drivers/spi/spidev.c

   1 /*
   2  * Simple synchronous userspace interface to SPI devices
   3  *
   4  * Copyright (C) 2006 SWAPP
   5  *      Andrea Paterniani <a.paterniani@swapp-eng.it>
   6  * Copyright (C) 2007 David Brownell (simplification, cleanup)
   7  *
   8  * This program is free software; you can redistribute it and/or modify
   9  * it under the terms of the GNU General Public License as published by
  10  * the Free Software Foundation; either version 2 of the License, or
  11  * (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, write to the Free Software
  20  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  21  */
  22
  23 #include <linux/init.h>
  24 #include <linux/module.h>
  25 #include <linux/ioctl.h>
  26 #include <linux/fs.h>
  27 #include <linux/device.h>
  28 #include <linux/err.h>
  29 #include <linux/list.h>
  30 #include <linux/errno.h>
  31 #include <linux/mutex.h>
  32 #include <linux/slab.h>
  33 #include <linux/compat.h>
  34
  35 #include <linux/spi/spi.h>
  36 #include <linux/spi/spidev.h>
  37
  38 #include <asm/uaccess.h>
  39
  40
  41 /*
  42  * This supports access to SPI devices using normal userspace I/O calls.
  43  * Note that while traditional UNIX/POSIX I/O semantics are half duplex,
  44  * and often mask message boundaries, full SPI support requires full duplex
  45  * transfers.  There are several kinds of internal message boundaries to
  46  * handle chipselect management and other protocol options.
  47  *
  48  * SPI has a character major number assigned.  We allocate minor numbers
  49  * dynamically using a bitmask.  You must use hotplug tools, such as udev
  50  * (or mdev with busybox) to create and destroy the /dev/spidevB.C device
  51  * nodes, since there is no fixed association of minor numbers with any
  52  * particular SPI bus or device.
  53  */
  54 #define SPIDEV_MAJOR                    153     /* assigned */
  55 #define N_SPI_MINORS                    32      /* ... up to 256 */
  56
  57 static DECLARE_BITMAP(minors, N_SPI_MINORS);
  58
  59
  60 /* Bit masks for spi_device.mode management.  Note that incorrect
  61  * settings for some settings can cause *lots* of trouble for other
  62  * devices on a shared bus:
  63  *
  64  *  - CS_HIGH ... this device will be active when it shouldn't be
  65  *  - 3WIRE ... when active, it won't behave as it should
  66  *  - NO_CS ... there will be no explicit message boundaries; this
  67  *      is completely incompatible with the shared bus model
  68  *  - READY ... transfers may proceed when they shouldn't.
  69  *
  70  * REVISIT should changing those flags be privileged?
  71  */
  72 #define SPI_MODE_MASK           (SPI_CPHA | SPI_CPOL | SPI_CS_HIGH \
  73                                 | SPI_LSB_FIRST | SPI_3WIRE | SPI_LOOP \
  74                                 | SPI_NO_CS | SPI_READY)
  75
  76 struct spidev_data {
  77         dev_t                   devt;
  78         spinlock_t              spi_lock;
  79         struct spi_device       *spi;
  80         struct list_head        device_entry;
  81
  82         /* buffer is NULL unless this device is open (users > 0) */
  83         struct mutex            buf_lock;
  84         unsigned                users;
  85         u8                      *buffer;
  86 };
  87
  88 static LIST_HEAD(device_list);
  89 static DEFINE_MUTEX(device_list_lock);
  90
  91 static unsigned bufsiz = 4096;
  92 module_param(bufsiz, uint, S_IRUGO);
  93 MODULE_PARM_DESC(bufsiz, "data bytes in biggest supported SPI message");
  94
  95 /*-------------------------------------------------------------------------*/
  96
  97 /*
  98  * We can't use the standard synchronous wrappers for file I/O; we
  99  * need to protect against async removal of the underlying spi_device.
 100  */
 101 static void spidev_complete(void *arg)
 102 {
 103         complete(arg);
 104 }
 105
 106 static ssize_t
 107 spidev_sync(struct spidev_data *spidev, struct spi_message *message)
 108 {
 109         DECLARE_COMPLETION_ONSTACK(done);
 110         int status;
 111
 112         message->complete = spidev_complete;
 113         message->context = &done;
 114
 115         spin_lock_irq(&spidev->spi_lock);
 116         if (spidev->spi == NULL)
 117                 status = -ESHUTDOWN;
 118         else
 119                 status = spi_async(spidev->spi, message);
 120         spin_unlock_irq(&spidev->spi_lock);
 121
 122         if (status == 0) {
 123                 wait_for_completion(&done);
 124                 status = message->status;
 125                 if (status == 0)
 126                         status = message->actual_length;
 127         }
 128         return status;
 129 }
 130
 131 static inline ssize_t
 132 spidev_sync_write(struct spidev_data *spidev, size_t len)
 133 {
 134         struct spi_transfer     t = {
 135                         .tx_buf         = spidev->buffer,
 136                         .len            = len,
 137                 };
 138         struct spi_message      m;
 139
 140         spi_message_init(&m);
 141         spi_message_add_tail(&t, &m);
 142         return spidev_sync(spidev, &m);
 143 }
 144
 145 static inline ssize_t
 146 spidev_sync_read(struct spidev_data *spidev, size_t len)
 147 {
 148         struct spi_transfer     t = {
 149                         .rx_buf         = spidev->buffer,
 150                         .len            = len,
 151                 };
 152         struct spi_message      m;
 153
 154         spi_message_init(&m);
 155         spi_message_add_tail(&t, &m);
 156         return spidev_sync(spidev, &m);
 157 }
 158
 159 /*-------------------------------------------------------------------------*/
 160
 161 /* Read-only message with current device setup */
 162 static ssize_t
 163 spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
 164 {
 165         struct spidev_data      *spidev;
 166         ssize_t                 status = 0;
 167
 168         /* chipselect only toggles at start or end of operation */
 169         if (count > bufsiz)
 170                 return -EMSGSIZE;
 171
 172         spidev = filp->private_data;
 173
 174         mutex_lock(&spidev->buf_lock);
 175         status = spidev_sync_read(spidev, count);
 176         if (status > 0) {
 177                 unsigned long   missing;
 178
 179                 missing = copy_to_user(buf, spidev->buffer, status);
 180                 if (missing == status)
 181                         status = -EFAULT;
 182                 else
 183                         status = status - missing;
 184         }
 185         mutex_unlock(&spidev->buf_lock);
 186
 187         return status;
 188 }
 189
 190 /* Write-only message with current device setup */
 191 static ssize_t
 192 spidev_write(struct file *filp, const char __user *buf,
 193                 size_t count, loff_t *f_pos)
 194 {
 195         struct spidev_data      *spidev;
 196         ssize_t                 status = 0;
 197         unsigned long           missing;
 198
 199         /* chipselect only toggles at start or end of operation */
 200         if (count > bufsiz)
 201                 return -EMSGSIZE;
 202
 203         spidev = filp->private_data;
 204
 205         mutex_lock(&spidev->buf_lock);
 206         missing = copy_from_user(spidev->buffer, buf, count);
 207         if (missing == 0) {
 208                 status = spidev_sync_write(spidev, count);
 209         } else
 210                 status = -EFAULT;
 211         mutex_unlock(&spidev->buf_lock);
 212
 213         return status;
 214 }
 215
 216 static int spidev_message(struct spidev_data *spidev,
 217                 struct spi_ioc_transfer *u_xfers, unsigned n_xfers)
 218 {
 219         struct spi_message      msg;
 220         struct spi_transfer     *k_xfers;
 221         struct spi_transfer     *k_tmp;
 222         struct spi_ioc_transfer *u_tmp;
 223         unsigned                n, total;
 224         u8                      *buf;
 225         int                     status = -EFAULT;
 226
 227         spi_message_init(&msg);
 228         k_xfers = kcalloc(n_xfers, sizeof(*k_tmp), GFP_KERNEL);
 229         if (k_xfers == NULL)
 230                 return -ENOMEM;
 231
 232         /* Construct spi_message, copying any tx data to bounce buffer.
 233          * We walk the array of user-provided transfers, using each one
 234          * to initialize a kernel version of the same transfer.
 235          */
 236         buf = spidev->buffer;
 237         total = 0;
 238         for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
 239                         n;
 240                         n--, k_tmp++, u_tmp++) {
 241                 k_tmp->len = u_tmp->len;
 242
 243                 total += k_tmp->len;
 244                 /* Check total length of transfers.  Also check each
 245                  * transfer length to avoid arithmetic overflow.
 246                  */
 247                 if (total > bufsiz || k_tmp->len > bufsiz) {
 248                         status = -EMSGSIZE;
 249                         goto done;
 250                 }
 251
 252                 if (u_tmp->rx_buf) {
 253                         k_tmp->rx_buf = buf;
 254                         if (!access_ok(VERIFY_WRITE, (u8 __user *)
 255                                                 (uintptr_t) u_tmp->rx_buf,
 256                                                 u_tmp->len))
 257                                 goto done;
 258                 }
 259                 if (u_tmp->tx_buf) {
 260                         k_tmp->tx_buf = buf;
 261                         if (copy_from_user(buf, (const u8 __user *)
 262                                                 (uintptr_t) u_tmp->tx_buf,
 263                                         u_tmp->len))
 264                                 goto done;
 265                 }
 266                 buf += k_tmp->len;
 267
 268                 k_tmp->cs_change = !!u_tmp->cs_change;
 269                 k_tmp->bits_per_word = u_tmp->bits_per_word;
 270                 k_tmp->delay_usecs = u_tmp->delay_usecs;
 271                 k_tmp->speed_hz = u_tmp->speed_hz;
 272 #ifdef VERBOSE
 273                 dev_dbg(&spidev->spi->dev,
 274                         "  xfer len %zd %s%s%s%dbits %u usec %uHz\n",
 275                         u_tmp->len,
 276                         u_tmp->rx_buf ? "rx " : "",
 277                         u_tmp->tx_buf ? "tx " : "",
 278                         u_tmp->cs_change ? "cs " : "",
 279                         u_tmp->bits_per_word ? : spidev->spi->bits_per_word,
 280                         u_tmp->delay_usecs,
 281                         u_tmp->speed_hz ? : spidev->spi->max_speed_hz);
 282 #endif
 283                 spi_message_add_tail(k_tmp, &msg);
 284         }
 285
 286         status = spidev_sync(spidev, &msg);
 287         if (status < 0)
 288                 goto done;
 289
 290         /* copy any rx data out of bounce buffer */
 291         buf = spidev->buffer;
 292         for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
 293                 if (u_tmp->rx_buf) {
 294                         if (__copy_to_user((u8 __user *)
 295                                         (uintptr_t) u_tmp->rx_buf, buf,
 296                                         u_tmp->len)) {
 297                                 status = -EFAULT;
 298                                 goto done;
 299                         }
 300                 }
 301                 buf += u_tmp->len;
 302         }
 303         status = total;
 304
 305 done:
 306         kfree(k_xfers);
 307         return status;
 308 }
 309
 310 static long
 311 spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 312 {
 313         int                     err = 0;
 314         int                     retval = 0;
 315         struct spidev_data      *spidev;
 316         struct spi_device       *spi;
 317         u32                     tmp;
 318         unsigned                n_ioc;
 319         struct spi_ioc_transfer *ioc;
 320
 321         /* Check type and command number */
 322         if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)
 323                 return -ENOTTY;
 324
 325         /* Check access direction once here; don't repeat below.
 326          * IOC_DIR is from the user perspective, while access_ok is
 327          * from the kernel perspective; so they look reversed.
 328          */
 329         if (_IOC_DIR(cmd) & _IOC_READ)
 330                 err = !access_ok(VERIFY_WRITE,
 331                                 (void __user *)arg, _IOC_SIZE(cmd));
 332         if (err == 0 && _IOC_DIR(cmd) & _IOC_WRITE)
 333                 err = !access_ok(VERIFY_READ,
 334                                 (void __user *)arg, _IOC_SIZE(cmd));
 335         if (err)
 336                 return -EFAULT;
 337
 338         /* guard against device removal before, or while,
 339          * we issue this ioctl.
 340          */
 341         spidev = filp->private_data;
 342         spin_lock_irq(&spidev->spi_lock);
 343         spi = spi_dev_get(spidev->spi);
 344         spin_unlock_irq(&spidev->spi_lock);
 345
 346         if (spi == NULL)
 347                 return -ESHUTDOWN;
 348
 349         /* use the buffer lock here for triple duty:
 350          *  - prevent I/O (from us) so calling spi_setup() is safe;
 351          *  - prevent concurrent SPI_IOC_WR_* from morphing
 352          *    data fields while SPI_IOC_RD_* reads them;
 353          *  - SPI_IOC_MESSAGE needs the buffer locked "normally".
 354          */
 355         mutex_lock(&spidev->buf_lock);
 356
 357         switch (cmd) {
 358         /* read requests */
 359         case SPI_IOC_RD_MODE:
 360                 retval = __put_user(spi->mode & SPI_MODE_MASK,
 361                                         (__u8 __user *)arg);
 362                 break;
 363         case SPI_IOC_RD_LSB_FIRST:
 364                 retval = __put_user((spi->mode & SPI_LSB_FIRST) ?  1 : 0,
 365                                         (__u8 __user *)arg);
 366                 break;
 367         case SPI_IOC_RD_BITS_PER_WORD:
 368                 retval = __put_user(spi->bits_per_word, (__u8 __user *)arg);
 369                 break;
 370         case SPI_IOC_RD_MAX_SPEED_HZ:
 371                 retval = __put_user(spi->max_speed_hz, (__u32 __user *)arg);
 372                 break;
 373
 374         /* write requests */
 375         case SPI_IOC_WR_MODE:
 376                 retval = __get_user(tmp, (u8 __user *)arg);
 377                 if (retval == 0) {
 378                         u8      save = spi->mode;
 379
 380                         if (tmp & ~SPI_MODE_MASK) {
 381                                 retval = -EINVAL;
 382                                 break;
 383                         }
 384
 385                         tmp |= spi->mode & ~SPI_MODE_MASK;
 386                         spi->mode = (u8)tmp;
 387                         retval = spi_setup(spi);
 388                         if (retval < 0)
 389                                 spi->mode = save;
 390                         else
 391                                 dev_dbg(&spi->dev, "spi mode %02x\n", tmp);
 392                 }
 393                 break;
 394         case SPI_IOC_WR_LSB_FIRST:
 395                 retval = __get_user(tmp, (__u8 __user *)arg);
 396                 if (retval == 0) {
 397                         u8      save = spi->mode;
 398
 399                         if (tmp)
 400                                 spi->mode |= SPI_LSB_FIRST;
 401                         else
 402                                 spi->mode &= ~SPI_LSB_FIRST;
 403                         retval = spi_setup(spi);
 404                         if (retval < 0)
 405                                 spi->mode = save;
 406                         else
 407                                 dev_dbg(&spi->dev, "%csb first\n",
 408                                                 tmp ? 'l' : 'm');
 409                 }
 410                 break;
 411         case SPI_IOC_WR_BITS_PER_WORD:
 412                 retval = __get_user(tmp, (__u8 __user *)arg);
 413                 if (retval == 0) {
 414                         u8      save = spi->bits_per_word;
 415
 416                         spi->bits_per_word = tmp;
 417                         retval = spi_setup(spi);
 418                         if (retval < 0)
 419                                 spi->bits_per_word = save;
 420                         else
 421                                 dev_dbg(&spi->dev, "%d bits per word\n", tmp);
 422                 }
 423                 break;
 424         case SPI_IOC_WR_MAX_SPEED_HZ:
 425                 retval = __get_user(tmp, (__u32 __user *)arg);
 426                 if (retval == 0) {
 427                         u32     save = spi->max_speed_hz;
 428
 429                         spi->max_speed_hz = tmp;
 430                         retval = spi_setup(spi);
 431                         if (retval < 0)
 432                                 spi->max_speed_hz = save;
 433                         else
 434                                 dev_dbg(&spi->dev, "%d Hz (max)\n", tmp);
 435                 }
 436                 break;
 437
 438         default:
 439                 /* segmented and/or full-duplex I/O request */
 440                 if (_IOC_NR(cmd) != _IOC_NR(SPI_IOC_MESSAGE(0))
 441                                 || _IOC_DIR(cmd) != _IOC_WRITE) {
 442                         retval = -ENOTTY;
 443                         break;
 444                 }
 445
 446                 tmp = _IOC_SIZE(cmd);
 447                 if ((tmp % sizeof(struct spi_ioc_transfer)) != 0) {
 448                         retval = -EINVAL;
 449                         break;
 450                 }
 451                 n_ioc = tmp / sizeof(struct spi_ioc_transfer);
 452                 if (n_ioc == 0)
 453                         break;
 454
 455                 /* copy into scratch area */
 456                 ioc = kmalloc(tmp, GFP_KERNEL);
 457                 if (!ioc) {
 458                         retval = -ENOMEM;
 459                         break;
 460                 }
 461                 if (__copy_from_user(ioc, (void __user *)arg, tmp)) {
 462                         kfree(ioc);
 463                         retval = -EFAULT;
 464                         break;
 465                 }
 466
 467                 /* translate to spi_message, execute */
 468                 retval = spidev_message(spidev, ioc, n_ioc);
 469                 kfree(ioc);
 470                 break;
 471         }
 472
 473         mutex_unlock(&spidev->buf_lock);
 474         spi_dev_put(spi);
 475         return retval;
 476 }
 477
 478 #ifdef CONFIG_COMPAT
 479 static long
 480 spidev_compat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 481 {
 482         return spidev_ioctl(filp, cmd, (unsigned long)compat_ptr(arg));
 483 }
 484 #else
 485 #define spidev_compat_ioctl NULL
 486 #endif /* CONFIG_COMPAT */
 487
 488 static int spidev_open(struct inode *inode, struct file *filp)
 489 {
 490         struct spidev_data      *spidev;
 491         int                     status = -ENXIO;
 492
 493         mutex_lock(&device_list_lock);
 494
 495         list_for_each_entry(spidev, &device_list, device_entry) {
 496                 if (spidev->devt == inode->i_rdev) {
 497                         status = 0;
 498                         break;
 499                 }
 500         }
 501         if (status == 0) {
 502                 if (!spidev->buffer) {
 503                         spidev->buffer = kmalloc(bufsiz, GFP_KERNEL);
 504                         if (!spidev->buffer) {
 505                                 dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
 506                                 status = -ENOMEM;
 507                         }
 508                 }
 509                 if (status == 0) {
 510                         spidev->users++;
 511                         filp->private_data = spidev;
 512                         nonseekable_open(inode, filp);
 513                 }
 514         } else
 515                 pr_debug("spidev: nothing for minor %d\n", iminor(inode));
 516
 517         mutex_unlock(&device_list_lock);
 518         return status;
 519 }
 520
 521 static int spidev_release(struct inode *inode, struct file *filp)
 522 {
 523         struct spidev_data      *spidev;
 524         int                     status = 0;
 525
 526         mutex_lock(&device_list_lock);
 527         spidev = filp->private_data;
 528         filp->private_data = NULL;
 529
 530         /* last close? */
 531         spidev->users--;
 532         if (!spidev->users) {
 533                 int             dofree;
 534
 535                 kfree(spidev->buffer);
 536                 spidev->buffer = NULL;
 537
 538                 /* ... after we unbound from the underlying device? */
 539                 spin_lock_irq(&spidev->spi_lock);
 540                 dofree = (spidev->spi == NULL);
 541                 spin_unlock_irq(&spidev->spi_lock);
 542
 543                 if (dofree)
 544                         kfree(spidev);
 545         }
 546         mutex_unlock(&device_list_lock);
 547
 548         return status;
 549 }
 550
 551 static const struct file_operations spidev_fops = {
 552         .owner =        THIS_MODULE,
 553         /* REVISIT switch to aio primitives, so that userspace
 554          * gets more complete API coverage.  It'll simplify things
 555          * too, except for the locking.
 556          */
 557         .write =        spidev_write,
 558         .read =         spidev_read,
 559         .unlocked_ioctl = spidev_ioctl,
 560         .compat_ioctl = spidev_compat_ioctl,
 561         .open =         spidev_open,
 562         .release =      spidev_release,
 563         .llseek =       no_llseek,
 564 };
 565
 566 /*-------------------------------------------------------------------------*/
 567
 568 /* The main reason to have this class is to make mdev/udev create the
 569  * /dev/spidevB.C character device nodes exposing our userspace API.
 570  * It also simplifies memory management.
 571  */
 572
 573 static struct class *spidev_class;
 574
 575 /*-------------------------------------------------------------------------*/
 576
 577 static int __devinit spidev_probe(struct spi_device *spi)
 578 {
 579         struct spidev_data      *spidev;
 580         int                     status;
 581         unsigned long           minor;
 582
 583         /* Allocate driver data */
 584         spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
 585         if (!spidev)
 586                 return -ENOMEM;
 587
 588         /* Initialize the driver data */
 589         spidev->spi = spi;
 590         spin_lock_init(&spidev->spi_lock);
 591         mutex_init(&spidev->buf_lock);
 592
 593         INIT_LIST_HEAD(&spidev->device_entry);
 594
 595         /* If we can allocate a minor number, hook up this device.
 596          * Reusing minors is fine so long as udev or mdev is working.
 597          */
 598         mutex_lock(&device_list_lock);
 599         minor = find_first_zero_bit(minors, N_SPI_MINORS);
 600         if (minor < N_SPI_MINORS) {
 601                 struct device *dev;
 602
 603                 spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
 604                 dev = device_create(spidev_class, &spi->dev, spidev->devt,
 605                                     spidev, "spidev%d.%d",
 606                                     spi->master->bus_num, spi->chip_select);
 607                 status = IS_ERR(dev) ? PTR_ERR(dev) : 0;
 608         } else {
 609                 dev_dbg(&spi->dev, "no minor number available!\n");
 610                 status = -ENODEV;
 611         }
 612         if (status == 0) {
 613                 set_bit(minor, minors);
 614                 list_add(&spidev->device_entry, &device_list);
 615         }
 616         mutex_unlock(&device_list_lock);
 617
 618         if (status == 0)
 619                 spi_set_drvdata(spi, spidev);
 620         else
 621                 kfree(spidev);
 622
 623         return status;
 624 }
 625
 626 static int __devexit spidev_remove(struct spi_device *spi)
 627 {
 628         struct spidev_data      *spidev = spi_get_drvdata(spi);
 629
 630         /* make sure ops on existing fds can abort cleanly */
 631         spin_lock_irq(&spidev->spi_lock);
 632         spidev->spi = NULL;
 633         spi_set_drvdata(spi, NULL);
 634         spin_unlock_irq(&spidev->spi_lock);
 635
 636         /* prevent new opens */
 637         mutex_lock(&device_list_lock);
 638         list_del(&spidev->device_entry);
 639         device_destroy(spidev_class, spidev->devt);
 640         clear_bit(MINOR(spidev->devt), minors);
 641         if (spidev->users == 0)
 642                 kfree(spidev);
 643         mutex_unlock(&device_list_lock);
 644
 645         return 0;
 646 }
 647
 648 static struct spi_driver spidev_spi_driver = {
 649         .driver = {
 650                 .name =         "spidev",
 651                 .owner =        THIS_MODULE,
 652         },
 653         .probe =        spidev_probe,
 654         .remove =       __devexit_p(spidev_remove),
 655
 656         /* NOTE:  suspend/resume methods are not necessary here.
 657          * We don't do anything except pass the requests to/from
 658          * the underlying controller.  The refrigerator handles
 659          * most issues; the controller driver handles the rest.
 660          */
 661 };
 662
 663 /*-------------------------------------------------------------------------*/
 664
 665 static int __init spidev_init(void)
 666 {
 667         int status;
 668
 669         /* Claim our 256 reserved device numbers.  Then register a class
 670          * that will key udev/mdev to add/remove /dev nodes.  Last, register
 671          * the driver which manages those device numbers.
 672          */
 673         BUILD_BUG_ON(N_SPI_MINORS > 256);
 674         status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
 675         if (status < 0)
 676                 return status;
 677
 678         spidev_class = class_create(THIS_MODULE, "spidev");
 679         if (IS_ERR(spidev_class)) {
 680                 unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
 681                 return PTR_ERR(spidev_class);
 682         }
 683
 684         status = spi_register_driver(&spidev_spi_driver);
 685         if (status < 0) {
 686                 class_destroy(spidev_class);
 687                 unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
 688         }
 689         return status;
 690 }
 691 module_init(spidev_init);
 692
 693 static void __exit spidev_exit(void)
 694 {
 695         spi_unregister_driver(&spidev_spi_driver);
 696         class_destroy(spidev_class);
 697         unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
 698 }
 699 module_exit(spidev_exit);
 700
 701 MODULE_AUTHOR("Andrea Paterniani, <a.paterniani@swapp-eng.it>");
 702 MODULE_DESCRIPTION("User mode SPI device interface");
 703 MODULE_LICENSE("GPL");
 704 MODULE_ALIAS("spi:spidev");