * scan instead.
 355         */
 356        starget->no_report_luns = 1;
 357
 358        /*
 359         * The UFI spec treats the Peripheral Qualifier bits in an
 360         * INQUIRY result as reserved and requires devices to set them
 361         * to 0.  However the SCSI spec requires these bits to be set
 362         * to 3 to indicate when a LUN is not present.
 363         *
 364         * Let the scanning code know if this target merely sets
 365         * Peripheral Device Type to 0x1f to indicate no LUN.
 366         */
 367        if (us->subclass == USB_SC_UFI)
 368                starget->pdt_1f_for_no_lun = 1;
 369
 370        return 0;
 371}
 372
 373/* queue a command */
 374/* This is always called with scsi_lock(host) held */
 375static int queuecommand_lck(struct scsi_cmnd *srb,
 376                        void (*done)(struct scsi_cmnd *))
 377{
 378        struct us_data *us = host_to_us(srb->device->host);
 379
 380        /* check for state-transition errors */
 381        if (us->srb != NULL) {
 382                printk(KERN_ERR USB_STORAGE "Error in %s: us->srb = %p\n",
 383                        __func__, us->srb);
 384                return SCSI_MLQUEUE_HOST_BUSY;
 385        }
 386
 387        /* fail the command if we are disconnecting */
 388        if (test_bit(US_FLIDX_DISCONNECTING, &us->dflags)) {
 389                usb_stor_dbg(us, "Fail command during disconnect\n");
 390                srb->result = DID_NO_CONNECT << 16;
 391                done(srb);
 392                return 0;
 393        }
 394
 395        /* enqueue the command and wake up the control thread */
 396        srb->scsi_done = done;
 397        us->srb = srb;
 398        complete(&us->cmnd_ready);
 399
 400        return 0;
 401}
 402
 403static DEF_SCSI_QCMD(queuecommand)
 404
 405/***********************************************************************
 406 * Error handling functions
 407 ***********************************************************************/
 408
 409/* Command timeout and abort */
 410static int command_abort(struct scsi_cmnd *srb)
 411{
 412        struct us_data *us = host_to_us(srb->device->host);
 413
 414        usb_stor_dbg(us, "%s called\n", __func__);
 415
 416        /*
 417         * us->srb together with the TIMED_OUT, RESETTING, and ABORTING
 418         * bits are protected by the host lock.
 419         */
 420        scsi_lock(us_to_host(us));
 421
 422        /* Is this command still active? */
 423        if (us->srb != srb) {
 424                scsi_unlock(us_to_host(us));
 425                usb_stor_dbg(us, "-- nothing to abort\n");
 426                return FAILED;
 427        }
 428
 429        /*
 430         * Set the TIMED_OUT bit.  Also set the ABORTING bit, but only if
 431         * a device reset isn't already in progress (to avoid interfering
 432         * with the reset).  Note that we must retain the host lock while
 433         * calling usb_stor_stop_transport(); otherwise it might interfere
 434         * with an auto-reset that begins as soon as we release the lock.
 435         */
 436        set_bit(US_FLIDX_TIMED_OUT, &us->dflags);
 437        if (!test_bit(US_FLIDX_RESETTING, &us->dflags)) {
 438                set_bit(US_FLIDX_ABORTING, &us->dflags);
 439                usb_stor_stop_transport(us);
 440        }
 441        scsi_unlock(us_to_host(us));
 442
 443        /* Wait for the aborted command to finish */
 444        wait_for_completion(&us->notify);
 445        return SUCCESS;
 446}
 447
 448/*
 449 * This invokes the transport reset mechanism to reset the state of the
 450 * device
 451 */
 452static int device_reset(struct scsi_cmnd *srb)
 453{
 454        struct us_data *us = host_to_us(srb->device->host);
 455        int result;
 456
 457        usb_stor_dbg(us, "%s called\n", __func__);
 458
 459        /* lock the device pointers and do the reset */
 460        mutex_lock(&(us->dev_mutex));
 461        result = us->transport_reset(us);
 462        mutex_unlock(&us->dev_mutex);
 463
 464        return result < 0 ? FAILED : SUCCESS;
 465}
 466
 467/* Simulate a SCSI bus reset by resetting the device's USB port. */
 468static int bus_reset(struct scsi_cmnd *srb)
 469{
 470        struct us_data *us = host_to_us(srb->device->host);
 471        int result;
 472
 473        usb_stor_dbg(us, "%s called\n", __func__);
 474
 475        result = usb_stor_port_reset(us);
 476        return result < 0 ? FAILED : SUCCESS;
 477}
 478
 479/*
 480 * Report a driver-initiated device reset to the SCSI layer.
 481 * Calling this for a SCSI-initiated reset is unnecessary but harmless.
 482 * The caller must own the SCSI host lock.
 483 */
 484void usb_stor_report_device_reset(struct us_data *us)
 485{
 486        int i;
 487        struct Scsi_Host *host = us_to_host(us);
 488
 489        scsi_report_device_reset(host, 0, 0);
 490        if (us->fflags & US_FL_SCM_MULT_TARG) {
 491                for (i = 1; i < host->max_id; ++i)
 492                        scsi_report_device_reset(host, 0, i);
 493        }
 494}
 495
 496/*
 497 * Report a driver-initiated bus reset to the SCSI layer.
 498 * Calling this for a SCSI-initiated reset is unnecessary but harmless.
 499 * The caller must not own the SCSI host lock.
 500 */
 501void usb_stor_report_bus_reset(struct us_data *us)
 502{
 503        struct Scsi_Host *host = us_to_host(us);
 504
 505        scsi_lock(host);
 506        scsi_report_bus_reset(host, 0);
 507        scsi_unlock(host);
 508}
 509
 510/***********************************************************************
 511 * /proc/scsi/ functions
 512 ***********************************************************************/
 513
 514static int write_info(struct Scsi_Host *host, char *buffer, int length)
 515{
 516        /* if someone is sending us data, just throw it away */
 517        return length;
 518}
 519
 520static int show_info (struct seq_file *m, struct Scsi_Host *host)
 521{
 522        struct us_data *us = host_to_us(host);
 523        const char *string;
 524
 525        /* print the controller name */
 526        seq_printf(m, "   Host scsi%d: usb-storage\n", host->host_no);
 527
 528        /* print product, vendor, and serial number strings */
 529        if (us->pusb_dev->manufacturer)
 530                string = us->pusb_dev->manufacturer;
 531        else if (us->unusual_dev->vendorName)
 532                string = us->unusual_dev->vendorName;
 533        else
 534                string = "Unknown";
 535        seq_printf(m, "       Vendor: %s\n", string);
 536        if (us->pusb_dev->product)
 537                string = us->pusb_dev->product;
 538        else if (us->unusual_dev->productName)
 539                string = us->unusual_dev->productName;
 540        else
 541                string = "Unknown";
 542        seq_printf(m, "      Product: %s\n", string);
 543        if (us->pusb_dev->serial)
 544                string = us->pusb_dev->serial;
 545        else
 546                string = "None";
 547        seq_printf(m, "Serial Number: %s\n", string);
 548
 549        /* show the protocol and transport */
 550        seq_printf(m, "     Protocol: %s\n", us->protocol_name);
 551        seq_printf(m, "    Transport: %s\n", us->transport_name);
 552
 553        /* show the device flags */
 554        seq_printf(m, "       Quirks:");
 555
 556#define US_FLAG(name, value) \
 557        if (us->fflags & value) seq_printf(m, " " #name);
 558US_DO_ALL_FLAGS
 559#undef US_FLAG
 560        seq_putc(m, '\n');
 561        return 0;
 562}
 563
 564/***********************************************************************
 565 * Sysfs interface
 566 ***********************************************************************/
 567
 568/* Output routine for the sysfs max_sectors file */
 569static ssize_t max_sectors_show(struct device *dev, struct device_attribute *attr, char *buf)
 570{
 571        struct scsi_device *sdev = to_scsi_device(dev);
 572
 573        return sprintf(buf, "%u\n", queue_max_hw_sectors(sdev->request_queue));
 574}
 575
 576/* Input routine for the sysfs max_sectors file */
 577static ssize_t max_sectors_store(struct device *dev, struct device_attribute *attr, const char *buf,
 578                size_t count)
 579{
 580        struct scsi_device *sdev = to_scsi_device(dev);
 581        unsigned short ms;
 582
 583        if (sscanf(buf, "%hu", &ms) > 0) {
 584                blk_queue_max_hw_sectors(sdev->request_queue, ms);
 585                return count;
 586        }
 587        return -EINVAL;
 588}
 589static DEVICE_ATTR_RW(max_sectors);
 590
 591static struct device_attribute *sysfs_device_attr_list[] = {
 592        &dev_attr_max_sectors,
 593        NULL,
 594};
 595
 596/*
 597 * this defines our host template, with which we'll allocate hosts
 598 */
 599
 600static const struct scsi_host_template usb_stor_host_template = {
 601        /* basic userland interface stuff */
 602        .name =                         "usb-storage",
 603        .proc_name =                    "usb-storage",
 604        .show_info =                    show_info,
 605        .write_info =                   write_info,
 606        .info =                         host_info,
 607
 608        /* command interface -- queued only */
 609        .queuecommand =                 queuecommand,
 610
 611        /* error and abort handlers */
 612        .eh_abort_handler =             command_abort,
 613        .eh_device_reset_handler =      device_reset,
 614        .eh_bus_reset_handler =         bus_reset,
 615
 616        /* queue commands only, only one command per LUN */
 617        .can_queue =                    1,
 618        .cmd_per_lun =                  1,
 619
 620        /* unknown initiator id */
 621        .this_id =                      -1,
 622
 623        .slave_alloc =                  slave_alloc,
 624        .slave_configure =              slave_configure,
 625        .target_alloc =                 target_alloc,
 626
 627        /* lots of sg segments can be handled */
 628        .sg_tablesize =                 SCSI_MAX_SG_CHAIN_SEGMENTS,
 629
 630
 631        /*
 632         * Limit the total size of a transfer to 120 KB.
 633         *
 634         * Some devices are known to choke with anything larger. It seems like
 635         * the problem stems from the fact that original IDE controllers had
 636         * only an 8-bit register to hold the number of sectors in one transfer
 637         * and even those couldn't handle a full 256 sectors.
 638         *
 639         * Because we want to make sure we interoperate with as many devices as
 640         * possible, we will maintain a 240 sector transfer size limit for USB
 641         * Mass Storage devices.
 642         *
 643         * Tests show that other operating have similar limits with Microsoft
 644         * Windows 7 limiting transfers to 128 sectors for both USB2 and USB3
 645         * and Apple Mac OS X 10.11 limiting transfers to 256 sectors for USB2
 646         * and 2048 for USB3 devices.
 647         */
 648        .max_sectors =                  240,
 649
 650        /*
 651         * merge commands... this seems to help performance, but
 652         * periodically someone should test to see which setting is more
 653         * optimal.
 654         */
 655        .use_clustering =               1,
 656
 657        /* emulated HBA */
 658        .emulated =                     1,
 659
 660        /* we do our own delay after a device or bus reset */
 661        .skip_settle_delay =            1,
 662
 663        /* sysfs device attributes */
 664        .sdev_attrs =                   sysfs_device_attr_list,
 665
 666        /* module management */
 667        .module =                       THIS_MODULE
 668};
 669
 670void usb_stor_host_template_init(struct scsi_host_template *sht,
 671                                 const char *name, struct module *owner)
 672{
 673        *sht = usb_stor_host_template;
 674        sht->name = name;
 675        sht->proc_name = name;
 676        sht->module = owner;
 677}
 678EXPORT_SYMBOL_GPL(usb_stor_host_template_init);
 679
 680/* To Report "Illegal Request: Invalid Field in CDB */
 681unsigned char usb_stor_sense_invalidCDB[18] = {
 682        [0]     = 0x70,                     /* current error */
 683        [2]     = ILLEGAL_REQUEST,          /* Illegal Request = 0x05 */
 684        [7]     = 0x0a,                     /* additional length */
 685        [12]    = 0x24                      /* Invalid Field in CDB */
 686};
 687EXPORT_SYMBOL_GPL(usb_stor_sense_invalidCDB);
 688