Version:  2.0.40 2.2.26 2.4.37 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4

Linux/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         /*
308          * Ensure devices are listed in devices_kset in correct order
309          * It's important to move Dev to the end of devices_kset before
310          * calling .probe, because it could be recursive and parent Dev
311          * should always go first
312          */
313         devices_kset_move_last(dev);
314 
315         if (dev->bus->probe) {
316                 ret = dev->bus->probe(dev);
317                 if (ret)
318                         goto probe_failed;
319         } else if (drv->probe) {
320                 ret = drv->probe(dev);
321                 if (ret)
322                         goto probe_failed;
323         }
324 
325         pinctrl_init_done(dev);
326 
327         if (dev->pm_domain && dev->pm_domain->sync)
328                 dev->pm_domain->sync(dev);
329 
330         driver_bound(dev);
331         ret = 1;
332         pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
333                  drv->bus->name, __func__, dev_name(dev), drv->name);
334         goto done;
335 
336 probe_failed:
337         devres_release_all(dev);
338         driver_sysfs_remove(dev);
339         dev->driver = NULL;
340         dev_set_drvdata(dev, NULL);
341         if (dev->pm_domain && dev->pm_domain->dismiss)
342                 dev->pm_domain->dismiss(dev);
343 
344         switch (ret) {
345         case -EPROBE_DEFER:
346                 /* Driver requested deferred probing */
347                 dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
348                 driver_deferred_probe_add(dev);
349                 /* Did a trigger occur while probing? Need to re-trigger if yes */
350                 if (local_trigger_count != atomic_read(&deferred_trigger_count))
351                         driver_deferred_probe_trigger();
352                 break;
353         case -ENODEV:
354         case -ENXIO:
355                 pr_debug("%s: probe of %s rejects match %d\n",
356                          drv->name, dev_name(dev), ret);
357                 break;
358         default:
359                 /* driver matched but the probe failed */
360                 printk(KERN_WARNING
361                        "%s: probe of %s failed with error %d\n",
362                        drv->name, dev_name(dev), ret);
363         }
364         /*
365          * Ignore errors returned by ->probe so that the next driver can try
366          * its luck.
367          */
368         ret = 0;
369 done:
370         atomic_dec(&probe_count);
371         wake_up(&probe_waitqueue);
372         return ret;
373 }
374 
375 /**
376  * driver_probe_done
377  * Determine if the probe sequence is finished or not.
378  *
379  * Should somehow figure out how to use a semaphore, not an atomic variable...
380  */
381 int driver_probe_done(void)
382 {
383         pr_debug("%s: probe_count = %d\n", __func__,
384                  atomic_read(&probe_count));
385         if (atomic_read(&probe_count))
386                 return -EBUSY;
387         return 0;
388 }
389 
390 /**
391  * wait_for_device_probe
392  * Wait for device probing to be completed.
393  */
394 void wait_for_device_probe(void)
395 {
396         /* wait for the known devices to complete their probing */
397         wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
398         async_synchronize_full();
399 }
400 EXPORT_SYMBOL_GPL(wait_for_device_probe);
401 
402 /**
403  * driver_probe_device - attempt to bind device & driver together
404  * @drv: driver to bind a device to
405  * @dev: device to try to bind to the driver
406  *
407  * This function returns -ENODEV if the device is not registered,
408  * 1 if the device is bound successfully and 0 otherwise.
409  *
410  * This function must be called with @dev lock held.  When called for a
411  * USB interface, @dev->parent lock must be held as well.
412  *
413  * If the device has a parent, runtime-resume the parent before driver probing.
414  */
415 int driver_probe_device(struct device_driver *drv, struct device *dev)
416 {
417         int ret = 0;
418 
419         if (!device_is_registered(dev))
420                 return -ENODEV;
421 
422         pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
423                  drv->bus->name, __func__, dev_name(dev), drv->name);
424 
425         if (dev->parent)
426                 pm_runtime_get_sync(dev->parent);
427 
428         pm_runtime_barrier(dev);
429         ret = really_probe(dev, drv);
430         pm_request_idle(dev);
431 
432         if (dev->parent)
433                 pm_runtime_put(dev->parent);
434 
435         return ret;
436 }
437 
438 bool driver_allows_async_probing(struct device_driver *drv)
439 {
440         switch (drv->probe_type) {
441         case PROBE_PREFER_ASYNCHRONOUS:
442                 return true;
443 
444         case PROBE_FORCE_SYNCHRONOUS:
445                 return false;
446 
447         default:
448                 if (module_requested_async_probing(drv->owner))
449                         return true;
450 
451                 return false;
452         }
453 }
454 
455 struct device_attach_data {
456         struct device *dev;
457 
458         /*
459          * Indicates whether we are are considering asynchronous probing or
460          * not. Only initial binding after device or driver registration
461          * (including deferral processing) may be done asynchronously, the
462          * rest is always synchronous, as we expect it is being done by
463          * request from userspace.
464          */
465         bool check_async;
466 
467         /*
468          * Indicates if we are binding synchronous or asynchronous drivers.
469          * When asynchronous probing is enabled we'll execute 2 passes
470          * over drivers: first pass doing synchronous probing and second
471          * doing asynchronous probing (if synchronous did not succeed -
472          * most likely because there was no driver requiring synchronous
473          * probing - and we found asynchronous driver during first pass).
474          * The 2 passes are done because we can't shoot asynchronous
475          * probe for given device and driver from bus_for_each_drv() since
476          * driver pointer is not guaranteed to stay valid once
477          * bus_for_each_drv() iterates to the next driver on the bus.
478          */
479         bool want_async;
480 
481         /*
482          * We'll set have_async to 'true' if, while scanning for matching
483          * driver, we'll encounter one that requests asynchronous probing.
484          */
485         bool have_async;
486 };
487 
488 static int __device_attach_driver(struct device_driver *drv, void *_data)
489 {
490         struct device_attach_data *data = _data;
491         struct device *dev = data->dev;
492         bool async_allowed;
493 
494         /*
495          * Check if device has already been claimed. This may
496          * happen with driver loading, device discovery/registration,
497          * and deferred probe processing happens all at once with
498          * multiple threads.
499          */
500         if (dev->driver)
501                 return -EBUSY;
502 
503         if (!driver_match_device(drv, dev))
504                 return 0;
505 
506         async_allowed = driver_allows_async_probing(drv);
507 
508         if (async_allowed)
509                 data->have_async = true;
510 
511         if (data->check_async && async_allowed != data->want_async)
512                 return 0;
513 
514         return driver_probe_device(drv, dev);
515 }
516 
517 static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
518 {
519         struct device *dev = _dev;
520         struct device_attach_data data = {
521                 .dev            = dev,
522                 .check_async    = true,
523                 .want_async     = true,
524         };
525 
526         device_lock(dev);
527 
528         if (dev->parent)
529                 pm_runtime_get_sync(dev->parent);
530 
531         bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver);
532         dev_dbg(dev, "async probe completed\n");
533 
534         pm_request_idle(dev);
535 
536         if (dev->parent)
537                 pm_runtime_put(dev->parent);
538 
539         device_unlock(dev);
540 
541         put_device(dev);
542 }
543 
544 static int __device_attach(struct device *dev, bool allow_async)
545 {
546         int ret = 0;
547 
548         device_lock(dev);
549         if (dev->driver) {
550                 if (klist_node_attached(&dev->p->knode_driver)) {
551                         ret = 1;
552                         goto out_unlock;
553                 }
554                 ret = device_bind_driver(dev);
555                 if (ret == 0)
556                         ret = 1;
557                 else {
558                         dev->driver = NULL;
559                         ret = 0;
560                 }
561         } else {
562                 struct device_attach_data data = {
563                         .dev = dev,
564                         .check_async = allow_async,
565                         .want_async = false,
566                 };
567 
568                 if (dev->parent)
569                         pm_runtime_get_sync(dev->parent);
570 
571                 ret = bus_for_each_drv(dev->bus, NULL, &data,
572                                         __device_attach_driver);
573                 if (!ret && allow_async && data.have_async) {
574                         /*
575                          * If we could not find appropriate driver
576                          * synchronously and we are allowed to do
577                          * async probes and there are drivers that
578                          * want to probe asynchronously, we'll
579                          * try them.
580                          */
581                         dev_dbg(dev, "scheduling asynchronous probe\n");
582                         get_device(dev);
583                         async_schedule(__device_attach_async_helper, dev);
584                 } else {
585                         pm_request_idle(dev);
586                 }
587 
588                 if (dev->parent)
589                         pm_runtime_put(dev->parent);
590         }
591 out_unlock:
592         device_unlock(dev);
593         return ret;
594 }
595 
596 /**
597  * device_attach - try to attach device to a driver.
598  * @dev: device.
599  *
600  * Walk the list of drivers that the bus has and call
601  * driver_probe_device() for each pair. If a compatible
602  * pair is found, break out and return.
603  *
604  * Returns 1 if the device was bound to a driver;
605  * 0 if no matching driver was found;
606  * -ENODEV if the device is not registered.
607  *
608  * When called for a USB interface, @dev->parent lock must be held.
609  */
610 int device_attach(struct device *dev)
611 {
612         return __device_attach(dev, false);
613 }
614 EXPORT_SYMBOL_GPL(device_attach);
615 
616 void device_initial_probe(struct device *dev)
617 {
618         __device_attach(dev, true);
619 }
620 
621 static int __driver_attach(struct device *dev, void *data)
622 {
623         struct device_driver *drv = data;
624 
625         /*
626          * Lock device and try to bind to it. We drop the error
627          * here and always return 0, because we need to keep trying
628          * to bind to devices and some drivers will return an error
629          * simply if it didn't support the device.
630          *
631          * driver_probe_device() will spit a warning if there
632          * is an error.
633          */
634 
635         if (!driver_match_device(drv, dev))
636                 return 0;
637 
638         if (dev->parent)        /* Needed for USB */
639                 device_lock(dev->parent);
640         device_lock(dev);
641         if (!dev->driver)
642                 driver_probe_device(drv, dev);
643         device_unlock(dev);
644         if (dev->parent)
645                 device_unlock(dev->parent);
646 
647         return 0;
648 }
649 
650 /**
651  * driver_attach - try to bind driver to devices.
652  * @drv: driver.
653  *
654  * Walk the list of devices that the bus has on it and try to
655  * match the driver with each one.  If driver_probe_device()
656  * returns 0 and the @dev->driver is set, we've found a
657  * compatible pair.
658  */
659 int driver_attach(struct device_driver *drv)
660 {
661         return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
662 }
663 EXPORT_SYMBOL_GPL(driver_attach);
664 
665 /*
666  * __device_release_driver() must be called with @dev lock held.
667  * When called for a USB interface, @dev->parent lock must be held as well.
668  */
669 static void __device_release_driver(struct device *dev)
670 {
671         struct device_driver *drv;
672 
673         drv = dev->driver;
674         if (drv) {
675                 if (driver_allows_async_probing(drv))
676                         async_synchronize_full();
677 
678                 pm_runtime_get_sync(dev);
679 
680                 driver_sysfs_remove(dev);
681 
682                 if (dev->bus)
683                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
684                                                      BUS_NOTIFY_UNBIND_DRIVER,
685                                                      dev);
686 
687                 pm_runtime_put_sync(dev);
688 
689                 if (dev->bus && dev->bus->remove)
690                         dev->bus->remove(dev);
691                 else if (drv->remove)
692                         drv->remove(dev);
693                 devres_release_all(dev);
694                 dev->driver = NULL;
695                 dev_set_drvdata(dev, NULL);
696                 if (dev->pm_domain && dev->pm_domain->dismiss)
697                         dev->pm_domain->dismiss(dev);
698 
699                 klist_remove(&dev->p->knode_driver);
700                 if (dev->bus)
701                         blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
702                                                      BUS_NOTIFY_UNBOUND_DRIVER,
703                                                      dev);
704 
705         }
706 }
707 
708 /**
709  * device_release_driver - manually detach device from driver.
710  * @dev: device.
711  *
712  * Manually detach device from driver.
713  * When called for a USB interface, @dev->parent lock must be held.
714  */
715 void device_release_driver(struct device *dev)
716 {
717         /*
718          * If anyone calls device_release_driver() recursively from
719          * within their ->remove callback for the same device, they
720          * will deadlock right here.
721          */
722         device_lock(dev);
723         __device_release_driver(dev);
724         device_unlock(dev);
725 }
726 EXPORT_SYMBOL_GPL(device_release_driver);
727 
728 /**
729  * driver_detach - detach driver from all devices it controls.
730  * @drv: driver.
731  */
732 void driver_detach(struct device_driver *drv)
733 {
734         struct device_private *dev_prv;
735         struct device *dev;
736 
737         for (;;) {
738                 spin_lock(&drv->p->klist_devices.k_lock);
739                 if (list_empty(&drv->p->klist_devices.k_list)) {
740                         spin_unlock(&drv->p->klist_devices.k_lock);
741                         break;
742                 }
743                 dev_prv = list_entry(drv->p->klist_devices.k_list.prev,
744                                      struct device_private,
745                                      knode_driver.n_node);
746                 dev = dev_prv->device;
747                 get_device(dev);
748                 spin_unlock(&drv->p->klist_devices.k_lock);
749 
750                 if (dev->parent)        /* Needed for USB */
751                         device_lock(dev->parent);
752                 device_lock(dev);
753                 if (dev->driver == drv)
754                         __device_release_driver(dev);
755                 device_unlock(dev);
756                 if (dev->parent)
757                         device_unlock(dev->parent);
758                 put_device(dev);
759         }
760 }
761 

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