drivers/base/dd.c

   1 /*
   2  * drivers/base/dd.c - The core device/driver interactions.
   3  *
   4  * This file contains the (sometimes tricky) code that controls the
   5  * interactions between devices and drivers, which primarily includes
   6  * driver binding and unbinding.
   7  *
   8  * All of this code used to exist in drivers/base/bus.c, but was
   9  * relocated to here in the name of compartmentalization (since it wasn't
  10  * strictly code just for the 'struct bus_type'.
  11  *
  12  * Copyright (c) 2002-5 Patrick Mochel
  13  * Copyright (c) 2002-3 Open Source Development Labs
  14  * Copyright (c) 2007-2009 Greg Kroah-Hartman <gregkh@suse.de>
  15  * Copyright (c) 2007-2009 Novell Inc.
  16  *
  17  * This file is released under the GPLv2
  18  */
  19
  20 #include <linux/device.h>
  21 #include <linux/delay.h>
  22 #include <linux/module.h>
  23 #include <linux/kthread.h>
  24 #include <linux/wait.h>
  25 #include <linux/async.h>
  26 #include <linux/pm_runtime.h>
  27 #include <linux/pinctrl/devinfo.h>
  28
  29 #include "base.h"
  30 #include "power/power.h"
  31
  32 /*
  33  * Deferred Probe infrastructure.
  34  *
  35  * Sometimes driver probe order matters, but the kernel doesn't always have
  36  * dependency information which means some drivers will get probed before a
  37  * resource it depends on is available.  For example, an SDHCI driver may
  38  * first need a GPIO line from an i2c GPIO controller before it can be
  39  * initialized.  If a required resource is not available yet, a driver can
  40  * request probing to be deferred by returning -EPROBE_DEFER from its probe hook
  41  *
  42  * Deferred probe maintains two lists of devices, a pending list and an active
  43  * list.  A driver returning -EPROBE_DEFER causes the device to be added to the
  44  * pending list.  A successful driver probe will trigger moving all devices
  45  * from the pending to the active list so that the workqueue will eventually
  46  * retry them.
  47  *
  48  * The deferred_probe_mutex must be held any time the deferred_probe_*_list
  49  * of the (struct device*)->p->deferred_probe pointers are manipulated
  50  */
  51 static DEFINE_MUTEX(deferred_probe_mutex);
  52 static LIST_HEAD(deferred_probe_pending_list);
  53 static LIST_HEAD(deferred_probe_active_list);
  54 static struct workqueue_struct *deferred_wq;
  55 static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
  56
  57 /*
  58  * deferred_probe_work_func() - Retry probing devices in the active list.
  59  */
  60 static void deferred_probe_work_func(struct work_struct *work)
  61 {
  62         struct device *dev;
  63         struct device_private *private;
  64         /*
  65          * This block processes every device in the deferred 'active' list.
  66          * Each device is removed from the active list and passed to
  67          * bus_probe_device() to re-attempt the probe.  The loop continues
  68          * until every device in the active list is removed and retried.
  69          *
  70          * Note: Once the device is removed from the list and the mutex is
  71          * released, it is possible for the device get freed by another thread
  72          * and cause a illegal pointer dereference.  This code uses
  73          * get/put_device() to ensure the device structure cannot disappear
  74          * from under our feet.
  75          */
  76         mutex_lock(&deferred_probe_mutex);
  77         while (!list_empty(&deferred_probe_active_list)) {
  78                 private = list_first_entry(&deferred_probe_active_list,
  79                                         typeof(*dev->p), deferred_probe);
  80                 dev = private->device;
  81                 list_del_init(&private->deferred_probe);
  82
  83                 get_device(dev);
  84
  85                 /*
  86                  * Drop the mutex while probing each device; the probe path may
  87                  * manipulate the deferred list
  88                  */
  89                 mutex_unlock(&deferred_probe_mutex);
  90
  91                 /*
  92                  * Force the device to the end of the dpm_list since
  93                  * the PM code assumes that the order we add things to
  94                  * the list is a good order for suspend but deferred
  95                  * probe makes that very unsafe.
  96                  */
  97                 device_pm_lock();
  98                 device_pm_move_last(dev);
  99                 device_pm_unlock();
 100
 101                 dev_dbg(dev, "Retrying from deferred list\n");
 102                 bus_probe_device(dev);
 103
 104                 mutex_lock(&deferred_probe_mutex);
 105
 106                 put_device(dev);
 107         }
 108         mutex_unlock(&deferred_probe_mutex);
 109 }
 110 static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
 111
 112 static void driver_deferred_probe_add(struct device *dev)
 113 {
 114         mutex_lock(&deferred_probe_mutex);
 115         if (list_empty(&dev->p->deferred_probe)) {
 116                 dev_dbg(dev, "Added to deferred list\n");
 117                 list_add_tail(&dev->p->deferred_probe, &deferred_probe_pending_list);
 118         }
 119         mutex_unlock(&deferred_probe_mutex);
 120 }
 121
 122 void driver_deferred_probe_del(struct device *dev)
 123 {
 124         mutex_lock(&deferred_probe_mutex);
 125         if (!list_empty(&dev->p->deferred_probe)) {
 126                 dev_dbg(dev, "Removed from deferred list\n");
 127                 list_del_init(&dev->p->deferred_probe);
 128         }
 129         mutex_unlock(&deferred_probe_mutex);
 130 }
 131
 132 static bool driver_deferred_probe_enable = false;
 133 /**
 134  * driver_deferred_probe_trigger() - Kick off re-probing deferred devices
 135  *
 136  * This functions moves all devices from the pending list to the active
 137  * list and schedules the deferred probe workqueue to process them.  It
 138  * should be called anytime a driver is successfully bound to a device.
 139  *
 140  * Note, there is a race condition in multi-threaded probe. In the case where
 141  * more than one device is probing at the same time, it is possible for one
 142  * probe to complete successfully while another is about to defer. If the second
 143  * depends on the first, then it will get put on the pending list after the
 144  * trigger event has already occurred and will be stuck there.
 145  *
 146  * The atomic 'deferred_trigger_count' is used to determine if a successful
 147  * trigger has occurred in the midst of probing a driver. If the trigger count
 148  * changes in the midst of a probe, then deferred processing should be triggered
 149  * again.
 150  */
 151 static void driver_deferred_probe_trigger(void)
 152 {
 153         if (!driver_deferred_probe_enable)
 154                 return;
 155
 156         /*
 157          * A successful probe means that all the devices in the pending list
 158          * should be triggered to be reprobed.  Move all the deferred devices
 159          * into the active list so they can be retried by the workqueue
 160          */
 161         mutex_lock(&deferred_probe_mutex);
 162         atomic_inc(&deferred_trigger_count);
 163         list_splice_tail_init(&deferred_probe_pending_list,
 164                               &deferred_probe_active_list);
 165         mutex_unlock(&deferred_probe_mutex);
 166
 167         /*
 168          * Kick the re-probe thread.  It may already be scheduled, but it is
 169          * safe to kick it again.
 170          */
 171         queue_work(deferred_wq, &deferred_probe_work);
 172 }
 173
 174 /**
 175  * deferred_probe_initcall() - Enable probing of deferred devices
 176  *
 177  * We don't want to get in the way when the bulk of drivers are getting probed.
 178  * Instead, this initcall makes sure that deferred probing is delayed until
 179  * late_initcall time.
 180  */
 181 static int deferred_probe_initcall(void)
 182 {
 183         deferred_wq = create_singlethread_workqueue("deferwq");
 184         if (WARN_ON(!deferred_wq))
 185                 return -ENOMEM;
 186
 187         driver_deferred_probe_enable = true;
 188         driver_deferred_probe_trigger();
 189         /* Sort as many dependencies as possible before exiting initcalls */
 190         flush_workqueue(deferred_wq);
 191         return 0;
 192 }
 193 late_initcall(deferred_probe_initcall);
 194
 195 static void driver_bound(struct device *dev)
 196 {
 197         if (klist_node_attached(&dev->p->knode_driver)) {
 198                 printk(KERN_WARNING "%s: device %s already bound\n",
 199                         __func__, kobject_name(&dev->kobj));
 200                 return;
 201         }
 202
 203         pr_debug("driver: '%s': %s: bound to device '%s'\n", dev->driver->name,
 204                  __func__, dev_name(dev));
 205
 206         klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
 207
 208         /*
 209          * Make sure the device is no longer in one of the deferred lists and
 210          * kick off retrying all pending devices
 211          */
 212         driver_deferred_probe_del(dev);
 213         driver_deferred_probe_trigger();
 214
 215         if (dev->bus)
 216                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 217                                              BUS_NOTIFY_BOUND_DRIVER, dev);
 218 }
 219
 220 static int driver_sysfs_add(struct device *dev)
 221 {
 222         int ret;
 223
 224         if (dev->bus)
 225                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 226                                              BUS_NOTIFY_BIND_DRIVER, dev);
 227
 228         ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj,
 229                           kobject_name(&dev->kobj));
 230         if (ret == 0) {
 231                 ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj,
 232                                         "driver");
 233                 if (ret)
 234                         sysfs_remove_link(&dev->driver->p->kobj,
 235                                         kobject_name(&dev->kobj));
 236         }
 237         return ret;
 238 }
 239
 240 static void driver_sysfs_remove(struct device *dev)
 241 {
 242         struct device_driver *drv = dev->driver;
 243
 244         if (drv) {
 245                 sysfs_remove_link(&drv->p->kobj, kobject_name(&dev->kobj));
 246                 sysfs_remove_link(&dev->kobj, "driver");
 247         }
 248 }
 249
 250 /**
 251  * device_bind_driver - bind a driver to one device.
 252  * @dev: device.
 253  *
 254  * Allow manual attachment of a driver to a device.
 255  * Caller must have already set @dev->driver.
 256  *
 257  * Note that this does not modify the bus reference count
 258  * nor take the bus's rwsem. Please verify those are accounted
 259  * for before calling this. (It is ok to call with no other effort
 260  * from a driver's probe() method.)
 261  *
 262  * This function must be called with the device lock held.
 263  */
 264 int device_bind_driver(struct device *dev)
 265 {
 266         int ret;
 267
 268         ret = driver_sysfs_add(dev);
 269         if (!ret)
 270                 driver_bound(dev);
 271         return ret;
 272 }
 273 EXPORT_SYMBOL_GPL(device_bind_driver);
 274
 275 static atomic_t probe_count = ATOMIC_INIT(0);
 276 static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
 277
 278 static int really_probe(struct device *dev, struct device_driver *drv)
 279 {
 280         int ret = 0;
 281         int local_trigger_count = atomic_read(&deferred_trigger_count);
 282
 283         atomic_inc(&probe_count);
 284         pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
 285                  drv->bus->name, __func__, drv->name, dev_name(dev));
 286         WARN_ON(!list_empty(&dev->devres_head));
 287
 288         dev->driver = drv;
 289
 290         /* If using pinctrl, bind pins now before probing */
 291         ret = pinctrl_bind_pins(dev);
 292         if (ret)
 293                 goto probe_failed;
 294
 295         if (driver_sysfs_add(dev)) {
 296                 printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
 297                         __func__, dev_name(dev));
 298                 goto probe_failed;
 299         }
 300
 301         if (dev->pm_domain && dev->pm_domain->activate) {
 302                 ret = dev->pm_domain->activate(dev);
 303                 if (ret)
 304                         goto probe_failed;
 305         }
 306
 307         if (dev->bus->probe) {
 308                 ret = dev->bus->probe(dev);
 309                 if (ret)
 310                         goto probe_failed;
 311         } else if (drv->probe) {
 312                 ret = drv->probe(dev);
 313                 if (ret)
 314                         goto probe_failed;
 315         }
 316
 317         pinctrl_init_done(dev);
 318
 319         if (dev->pm_domain && dev->pm_domain->sync)
 320                 dev->pm_domain->sync(dev);
 321
 322         driver_bound(dev);
 323         ret = 1;
 324         pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
 325                  drv->bus->name, __func__, dev_name(dev), drv->name);
 326         goto done;
 327
 328 probe_failed:
 329         devres_release_all(dev);
 330         driver_sysfs_remove(dev);
 331         dev->driver = NULL;
 332         dev_set_drvdata(dev, NULL);
 333         if (dev->pm_domain && dev->pm_domain->dismiss)
 334                 dev->pm_domain->dismiss(dev);
 335
 336         switch (ret) {
 337         case -EPROBE_DEFER:
 338                 /* Driver requested deferred probing */
 339                 dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
 340                 driver_deferred_probe_add(dev);
 341                 /* Did a trigger occur while probing? Need to re-trigger if yes */
 342                 if (local_trigger_count != atomic_read(&deferred_trigger_count))
 343                         driver_deferred_probe_trigger();
 344                 break;
 345         case -ENODEV:
 346         case -ENXIO:
 347                 pr_debug("%s: probe of %s rejects match %d\n",
 348                          drv->name, dev_name(dev), ret);
 349                 break;
 350         default:
 351                 /* driver matched but the probe failed */
 352                 printk(KERN_WARNING
 353                        "%s: probe of %s failed with error %d\n",
 354                        drv->name, dev_name(dev), ret);
 355         }
 356         /*
 357          * Ignore errors returned by ->probe so that the next driver can try
 358          * its luck.
 359          */
 360         ret = 0;
 361 done:
 362         atomic_dec(&probe_count);
 363         wake_up(&probe_waitqueue);
 364         return ret;
 365 }
 366
 367 /**
 368  * driver_probe_done
 369  * Determine if the probe sequence is finished or not.
 370  *
 371  * Should somehow figure out how to use a semaphore, not an atomic variable...
 372  */
 373 int driver_probe_done(void)
 374 {
 375         pr_debug("%s: probe_count = %d\n", __func__,
 376                  atomic_read(&probe_count));
 377         if (atomic_read(&probe_count))
 378                 return -EBUSY;
 379         return 0;
 380 }
 381
 382 /**
 383  * wait_for_device_probe
 384  * Wait for device probing to be completed.
 385  */
 386 void wait_for_device_probe(void)
 387 {
 388         /* wait for the known devices to complete their probing */
 389         wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
 390         async_synchronize_full();
 391 }
 392 EXPORT_SYMBOL_GPL(wait_for_device_probe);
 393
 394 /**
 395  * driver_probe_device - attempt to bind device & driver together
 396  * @drv: driver to bind a device to
 397  * @dev: device to try to bind to the driver
 398  *
 399  * This function returns -ENODEV if the device is not registered,
 400  * 1 if the device is bound successfully and 0 otherwise.
 401  *
 402  * This function must be called with @dev lock held.  When called for a
 403  * USB interface, @dev->parent lock must be held as well.
 404  *
 405  * If the device has a parent, runtime-resume the parent before driver probing.
 406  */
 407 int driver_probe_device(struct device_driver *drv, struct device *dev)
 408 {
 409         int ret = 0;
 410
 411         if (!device_is_registered(dev))
 412                 return -ENODEV;
 413
 414         pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 415                  drv->bus->name, __func__, dev_name(dev), drv->name);
 416
 417         if (dev->parent)
 418                 pm_runtime_get_sync(dev->parent);
 419
 420         pm_runtime_barrier(dev);
 421         ret = really_probe(dev, drv);
 422         pm_request_idle(dev);
 423
 424         if (dev->parent)
 425                 pm_runtime_put(dev->parent);
 426
 427         return ret;
 428 }
 429
 430 bool driver_allows_async_probing(struct device_driver *drv)
 431 {
 432         switch (drv->probe_type) {
 433         case PROBE_PREFER_ASYNCHRONOUS:
 434                 return true;
 435
 436         case PROBE_FORCE_SYNCHRONOUS:
 437                 return false;
 438
 439         default:
 440                 if (module_requested_async_probing(drv->owner))
 441                         return true;
 442
 443                 return false;
 444         }
 445 }
 446
 447 struct device_attach_data {
 448         struct device *dev;
 449
 450         /*
 451          * Indicates whether we are are considering asynchronous probing or
 452          * not. Only initial binding after device or driver registration
 453          * (including deferral processing) may be done asynchronously, the
 454          * rest is always synchronous, as we expect it is being done by
 455          * request from userspace.
 456          */
 457         bool check_async;
 458
 459         /*
 460          * Indicates if we are binding synchronous or asynchronous drivers.
 461          * When asynchronous probing is enabled we'll execute 2 passes
 462          * over drivers: first pass doing synchronous probing and second
 463          * doing asynchronous probing (if synchronous did not succeed -
 464          * most likely because there was no driver requiring synchronous
 465          * probing - and we found asynchronous driver during first pass).
 466          * The 2 passes are done because we can't shoot asynchronous
 467          * probe for given device and driver from bus_for_each_drv() since
 468          * driver pointer is not guaranteed to stay valid once
 469          * bus_for_each_drv() iterates to the next driver on the bus.
 470          */
 471         bool want_async;
 472
 473         /*
 474          * We'll set have_async to 'true' if, while scanning for matching
 475          * driver, we'll encounter one that requests asynchronous probing.
 476          */
 477         bool have_async;
 478 };
 479
 480 static int __device_attach_driver(struct device_driver *drv, void *_data)
 481 {
 482         struct device_attach_data *data = _data;
 483         struct device *dev = data->dev;
 484         bool async_allowed;
 485
 486         /*
 487          * Check if device has already been claimed. This may
 488          * happen with driver loading, device discovery/registration,
 489          * and deferred probe processing happens all at once with
 490          * multiple threads.
 491          */
 492         if (dev->driver)
 493                 return -EBUSY;
 494
 495         if (!driver_match_device(drv, dev))
 496                 return 0;
 497
 498         async_allowed = driver_allows_async_probing(drv);
 499
 500         if (async_allowed)
 501                 data->have_async = true;
 502
 503         if (data->check_async && async_allowed != data->want_async)
 504                 return 0;
 505
 506         return driver_probe_device(drv, dev);
 507 }
 508
 509 static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
 510 {
 511         struct device *dev = _dev;
 512         struct device_attach_data data = {
 513                 .dev            = dev,
 514                 .check_async    = true,
 515                 .want_async     = true,
 516         };
 517
 518         device_lock(dev);
 519
 520         if (dev->parent)
 521                 pm_runtime_get_sync(dev->parent);
 522
 523         bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver);
 524         dev_dbg(dev, "async probe completed\n");
 525
 526         pm_request_idle(dev);
 527
 528         if (dev->parent)
 529                 pm_runtime_put(dev->parent);
 530
 531         device_unlock(dev);
 532
 533         put_device(dev);
 534 }
 535
 536 static int __device_attach(struct device *dev, bool allow_async)
 537 {
 538         int ret = 0;
 539
 540         device_lock(dev);
 541         if (dev->driver) {
 542                 if (klist_node_attached(&dev->p->knode_driver)) {
 543                         ret = 1;
 544                         goto out_unlock;
 545                 }
 546                 ret = device_bind_driver(dev);
 547                 if (ret == 0)
 548                         ret = 1;
 549                 else {
 550                         dev->driver = NULL;
 551                         ret = 0;
 552                 }
 553         } else {
 554                 struct device_attach_data data = {
 555                         .dev = dev,
 556                         .check_async = allow_async,
 557                         .want_async = false,
 558                 };
 559
 560                 if (dev->parent)
 561                         pm_runtime_get_sync(dev->parent);
 562
 563                 ret = bus_for_each_drv(dev->bus, NULL, &data,
 564                                         __device_attach_driver);
 565                 if (!ret && allow_async && data.have_async) {
 566                         /*
 567                          * If we could not find appropriate driver
 568                          * synchronously and we are allowed to do
 569                          * async probes and there are drivers that
 570                          * want to probe asynchronously, we'll
 571                          * try them.
 572                          */
 573                         dev_dbg(dev, "scheduling asynchronous probe\n");
 574                         get_device(dev);
 575                         async_schedule(__device_attach_async_helper, dev);
 576                 } else {
 577                         pm_request_idle(dev);
 578                 }
 579
 580                 if (dev->parent)
 581                         pm_runtime_put(dev->parent);
 582         }
 583 out_unlock:
 584         device_unlock(dev);
 585         return ret;
 586 }
 587
 588 /**
 589  * device_attach - try to attach device to a driver.
 590  * @dev: device.
 591  *
 592  * Walk the list of drivers that the bus has and call
 593  * driver_probe_device() for each pair. If a compatible
 594  * pair is found, break out and return.
 595  *
 596  * Returns 1 if the device was bound to a driver;
 597  * 0 if no matching driver was found;
 598  * -ENODEV if the device is not registered.
 599  *
 600  * When called for a USB interface, @dev->parent lock must be held.
 601  */
 602 int device_attach(struct device *dev)
 603 {
 604         return __device_attach(dev, false);
 605 }
 606 EXPORT_SYMBOL_GPL(device_attach);
 607
 608 void device_initial_probe(struct device *dev)
 609 {
 610         __device_attach(dev, true);
 611 }
 612
 613 static int __driver_attach(struct device *dev, void *data)
 614 {
 615         struct device_driver *drv = data;
 616
 617         /*
 618          * Lock device and try to bind to it. We drop the error
 619          * here and always return 0, because we need to keep trying
 620          * to bind to devices and some drivers will return an error
 621          * simply if it didn't support the device.
 622          *
 623          * driver_probe_device() will spit a warning if there
 624          * is an error.
 625          */
 626
 627         if (!driver_match_device(drv, dev))
 628                 return 0;
 629
 630         if (dev->parent)        /* Needed for USB */
 631                 device_lock(dev->parent);
 632         device_lock(dev);
 633         if (!dev->driver)
 634                 driver_probe_device(drv, dev);
 635         device_unlock(dev);
 636         if (dev->parent)
 637                 device_unlock(dev->parent);
 638
 639         return 0;
 640 }
 641
 642 /**
 643  * driver_attach - try to bind driver to devices.
 644  * @drv: driver.
 645  *
 646  * Walk the list of devices that the bus has on it and try to
 647  * match the driver with each one.  If driver_probe_device()
 648  * returns 0 and the @dev->driver is set, we've found a
 649  * compatible pair.
 650  */
 651 int driver_attach(struct device_driver *drv)
 652 {
 653         return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
 654 }
 655 EXPORT_SYMBOL_GPL(driver_attach);
 656
 657 /*
 658  * __device_release_driver() must be called with @dev lock held.
 659  * When called for a USB interface, @dev->parent lock must be held as well.
 660  */
 661 static void __device_release_driver(struct device *dev)
 662 {
 663         struct device_driver *drv;
 664
 665         drv = dev->driver;
 666         if (drv) {
 667                 if (driver_allows_async_probing(drv))
 668                         async_synchronize_full();
 669
 670                 pm_runtime_get_sync(dev);
 671
 672                 driver_sysfs_remove(dev);
 673
 674                 if (dev->bus)
 675                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 676                                                      BUS_NOTIFY_UNBIND_DRIVER,
 677                                                      dev);
 678
 679                 pm_runtime_put_sync(dev);
 680
 681                 if (dev->bus && dev->bus->remove)
 682                         dev->bus->remove(dev);
 683                 else if (drv->remove)
 684                         drv->remove(dev);
 685                 devres_release_all(dev);
 686                 dev->driver = NULL;
 687                 dev_set_drvdata(dev, NULL);
 688                 if (dev->pm_domain && dev->pm_domain->dismiss)
 689                         dev->pm_domain->dismiss(dev);
 690
 691                 klist_remove(&dev->p->knode_driver);
 692                 if (dev->bus)
 693                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 694                                                      BUS_NOTIFY_UNBOUND_DRIVER,
 695                                                      dev);
 696
 697         }
 698 }
 699
 700 /**
 701  * device_release_driver - manually detach device from driver.
 702  * @dev: device.
 703  *
 704  * Manually detach device from driver.
 705  * When called for a USB interface, @dev->parent lock must be held.
 706  */
 707 void device_release_driver(struct device *dev)
 708 {
 709         /*
 710          * If anyone calls device_release_driver() recursively from
 711          * within their ->remove callback for the same device, they
 712          * will deadlock right here.
 713          */
 714         device_lock(dev);
 715         __device_release_driver(dev);
 716         device_unlock(dev);
 717 }
 718 EXPORT_SYMBOL_GPL(device_release_driver);
 719
 720 /**
 721  * driver_detach - detach driver from all devices it controls.
 722  * @drv: driver.
 723  */
 724 void driver_detach(struct device_driver *drv)
 725 {
 726         struct device_private *dev_prv;
 727         struct device *dev;
 728
 729         for (;;) {
 730                 spin_lock(&drv->p->klist_devices.k_lock);
 731                 if (list_empty(&drv->p->klist_devices.k_list)) {
 732                         spin_unlock(&drv->p->klist_devices.k_lock);
 733                         break;
 734                 }
 735                 dev_prv = list_entry(drv->p->klist_devices.k_list.prev,
 736                                      struct device_private,
 737                                      knode_driver.n_node);
 738                 dev = dev_prv->device;
 739                 get_device(dev);
 740                 spin_unlock(&drv->p->klist_devices.k_lock);
 741
 742                 if (dev->parent)        /* Needed for USB */
 743                         device_lock(dev->parent);
 744                 device_lock(dev);
 745                 if (dev->driver == drv)
 746                         __device_release_driver(dev);
 747                 device_unlock(dev);
 748                 if (dev->parent)
 749                         device_unlock(dev->parent);
 750                 put_device(dev);
 751         }
 752 }