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 atomic_t deferred_trigger_count = ATOMIC_INIT(0);
  55
  56 static ssize_t deferred_probe_show(struct device *dev,
  57                                    struct device_attribute *attr, char *buf)
  58 {
  59         bool value;
  60
  61         mutex_lock(&deferred_probe_mutex);
  62         value = !list_empty(&dev->p->deferred_probe);
  63         mutex_unlock(&deferred_probe_mutex);
  64
  65         return sprintf(buf, "%d\n", value);
  66 }
  67 DEVICE_ATTR_RO(deferred_probe);
  68
  69 /*
  70  * In some cases, like suspend to RAM or hibernation, It might be reasonable
  71  * to prohibit probing of devices as it could be unsafe.
  72  * Once defer_all_probes is true all drivers probes will be forcibly deferred.
  73  */
  74 static bool defer_all_probes;
  75
  76 /*
  77  * deferred_probe_work_func() - Retry probing devices in the active list.
  78  */
  79 static void deferred_probe_work_func(struct work_struct *work)
  80 {
  81         struct device *dev;
  82         struct device_private *private;
  83         /*
  84          * This block processes every device in the deferred 'active' list.
  85          * Each device is removed from the active list and passed to
  86          * bus_probe_device() to re-attempt the probe.  The loop continues
  87          * until every device in the active list is removed and retried.
  88          *
  89          * Note: Once the device is removed from the list and the mutex is
  90          * released, it is possible for the device get freed by another thread
  91          * and cause a illegal pointer dereference.  This code uses
  92          * get/put_device() to ensure the device structure cannot disappear
  93          * from under our feet.
  94          */
  95         mutex_lock(&deferred_probe_mutex);
  96         while (!list_empty(&deferred_probe_active_list)) {
  97                 private = list_first_entry(&deferred_probe_active_list,
  98                                         typeof(*dev->p), deferred_probe);
  99                 dev = private->device;
 100                 list_del_init(&private->deferred_probe);
 101
 102                 get_device(dev);
 103
 104                 /*
 105                  * Drop the mutex while probing each device; the probe path may
 106                  * manipulate the deferred list
 107                  */
 108                 mutex_unlock(&deferred_probe_mutex);
 109
 110                 /*
 111                  * Force the device to the end of the dpm_list since
 112                  * the PM code assumes that the order we add things to
 113                  * the list is a good order for suspend but deferred
 114                  * probe makes that very unsafe.
 115                  */
 116                 device_pm_lock();
 117                 device_pm_move_last(dev);
 118                 device_pm_unlock();
 119
 120                 dev_dbg(dev, "Retrying from deferred list\n");
 121                 bus_probe_device(dev);
 122
 123                 mutex_lock(&deferred_probe_mutex);
 124
 125                 put_device(dev);
 126         }
 127         mutex_unlock(&deferred_probe_mutex);
 128 }
 129 static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
 130
 131 static void driver_deferred_probe_add(struct device *dev)
 132 {
 133         mutex_lock(&deferred_probe_mutex);
 134         if (list_empty(&dev->p->deferred_probe)) {
 135                 dev_dbg(dev, "Added to deferred list\n");
 136                 list_add_tail(&dev->p->deferred_probe, &deferred_probe_pending_list);
 137         }
 138         mutex_unlock(&deferred_probe_mutex);
 139 }
 140
 141 void driver_deferred_probe_del(struct device *dev)
 142 {
 143         mutex_lock(&deferred_probe_mutex);
 144         if (!list_empty(&dev->p->deferred_probe)) {
 145                 dev_dbg(dev, "Removed from deferred list\n");
 146                 list_del_init(&dev->p->deferred_probe);
 147         }
 148         mutex_unlock(&deferred_probe_mutex);
 149 }
 150
 151 static bool driver_deferred_probe_enable = false;
 152 /**
 153  * driver_deferred_probe_trigger() - Kick off re-probing deferred devices
 154  *
 155  * This functions moves all devices from the pending list to the active
 156  * list and schedules the deferred probe workqueue to process them.  It
 157  * should be called anytime a driver is successfully bound to a device.
 158  *
 159  * Note, there is a race condition in multi-threaded probe. In the case where
 160  * more than one device is probing at the same time, it is possible for one
 161  * probe to complete successfully while another is about to defer. If the second
 162  * depends on the first, then it will get put on the pending list after the
 163  * trigger event has already occurred and will be stuck there.
 164  *
 165  * The atomic 'deferred_trigger_count' is used to determine if a successful
 166  * trigger has occurred in the midst of probing a driver. If the trigger count
 167  * changes in the midst of a probe, then deferred processing should be triggered
 168  * again.
 169  */
 170 static void driver_deferred_probe_trigger(void)
 171 {
 172         if (!driver_deferred_probe_enable)
 173                 return;
 174
 175         /*
 176          * A successful probe means that all the devices in the pending list
 177          * should be triggered to be reprobed.  Move all the deferred devices
 178          * into the active list so they can be retried by the workqueue
 179          */
 180         mutex_lock(&deferred_probe_mutex);
 181         atomic_inc(&deferred_trigger_count);
 182         list_splice_tail_init(&deferred_probe_pending_list,
 183                               &deferred_probe_active_list);
 184         mutex_unlock(&deferred_probe_mutex);
 185
 186         /*
 187          * Kick the re-probe thread.  It may already be scheduled, but it is
 188          * safe to kick it again.
 189          */
 190         schedule_work(&deferred_probe_work);
 191 }
 192
 193 /**
 194  * device_block_probing() - Block/defere device's probes
 195  *
 196  *      It will disable probing of devices and defer their probes instead.
 197  */
 198 void device_block_probing(void)
 199 {
 200         defer_all_probes = true;
 201         /* sync with probes to avoid races. */
 202         wait_for_device_probe();
 203 }
 204
 205 /**
 206  * device_unblock_probing() - Unblock/enable device's probes
 207  *
 208  *      It will restore normal behavior and trigger re-probing of deferred
 209  * devices.
 210  */
 211 void device_unblock_probing(void)
 212 {
 213         defer_all_probes = false;
 214         driver_deferred_probe_trigger();
 215 }
 216
 217 /**
 218  * deferred_probe_initcall() - Enable probing of deferred devices
 219  *
 220  * We don't want to get in the way when the bulk of drivers are getting probed.
 221  * Instead, this initcall makes sure that deferred probing is delayed until
 222  * late_initcall time.
 223  */
 224 static int deferred_probe_initcall(void)
 225 {
 226         driver_deferred_probe_enable = true;
 227         driver_deferred_probe_trigger();
 228         /* Sort as many dependencies as possible before exiting initcalls */
 229         flush_work(&deferred_probe_work);
 230         return 0;
 231 }
 232 late_initcall(deferred_probe_initcall);
 233
 234 /**
 235  * device_is_bound() - Check if device is bound to a driver
 236  * @dev: device to check
 237  *
 238  * Returns true if passed device has already finished probing successfully
 239  * against a driver.
 240  *
 241  * This function must be called with the device lock held.
 242  */
 243 bool device_is_bound(struct device *dev)
 244 {
 245         return dev->p && klist_node_attached(&dev->p->knode_driver);
 246 }
 247
 248 static void driver_bound(struct device *dev)
 249 {
 250         if (device_is_bound(dev)) {
 251                 printk(KERN_WARNING "%s: device %s already bound\n",
 252                         __func__, kobject_name(&dev->kobj));
 253                 return;
 254         }
 255
 256         pr_debug("driver: '%s': %s: bound to device '%s'\n", dev->driver->name,
 257                  __func__, dev_name(dev));
 258
 259         klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
 260         device_links_driver_bound(dev);
 261
 262         device_pm_check_callbacks(dev);
 263
 264         /*
 265          * Make sure the device is no longer in one of the deferred lists and
 266          * kick off retrying all pending devices
 267          */
 268         driver_deferred_probe_del(dev);
 269         driver_deferred_probe_trigger();
 270
 271         if (dev->bus)
 272                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 273                                              BUS_NOTIFY_BOUND_DRIVER, dev);
 274 }
 275
 276 static int driver_sysfs_add(struct device *dev)
 277 {
 278         int ret;
 279
 280         if (dev->bus)
 281                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 282                                              BUS_NOTIFY_BIND_DRIVER, dev);
 283
 284         ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj,
 285                           kobject_name(&dev->kobj));
 286         if (ret == 0) {
 287                 ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj,
 288                                         "driver");
 289                 if (ret)
 290                         sysfs_remove_link(&dev->driver->p->kobj,
 291                                         kobject_name(&dev->kobj));
 292         }
 293         return ret;
 294 }
 295
 296 static void driver_sysfs_remove(struct device *dev)
 297 {
 298         struct device_driver *drv = dev->driver;
 299
 300         if (drv) {
 301                 sysfs_remove_link(&drv->p->kobj, kobject_name(&dev->kobj));
 302                 sysfs_remove_link(&dev->kobj, "driver");
 303         }
 304 }
 305
 306 /**
 307  * device_bind_driver - bind a driver to one device.
 308  * @dev: device.
 309  *
 310  * Allow manual attachment of a driver to a device.
 311  * Caller must have already set @dev->driver.
 312  *
 313  * Note that this does not modify the bus reference count
 314  * nor take the bus's rwsem. Please verify those are accounted
 315  * for before calling this. (It is ok to call with no other effort
 316  * from a driver's probe() method.)
 317  *
 318  * This function must be called with the device lock held.
 319  */
 320 int device_bind_driver(struct device *dev)
 321 {
 322         int ret;
 323
 324         ret = driver_sysfs_add(dev);
 325         if (!ret)
 326                 driver_bound(dev);
 327         else if (dev->bus)
 328                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 329                                              BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
 330         return ret;
 331 }
 332 EXPORT_SYMBOL_GPL(device_bind_driver);
 333
 334 static atomic_t probe_count = ATOMIC_INIT(0);
 335 static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
 336
 337 static int really_probe(struct device *dev, struct device_driver *drv)
 338 {
 339         int ret = -EPROBE_DEFER;
 340         int local_trigger_count = atomic_read(&deferred_trigger_count);
 341         bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) &&
 342                            !drv->suppress_bind_attrs;
 343
 344         if (defer_all_probes) {
 345                 /*
 346                  * Value of defer_all_probes can be set only by
 347                  * device_defer_all_probes_enable() which, in turn, will call
 348                  * wait_for_device_probe() right after that to avoid any races.
 349                  */
 350                 dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
 351                 driver_deferred_probe_add(dev);
 352                 return ret;
 353         }
 354
 355         ret = device_links_check_suppliers(dev);
 356         if (ret)
 357                 return ret;
 358
 359         atomic_inc(&probe_count);
 360         pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
 361                  drv->bus->name, __func__, drv->name, dev_name(dev));
 362         WARN_ON(!list_empty(&dev->devres_head));
 363
 364 re_probe:
 365         dev->driver = drv;
 366
 367         /* If using pinctrl, bind pins now before probing */
 368         ret = pinctrl_bind_pins(dev);
 369         if (ret)
 370                 goto pinctrl_bind_failed;
 371
 372         if (driver_sysfs_add(dev)) {
 373                 printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
 374                         __func__, dev_name(dev));
 375                 goto probe_failed;
 376         }
 377
 378         if (dev->pm_domain && dev->pm_domain->activate) {
 379                 ret = dev->pm_domain->activate(dev);
 380                 if (ret)
 381                         goto probe_failed;
 382         }
 383
 384         /*
 385          * Ensure devices are listed in devices_kset in correct order
 386          * It's important to move Dev to the end of devices_kset before
 387          * calling .probe, because it could be recursive and parent Dev
 388          * should always go first
 389          */
 390         devices_kset_move_last(dev);
 391
 392         if (dev->bus->probe) {
 393                 ret = dev->bus->probe(dev);
 394                 if (ret)
 395                         goto probe_failed;
 396         } else if (drv->probe) {
 397                 ret = drv->probe(dev);
 398                 if (ret)
 399                         goto probe_failed;
 400         }
 401
 402         if (test_remove) {
 403                 test_remove = false;
 404
 405                 if (dev->bus->remove)
 406                         dev->bus->remove(dev);
 407                 else if (drv->remove)
 408                         drv->remove(dev);
 409
 410                 devres_release_all(dev);
 411                 driver_sysfs_remove(dev);
 412                 dev->driver = NULL;
 413                 dev_set_drvdata(dev, NULL);
 414                 if (dev->pm_domain && dev->pm_domain->dismiss)
 415                         dev->pm_domain->dismiss(dev);
 416                 pm_runtime_reinit(dev);
 417
 418                 goto re_probe;
 419         }
 420
 421         pinctrl_init_done(dev);
 422
 423         if (dev->pm_domain && dev->pm_domain->sync)
 424                 dev->pm_domain->sync(dev);
 425
 426         driver_bound(dev);
 427         ret = 1;
 428         pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
 429                  drv->bus->name, __func__, dev_name(dev), drv->name);
 430         goto done;
 431
 432 probe_failed:
 433         if (dev->bus)
 434                 blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 435                                              BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
 436 pinctrl_bind_failed:
 437         device_links_no_driver(dev);
 438         devres_release_all(dev);
 439         driver_sysfs_remove(dev);
 440         dev->driver = NULL;
 441         dev_set_drvdata(dev, NULL);
 442         if (dev->pm_domain && dev->pm_domain->dismiss)
 443                 dev->pm_domain->dismiss(dev);
 444         pm_runtime_reinit(dev);
 445
 446         switch (ret) {
 447         case -EPROBE_DEFER:
 448                 /* Driver requested deferred probing */
 449                 dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
 450                 driver_deferred_probe_add(dev);
 451                 /* Did a trigger occur while probing? Need to re-trigger if yes */
 452                 if (local_trigger_count != atomic_read(&deferred_trigger_count))
 453                         driver_deferred_probe_trigger();
 454                 break;
 455         case -ENODEV:
 456         case -ENXIO:
 457                 pr_debug("%s: probe of %s rejects match %d\n",
 458                          drv->name, dev_name(dev), ret);
 459                 break;
 460         default:
 461                 /* driver matched but the probe failed */
 462                 printk(KERN_WARNING
 463                        "%s: probe of %s failed with error %d\n",
 464                        drv->name, dev_name(dev), ret);
 465         }
 466         /*
 467          * Ignore errors returned by ->probe so that the next driver can try
 468          * its luck.
 469          */
 470         ret = 0;
 471 done:
 472         atomic_dec(&probe_count);
 473         wake_up(&probe_waitqueue);
 474         return ret;
 475 }
 476
 477 /**
 478  * driver_probe_done
 479  * Determine if the probe sequence is finished or not.
 480  *
 481  * Should somehow figure out how to use a semaphore, not an atomic variable...
 482  */
 483 int driver_probe_done(void)
 484 {
 485         pr_debug("%s: probe_count = %d\n", __func__,
 486                  atomic_read(&probe_count));
 487         if (atomic_read(&probe_count))
 488                 return -EBUSY;
 489         return 0;
 490 }
 491
 492 /**
 493  * wait_for_device_probe
 494  * Wait for device probing to be completed.
 495  */
 496 void wait_for_device_probe(void)
 497 {
 498         /* wait for the deferred probe workqueue to finish */
 499         flush_work(&deferred_probe_work);
 500
 501         /* wait for the known devices to complete their probing */
 502         wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
 503         async_synchronize_full();
 504 }
 505 EXPORT_SYMBOL_GPL(wait_for_device_probe);
 506
 507 /**
 508  * driver_probe_device - attempt to bind device & driver together
 509  * @drv: driver to bind a device to
 510  * @dev: device to try to bind to the driver
 511  *
 512  * This function returns -ENODEV if the device is not registered,
 513  * 1 if the device is bound successfully and 0 otherwise.
 514  *
 515  * This function must be called with @dev lock held.  When called for a
 516  * USB interface, @dev->parent lock must be held as well.
 517  *
 518  * If the device has a parent, runtime-resume the parent before driver probing.
 519  */
 520 int driver_probe_device(struct device_driver *drv, struct device *dev)
 521 {
 522         int ret = 0;
 523
 524         if (!device_is_registered(dev))
 525                 return -ENODEV;
 526
 527         pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 528                  drv->bus->name, __func__, dev_name(dev), drv->name);
 529
 530         pm_runtime_get_suppliers(dev);
 531         if (dev->parent)
 532                 pm_runtime_get_sync(dev->parent);
 533
 534         pm_runtime_barrier(dev);
 535         ret = really_probe(dev, drv);
 536         pm_request_idle(dev);
 537
 538         if (dev->parent)
 539                 pm_runtime_put(dev->parent);
 540
 541         pm_runtime_put_suppliers(dev);
 542         return ret;
 543 }
 544
 545 bool driver_allows_async_probing(struct device_driver *drv)
 546 {
 547         switch (drv->probe_type) {
 548         case PROBE_PREFER_ASYNCHRONOUS:
 549                 return true;
 550
 551         case PROBE_FORCE_SYNCHRONOUS:
 552                 return false;
 553
 554         default:
 555                 if (module_requested_async_probing(drv->owner))
 556                         return true;
 557
 558                 return false;
 559         }
 560 }
 561
 562 struct device_attach_data {
 563         struct device *dev;
 564
 565         /*
 566          * Indicates whether we are are considering asynchronous probing or
 567          * not. Only initial binding after device or driver registration
 568          * (including deferral processing) may be done asynchronously, the
 569          * rest is always synchronous, as we expect it is being done by
 570          * request from userspace.
 571          */
 572         bool check_async;
 573
 574         /*
 575          * Indicates if we are binding synchronous or asynchronous drivers.
 576          * When asynchronous probing is enabled we'll execute 2 passes
 577          * over drivers: first pass doing synchronous probing and second
 578          * doing asynchronous probing (if synchronous did not succeed -
 579          * most likely because there was no driver requiring synchronous
 580          * probing - and we found asynchronous driver during first pass).
 581          * The 2 passes are done because we can't shoot asynchronous
 582          * probe for given device and driver from bus_for_each_drv() since
 583          * driver pointer is not guaranteed to stay valid once
 584          * bus_for_each_drv() iterates to the next driver on the bus.
 585          */
 586         bool want_async;
 587
 588         /*
 589          * We'll set have_async to 'true' if, while scanning for matching
 590          * driver, we'll encounter one that requests asynchronous probing.
 591          */
 592         bool have_async;
 593 };
 594
 595 static int __device_attach_driver(struct device_driver *drv, void *_data)
 596 {
 597         struct device_attach_data *data = _data;
 598         struct device *dev = data->dev;
 599         bool async_allowed;
 600         int ret;
 601
 602         /*
 603          * Check if device has already been claimed. This may
 604          * happen with driver loading, device discovery/registration,
 605          * and deferred probe processing happens all at once with
 606          * multiple threads.
 607          */
 608         if (dev->driver)
 609                 return -EBUSY;
 610
 611         ret = driver_match_device(drv, dev);
 612         if (ret == 0) {
 613                 /* no match */
 614                 return 0;
 615         } else if (ret == -EPROBE_DEFER) {
 616                 dev_dbg(dev, "Device match requests probe deferral\n");
 617                 driver_deferred_probe_add(dev);
 618         } else if (ret < 0) {
 619                 dev_dbg(dev, "Bus failed to match device: %d", ret);
 620                 return ret;
 621         } /* ret > 0 means positive match */
 622
 623         async_allowed = driver_allows_async_probing(drv);
 624
 625         if (async_allowed)
 626                 data->have_async = true;
 627
 628         if (data->check_async && async_allowed != data->want_async)
 629                 return 0;
 630
 631         return driver_probe_device(drv, dev);
 632 }
 633
 634 static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
 635 {
 636         struct device *dev = _dev;
 637         struct device_attach_data data = {
 638                 .dev            = dev,
 639                 .check_async    = true,
 640                 .want_async     = true,
 641         };
 642
 643         device_lock(dev);
 644
 645         if (dev->parent)
 646                 pm_runtime_get_sync(dev->parent);
 647
 648         bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver);
 649         dev_dbg(dev, "async probe completed\n");
 650
 651         pm_request_idle(dev);
 652
 653         if (dev->parent)
 654                 pm_runtime_put(dev->parent);
 655
 656         device_unlock(dev);
 657
 658         put_device(dev);
 659 }
 660
 661 static int __device_attach(struct device *dev, bool allow_async)
 662 {
 663         int ret = 0;
 664
 665         device_lock(dev);
 666         if (dev->driver) {
 667                 if (device_is_bound(dev)) {
 668                         ret = 1;
 669                         goto out_unlock;
 670                 }
 671                 ret = device_bind_driver(dev);
 672                 if (ret == 0)
 673                         ret = 1;
 674                 else {
 675                         dev->driver = NULL;
 676                         ret = 0;
 677                 }
 678         } else {
 679                 struct device_attach_data data = {
 680                         .dev = dev,
 681                         .check_async = allow_async,
 682                         .want_async = false,
 683                 };
 684
 685                 if (dev->parent)
 686                         pm_runtime_get_sync(dev->parent);
 687
 688                 ret = bus_for_each_drv(dev->bus, NULL, &data,
 689                                         __device_attach_driver);
 690                 if (!ret && allow_async && data.have_async) {
 691                         /*
 692                          * If we could not find appropriate driver
 693                          * synchronously and we are allowed to do
 694                          * async probes and there are drivers that
 695                          * want to probe asynchronously, we'll
 696                          * try them.
 697                          */
 698                         dev_dbg(dev, "scheduling asynchronous probe\n");
 699                         get_device(dev);
 700                         async_schedule(__device_attach_async_helper, dev);
 701                 } else {
 702                         pm_request_idle(dev);
 703                 }
 704
 705                 if (dev->parent)
 706                         pm_runtime_put(dev->parent);
 707         }
 708 out_unlock:
 709         device_unlock(dev);
 710         return ret;
 711 }
 712
 713 /**
 714  * device_attach - try to attach device to a driver.
 715  * @dev: device.
 716  *
 717  * Walk the list of drivers that the bus has and call
 718  * driver_probe_device() for each pair. If a compatible
 719  * pair is found, break out and return.
 720  *
 721  * Returns 1 if the device was bound to a driver;
 722  * 0 if no matching driver was found;
 723  * -ENODEV if the device is not registered.
 724  *
 725  * When called for a USB interface, @dev->parent lock must be held.
 726  */
 727 int device_attach(struct device *dev)
 728 {
 729         return __device_attach(dev, false);
 730 }
 731 EXPORT_SYMBOL_GPL(device_attach);
 732
 733 void device_initial_probe(struct device *dev)
 734 {
 735         __device_attach(dev, true);
 736 }
 737
 738 static int __driver_attach(struct device *dev, void *data)
 739 {
 740         struct device_driver *drv = data;
 741         int ret;
 742
 743         /*
 744          * Lock device and try to bind to it. We drop the error
 745          * here and always return 0, because we need to keep trying
 746          * to bind to devices and some drivers will return an error
 747          * simply if it didn't support the device.
 748          *
 749          * driver_probe_device() will spit a warning if there
 750          * is an error.
 751          */
 752
 753         ret = driver_match_device(drv, dev);
 754         if (ret == 0) {
 755                 /* no match */
 756                 return 0;
 757         } else if (ret == -EPROBE_DEFER) {
 758                 dev_dbg(dev, "Device match requests probe deferral\n");
 759                 driver_deferred_probe_add(dev);
 760         } else if (ret < 0) {
 761                 dev_dbg(dev, "Bus failed to match device: %d", ret);
 762                 return ret;
 763         } /* ret > 0 means positive match */
 764
 765         if (dev->parent)        /* Needed for USB */
 766                 device_lock(dev->parent);
 767         device_lock(dev);
 768         if (!dev->driver)
 769                 driver_probe_device(drv, dev);
 770         device_unlock(dev);
 771         if (dev->parent)
 772                 device_unlock(dev->parent);
 773
 774         return 0;
 775 }
 776
 777 /**
 778  * driver_attach - try to bind driver to devices.
 779  * @drv: driver.
 780  *
 781  * Walk the list of devices that the bus has on it and try to
 782  * match the driver with each one.  If driver_probe_device()
 783  * returns 0 and the @dev->driver is set, we've found a
 784  * compatible pair.
 785  */
 786 int driver_attach(struct device_driver *drv)
 787 {
 788         return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
 789 }
 790 EXPORT_SYMBOL_GPL(driver_attach);
 791
 792 /*
 793  * __device_release_driver() must be called with @dev lock held.
 794  * When called for a USB interface, @dev->parent lock must be held as well.
 795  */
 796 static void __device_release_driver(struct device *dev, struct device *parent)
 797 {
 798         struct device_driver *drv;
 799
 800         drv = dev->driver;
 801         if (drv) {
 802                 if (driver_allows_async_probing(drv))
 803                         async_synchronize_full();
 804
 805                 while (device_links_busy(dev)) {
 806                         device_unlock(dev);
 807                         if (parent)
 808                                 device_unlock(parent);
 809
 810                         device_links_unbind_consumers(dev);
 811                         if (parent)
 812                                 device_lock(parent);
 813
 814                         device_lock(dev);
 815                         /*
 816                          * A concurrent invocation of the same function might
 817                          * have released the driver successfully while this one
 818                          * was waiting, so check for that.
 819                          */
 820                         if (dev->driver != drv)
 821                                 return;
 822                 }
 823
 824                 pm_runtime_get_sync(dev);
 825                 pm_runtime_clean_up_links(dev);
 826
 827                 driver_sysfs_remove(dev);
 828
 829                 if (dev->bus)
 830                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 831                                                      BUS_NOTIFY_UNBIND_DRIVER,
 832                                                      dev);
 833
 834                 pm_runtime_put_sync(dev);
 835
 836                 if (dev->bus && dev->bus->remove)
 837                         dev->bus->remove(dev);
 838                 else if (drv->remove)
 839                         drv->remove(dev);
 840
 841                 device_links_driver_cleanup(dev);
 842                 devres_release_all(dev);
 843                 dev->driver = NULL;
 844                 dev_set_drvdata(dev, NULL);
 845                 if (dev->pm_domain && dev->pm_domain->dismiss)
 846                         dev->pm_domain->dismiss(dev);
 847                 pm_runtime_reinit(dev);
 848
 849                 klist_remove(&dev->p->knode_driver);
 850                 device_pm_check_callbacks(dev);
 851                 if (dev->bus)
 852                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 853                                                      BUS_NOTIFY_UNBOUND_DRIVER,
 854                                                      dev);
 855         }
 856 }
 857
 858 void device_release_driver_internal(struct device *dev,
 859                                     struct device_driver *drv,
 860                                     struct device *parent)
 861 {
 862         if (parent)
 863                 device_lock(parent);
 864
 865         device_lock(dev);
 866         if (!drv || drv == dev->driver)
 867                 __device_release_driver(dev, parent);
 868
 869         device_unlock(dev);
 870         if (parent)
 871                 device_unlock(parent);
 872 }
 873
 874 /**
 875  * device_release_driver - manually detach device from driver.
 876  * @dev: device.
 877  *
 878  * Manually detach device from driver.
 879  * When called for a USB interface, @dev->parent lock must be held.
 880  *
 881  * If this function is to be called with @dev->parent lock held, ensure that
 882  * the device's consumers are unbound in advance or that their locks can be
 883  * acquired under the @dev->parent lock.
 884  */
 885 void device_release_driver(struct device *dev)
 886 {
 887         /*
 888          * If anyone calls device_release_driver() recursively from
 889          * within their ->remove callback for the same device, they
 890          * will deadlock right here.
 891          */
 892         device_release_driver_internal(dev, NULL, NULL);
 893 }
 894 EXPORT_SYMBOL_GPL(device_release_driver);
 895
 896 /**
 897  * driver_detach - detach driver from all devices it controls.
 898  * @drv: driver.
 899  */
 900 void driver_detach(struct device_driver *drv)
 901 {
 902         struct device_private *dev_prv;
 903         struct device *dev;
 904
 905         for (;;) {
 906                 spin_lock(&drv->p->klist_devices.k_lock);
 907                 if (list_empty(&drv->p->klist_devices.k_list)) {
 908                         spin_unlock(&drv->p->klist_devices.k_lock);
 909                         break;
 910                 }
 911                 dev_prv = list_entry(drv->p->klist_devices.k_list.prev,
 912                                      struct device_private,
 913                                      knode_driver.n_node);
 914                 dev = dev_prv->device;
 915                 get_device(dev);
 916                 spin_unlock(&drv->p->klist_devices.k_lock);
 917                 device_release_driver_internal(dev, drv, dev->parent);
 918                 put_device(dev);
 919         }
 920 }