linux/drivers/base/dd.c
Bhaktipriya Shridhar 2c507e464f device core: Remove deprecated create_singlethread_workqueue
The workqueue "deferred_wq" queues a single work item
&deferred_probe_work and hence doesn't require ordering.
It is involved in probing devices and is not being used on a memory
reclaim path. Hence, it has been converted to use system_wq.

System workqueues have been able to handle high level of concurrency
for a long time now and hence it's not required to have a singlethreaded
workqueue just to gain concurrency. Unlike a dedicated per-cpu workqueue
created with create_singlethread_workqueue(), system_wq allows multiple
work items to overlap executions even on the same CPU; however, a
per-cpu workqueue doesn't have any CPU locality or global ordering
guarantee unless the target CPU is explicitly specified and thus the
increase of local concurrency shouldn't make any difference.

The work item has been flushed in driver_probe_done() to ensure that
there are no pending tasks while disconnecting the driver.

Signed-off-by: Bhaktipriya Shridhar <bhaktipriya96@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2016-09-02 15:08:02 +02:00

867 lines
23 KiB
C

/*
* drivers/base/dd.c - The core device/driver interactions.
*
* This file contains the (sometimes tricky) code that controls the
* interactions between devices and drivers, which primarily includes
* driver binding and unbinding.
*
* All of this code used to exist in drivers/base/bus.c, but was
* relocated to here in the name of compartmentalization (since it wasn't
* strictly code just for the 'struct bus_type'.
*
* Copyright (c) 2002-5 Patrick Mochel
* Copyright (c) 2002-3 Open Source Development Labs
* Copyright (c) 2007-2009 Greg Kroah-Hartman <gregkh@suse.de>
* Copyright (c) 2007-2009 Novell Inc.
*
* This file is released under the GPLv2
*/
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/async.h>
#include <linux/pm_runtime.h>
#include <linux/pinctrl/devinfo.h>
#include "base.h"
#include "power/power.h"
/*
* Deferred Probe infrastructure.
*
* Sometimes driver probe order matters, but the kernel doesn't always have
* dependency information which means some drivers will get probed before a
* resource it depends on is available. For example, an SDHCI driver may
* first need a GPIO line from an i2c GPIO controller before it can be
* initialized. If a required resource is not available yet, a driver can
* request probing to be deferred by returning -EPROBE_DEFER from its probe hook
*
* Deferred probe maintains two lists of devices, a pending list and an active
* list. A driver returning -EPROBE_DEFER causes the device to be added to the
* pending list. A successful driver probe will trigger moving all devices
* from the pending to the active list so that the workqueue will eventually
* retry them.
*
* The deferred_probe_mutex must be held any time the deferred_probe_*_list
* of the (struct device*)->p->deferred_probe pointers are manipulated
*/
static DEFINE_MUTEX(deferred_probe_mutex);
static LIST_HEAD(deferred_probe_pending_list);
static LIST_HEAD(deferred_probe_active_list);
static atomic_t deferred_trigger_count = ATOMIC_INIT(0);
/*
* In some cases, like suspend to RAM or hibernation, It might be reasonable
* to prohibit probing of devices as it could be unsafe.
* Once defer_all_probes is true all drivers probes will be forcibly deferred.
*/
static bool defer_all_probes;
/*
* deferred_probe_work_func() - Retry probing devices in the active list.
*/
static void deferred_probe_work_func(struct work_struct *work)
{
struct device *dev;
struct device_private *private;
/*
* This block processes every device in the deferred 'active' list.
* Each device is removed from the active list and passed to
* bus_probe_device() to re-attempt the probe. The loop continues
* until every device in the active list is removed and retried.
*
* Note: Once the device is removed from the list and the mutex is
* released, it is possible for the device get freed by another thread
* and cause a illegal pointer dereference. This code uses
* get/put_device() to ensure the device structure cannot disappear
* from under our feet.
*/
mutex_lock(&deferred_probe_mutex);
while (!list_empty(&deferred_probe_active_list)) {
private = list_first_entry(&deferred_probe_active_list,
typeof(*dev->p), deferred_probe);
dev = private->device;
list_del_init(&private->deferred_probe);
get_device(dev);
/*
* Drop the mutex while probing each device; the probe path may
* manipulate the deferred list
*/
mutex_unlock(&deferred_probe_mutex);
/*
* Force the device to the end of the dpm_list since
* the PM code assumes that the order we add things to
* the list is a good order for suspend but deferred
* probe makes that very unsafe.
*/
device_pm_lock();
device_pm_move_last(dev);
device_pm_unlock();
dev_dbg(dev, "Retrying from deferred list\n");
bus_probe_device(dev);
mutex_lock(&deferred_probe_mutex);
put_device(dev);
}
mutex_unlock(&deferred_probe_mutex);
}
static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func);
static void driver_deferred_probe_add(struct device *dev)
{
mutex_lock(&deferred_probe_mutex);
if (list_empty(&dev->p->deferred_probe)) {
dev_dbg(dev, "Added to deferred list\n");
list_add_tail(&dev->p->deferred_probe, &deferred_probe_pending_list);
}
mutex_unlock(&deferred_probe_mutex);
}
void driver_deferred_probe_del(struct device *dev)
{
mutex_lock(&deferred_probe_mutex);
if (!list_empty(&dev->p->deferred_probe)) {
dev_dbg(dev, "Removed from deferred list\n");
list_del_init(&dev->p->deferred_probe);
}
mutex_unlock(&deferred_probe_mutex);
}
static bool driver_deferred_probe_enable = false;
/**
* driver_deferred_probe_trigger() - Kick off re-probing deferred devices
*
* This functions moves all devices from the pending list to the active
* list and schedules the deferred probe workqueue to process them. It
* should be called anytime a driver is successfully bound to a device.
*
* Note, there is a race condition in multi-threaded probe. In the case where
* more than one device is probing at the same time, it is possible for one
* probe to complete successfully while another is about to defer. If the second
* depends on the first, then it will get put on the pending list after the
* trigger event has already occurred and will be stuck there.
*
* The atomic 'deferred_trigger_count' is used to determine if a successful
* trigger has occurred in the midst of probing a driver. If the trigger count
* changes in the midst of a probe, then deferred processing should be triggered
* again.
*/
static void driver_deferred_probe_trigger(void)
{
if (!driver_deferred_probe_enable)
return;
/*
* A successful probe means that all the devices in the pending list
* should be triggered to be reprobed. Move all the deferred devices
* into the active list so they can be retried by the workqueue
*/
mutex_lock(&deferred_probe_mutex);
atomic_inc(&deferred_trigger_count);
list_splice_tail_init(&deferred_probe_pending_list,
&deferred_probe_active_list);
mutex_unlock(&deferred_probe_mutex);
/*
* Kick the re-probe thread. It may already be scheduled, but it is
* safe to kick it again.
*/
schedule_work(&deferred_probe_work);
}
/**
* device_block_probing() - Block/defere device's probes
*
* It will disable probing of devices and defer their probes instead.
*/
void device_block_probing(void)
{
defer_all_probes = true;
/* sync with probes to avoid races. */
wait_for_device_probe();
}
/**
* device_unblock_probing() - Unblock/enable device's probes
*
* It will restore normal behavior and trigger re-probing of deferred
* devices.
*/
void device_unblock_probing(void)
{
defer_all_probes = false;
driver_deferred_probe_trigger();
}
/**
* deferred_probe_initcall() - Enable probing of deferred devices
*
* We don't want to get in the way when the bulk of drivers are getting probed.
* Instead, this initcall makes sure that deferred probing is delayed until
* late_initcall time.
*/
static int deferred_probe_initcall(void)
{
driver_deferred_probe_enable = true;
driver_deferred_probe_trigger();
/* Sort as many dependencies as possible before exiting initcalls */
flush_work(&deferred_probe_work);
return 0;
}
late_initcall(deferred_probe_initcall);
/**
* device_is_bound() - Check if device is bound to a driver
* @dev: device to check
*
* Returns true if passed device has already finished probing successfully
* against a driver.
*
* This function must be called with the device lock held.
*/
bool device_is_bound(struct device *dev)
{
return dev->p && klist_node_attached(&dev->p->knode_driver);
}
static void driver_bound(struct device *dev)
{
if (device_is_bound(dev)) {
printk(KERN_WARNING "%s: device %s already bound\n",
__func__, kobject_name(&dev->kobj));
return;
}
pr_debug("driver: '%s': %s: bound to device '%s'\n", dev->driver->name,
__func__, dev_name(dev));
klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
device_pm_check_callbacks(dev);
/*
* Make sure the device is no longer in one of the deferred lists and
* kick off retrying all pending devices
*/
driver_deferred_probe_del(dev);
driver_deferred_probe_trigger();
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BOUND_DRIVER, dev);
}
static int driver_sysfs_add(struct device *dev)
{
int ret;
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_BIND_DRIVER, dev);
ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj,
kobject_name(&dev->kobj));
if (ret == 0) {
ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj,
"driver");
if (ret)
sysfs_remove_link(&dev->driver->p->kobj,
kobject_name(&dev->kobj));
}
return ret;
}
static void driver_sysfs_remove(struct device *dev)
{
struct device_driver *drv = dev->driver;
if (drv) {
sysfs_remove_link(&drv->p->kobj, kobject_name(&dev->kobj));
sysfs_remove_link(&dev->kobj, "driver");
}
}
/**
* device_bind_driver - bind a driver to one device.
* @dev: device.
*
* Allow manual attachment of a driver to a device.
* Caller must have already set @dev->driver.
*
* Note that this does not modify the bus reference count
* nor take the bus's rwsem. Please verify those are accounted
* for before calling this. (It is ok to call with no other effort
* from a driver's probe() method.)
*
* This function must be called with the device lock held.
*/
int device_bind_driver(struct device *dev)
{
int ret;
ret = driver_sysfs_add(dev);
if (!ret)
driver_bound(dev);
else if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
return ret;
}
EXPORT_SYMBOL_GPL(device_bind_driver);
static atomic_t probe_count = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
static int really_probe(struct device *dev, struct device_driver *drv)
{
int ret = -EPROBE_DEFER;
int local_trigger_count = atomic_read(&deferred_trigger_count);
bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE);
if (defer_all_probes) {
/*
* Value of defer_all_probes can be set only by
* device_defer_all_probes_enable() which, in turn, will call
* wait_for_device_probe() right after that to avoid any races.
*/
dev_dbg(dev, "Driver %s force probe deferral\n", drv->name);
driver_deferred_probe_add(dev);
return ret;
}
atomic_inc(&probe_count);
pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
drv->bus->name, __func__, drv->name, dev_name(dev));
WARN_ON(!list_empty(&dev->devres_head));
re_probe:
dev->driver = drv;
/* If using pinctrl, bind pins now before probing */
ret = pinctrl_bind_pins(dev);
if (ret)
goto pinctrl_bind_failed;
if (driver_sysfs_add(dev)) {
printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
__func__, dev_name(dev));
goto probe_failed;
}
if (dev->pm_domain && dev->pm_domain->activate) {
ret = dev->pm_domain->activate(dev);
if (ret)
goto probe_failed;
}
/*
* Ensure devices are listed in devices_kset in correct order
* It's important to move Dev to the end of devices_kset before
* calling .probe, because it could be recursive and parent Dev
* should always go first
*/
devices_kset_move_last(dev);
if (dev->bus->probe) {
ret = dev->bus->probe(dev);
if (ret)
goto probe_failed;
} else if (drv->probe) {
ret = drv->probe(dev);
if (ret)
goto probe_failed;
}
if (test_remove) {
test_remove = false;
if (dev->bus && dev->bus->remove)
dev->bus->remove(dev);
else if (drv->remove)
drv->remove(dev);
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
dev_set_drvdata(dev, NULL);
if (dev->pm_domain && dev->pm_domain->dismiss)
dev->pm_domain->dismiss(dev);
pm_runtime_reinit(dev);
goto re_probe;
}
pinctrl_init_done(dev);
if (dev->pm_domain && dev->pm_domain->sync)
dev->pm_domain->sync(dev);
driver_bound(dev);
ret = 1;
pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
goto done;
probe_failed:
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_DRIVER_NOT_BOUND, dev);
pinctrl_bind_failed:
devres_release_all(dev);
driver_sysfs_remove(dev);
dev->driver = NULL;
dev_set_drvdata(dev, NULL);
if (dev->pm_domain && dev->pm_domain->dismiss)
dev->pm_domain->dismiss(dev);
pm_runtime_reinit(dev);
switch (ret) {
case -EPROBE_DEFER:
/* Driver requested deferred probing */
dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
driver_deferred_probe_add(dev);
/* Did a trigger occur while probing? Need to re-trigger if yes */
if (local_trigger_count != atomic_read(&deferred_trigger_count))
driver_deferred_probe_trigger();
break;
case -ENODEV:
case -ENXIO:
pr_debug("%s: probe of %s rejects match %d\n",
drv->name, dev_name(dev), ret);
break;
default:
/* driver matched but the probe failed */
printk(KERN_WARNING
"%s: probe of %s failed with error %d\n",
drv->name, dev_name(dev), ret);
}
/*
* Ignore errors returned by ->probe so that the next driver can try
* its luck.
*/
ret = 0;
done:
atomic_dec(&probe_count);
wake_up(&probe_waitqueue);
return ret;
}
/**
* driver_probe_done
* Determine if the probe sequence is finished or not.
*
* Should somehow figure out how to use a semaphore, not an atomic variable...
*/
int driver_probe_done(void)
{
pr_debug("%s: probe_count = %d\n", __func__,
atomic_read(&probe_count));
if (atomic_read(&probe_count))
return -EBUSY;
return 0;
}
/**
* wait_for_device_probe
* Wait for device probing to be completed.
*/
void wait_for_device_probe(void)
{
/* wait for the deferred probe workqueue to finish */
flush_work(&deferred_probe_work);
/* wait for the known devices to complete their probing */
wait_event(probe_waitqueue, atomic_read(&probe_count) == 0);
async_synchronize_full();
}
EXPORT_SYMBOL_GPL(wait_for_device_probe);
/**
* driver_probe_device - attempt to bind device & driver together
* @drv: driver to bind a device to
* @dev: device to try to bind to the driver
*
* This function returns -ENODEV if the device is not registered,
* 1 if the device is bound successfully and 0 otherwise.
*
* This function must be called with @dev lock held. When called for a
* USB interface, @dev->parent lock must be held as well.
*
* If the device has a parent, runtime-resume the parent before driver probing.
*/
int driver_probe_device(struct device_driver *drv, struct device *dev)
{
int ret = 0;
if (!device_is_registered(dev))
return -ENODEV;
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);
if (dev->parent)
pm_runtime_get_sync(dev->parent);
pm_runtime_barrier(dev);
ret = really_probe(dev, drv);
pm_request_idle(dev);
if (dev->parent)
pm_runtime_put(dev->parent);
return ret;
}
bool driver_allows_async_probing(struct device_driver *drv)
{
switch (drv->probe_type) {
case PROBE_PREFER_ASYNCHRONOUS:
return true;
case PROBE_FORCE_SYNCHRONOUS:
return false;
default:
if (module_requested_async_probing(drv->owner))
return true;
return false;
}
}
struct device_attach_data {
struct device *dev;
/*
* Indicates whether we are are considering asynchronous probing or
* not. Only initial binding after device or driver registration
* (including deferral processing) may be done asynchronously, the
* rest is always synchronous, as we expect it is being done by
* request from userspace.
*/
bool check_async;
/*
* Indicates if we are binding synchronous or asynchronous drivers.
* When asynchronous probing is enabled we'll execute 2 passes
* over drivers: first pass doing synchronous probing and second
* doing asynchronous probing (if synchronous did not succeed -
* most likely because there was no driver requiring synchronous
* probing - and we found asynchronous driver during first pass).
* The 2 passes are done because we can't shoot asynchronous
* probe for given device and driver from bus_for_each_drv() since
* driver pointer is not guaranteed to stay valid once
* bus_for_each_drv() iterates to the next driver on the bus.
*/
bool want_async;
/*
* We'll set have_async to 'true' if, while scanning for matching
* driver, we'll encounter one that requests asynchronous probing.
*/
bool have_async;
};
static int __device_attach_driver(struct device_driver *drv, void *_data)
{
struct device_attach_data *data = _data;
struct device *dev = data->dev;
bool async_allowed;
int ret;
/*
* Check if device has already been claimed. This may
* happen with driver loading, device discovery/registration,
* and deferred probe processing happens all at once with
* multiple threads.
*/
if (dev->driver)
return -EBUSY;
ret = driver_match_device(drv, dev);
if (ret == 0) {
/* no match */
return 0;
} else if (ret == -EPROBE_DEFER) {
dev_dbg(dev, "Device match requests probe deferral\n");
driver_deferred_probe_add(dev);
} else if (ret < 0) {
dev_dbg(dev, "Bus failed to match device: %d", ret);
return ret;
} /* ret > 0 means positive match */
async_allowed = driver_allows_async_probing(drv);
if (async_allowed)
data->have_async = true;
if (data->check_async && async_allowed != data->want_async)
return 0;
return driver_probe_device(drv, dev);
}
static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
{
struct device *dev = _dev;
struct device_attach_data data = {
.dev = dev,
.check_async = true,
.want_async = true,
};
device_lock(dev);
if (dev->parent)
pm_runtime_get_sync(dev->parent);
bus_for_each_drv(dev->bus, NULL, &data, __device_attach_driver);
dev_dbg(dev, "async probe completed\n");
pm_request_idle(dev);
if (dev->parent)
pm_runtime_put(dev->parent);
device_unlock(dev);
put_device(dev);
}
static int __device_attach(struct device *dev, bool allow_async)
{
int ret = 0;
device_lock(dev);
if (dev->driver) {
if (device_is_bound(dev)) {
ret = 1;
goto out_unlock;
}
ret = device_bind_driver(dev);
if (ret == 0)
ret = 1;
else {
dev->driver = NULL;
ret = 0;
}
} else {
struct device_attach_data data = {
.dev = dev,
.check_async = allow_async,
.want_async = false,
};
if (dev->parent)
pm_runtime_get_sync(dev->parent);
ret = bus_for_each_drv(dev->bus, NULL, &data,
__device_attach_driver);
if (!ret && allow_async && data.have_async) {
/*
* If we could not find appropriate driver
* synchronously and we are allowed to do
* async probes and there are drivers that
* want to probe asynchronously, we'll
* try them.
*/
dev_dbg(dev, "scheduling asynchronous probe\n");
get_device(dev);
async_schedule(__device_attach_async_helper, dev);
} else {
pm_request_idle(dev);
}
if (dev->parent)
pm_runtime_put(dev->parent);
}
out_unlock:
device_unlock(dev);
return ret;
}
/**
* device_attach - try to attach device to a driver.
* @dev: device.
*
* Walk the list of drivers that the bus has and call
* driver_probe_device() for each pair. If a compatible
* pair is found, break out and return.
*
* Returns 1 if the device was bound to a driver;
* 0 if no matching driver was found;
* -ENODEV if the device is not registered.
*
* When called for a USB interface, @dev->parent lock must be held.
*/
int device_attach(struct device *dev)
{
return __device_attach(dev, false);
}
EXPORT_SYMBOL_GPL(device_attach);
void device_initial_probe(struct device *dev)
{
__device_attach(dev, true);
}
static int __driver_attach(struct device *dev, void *data)
{
struct device_driver *drv = data;
int ret;
/*
* Lock device and try to bind to it. We drop the error
* here and always return 0, because we need to keep trying
* to bind to devices and some drivers will return an error
* simply if it didn't support the device.
*
* driver_probe_device() will spit a warning if there
* is an error.
*/
ret = driver_match_device(drv, dev);
if (ret == 0) {
/* no match */
return 0;
} else if (ret == -EPROBE_DEFER) {
dev_dbg(dev, "Device match requests probe deferral\n");
driver_deferred_probe_add(dev);
} else if (ret < 0) {
dev_dbg(dev, "Bus failed to match device: %d", ret);
return ret;
} /* ret > 0 means positive match */
if (dev->parent) /* Needed for USB */
device_lock(dev->parent);
device_lock(dev);
if (!dev->driver)
driver_probe_device(drv, dev);
device_unlock(dev);
if (dev->parent)
device_unlock(dev->parent);
return 0;
}
/**
* driver_attach - try to bind driver to devices.
* @drv: driver.
*
* Walk the list of devices that the bus has on it and try to
* match the driver with each one. If driver_probe_device()
* returns 0 and the @dev->driver is set, we've found a
* compatible pair.
*/
int driver_attach(struct device_driver *drv)
{
return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}
EXPORT_SYMBOL_GPL(driver_attach);
/*
* __device_release_driver() must be called with @dev lock held.
* When called for a USB interface, @dev->parent lock must be held as well.
*/
static void __device_release_driver(struct device *dev)
{
struct device_driver *drv;
drv = dev->driver;
if (drv) {
if (driver_allows_async_probing(drv))
async_synchronize_full();
pm_runtime_get_sync(dev);
driver_sysfs_remove(dev);
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_UNBIND_DRIVER,
dev);
pm_runtime_put_sync(dev);
if (dev->bus && dev->bus->remove)
dev->bus->remove(dev);
else if (drv->remove)
drv->remove(dev);
devres_release_all(dev);
dev->driver = NULL;
dev_set_drvdata(dev, NULL);
if (dev->pm_domain && dev->pm_domain->dismiss)
dev->pm_domain->dismiss(dev);
pm_runtime_reinit(dev);
klist_remove(&dev->p->knode_driver);
device_pm_check_callbacks(dev);
if (dev->bus)
blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
BUS_NOTIFY_UNBOUND_DRIVER,
dev);
}
}
/**
* device_release_driver - manually detach device from driver.
* @dev: device.
*
* Manually detach device from driver.
* When called for a USB interface, @dev->parent lock must be held.
*/
void device_release_driver(struct device *dev)
{
/*
* If anyone calls device_release_driver() recursively from
* within their ->remove callback for the same device, they
* will deadlock right here.
*/
device_lock(dev);
__device_release_driver(dev);
device_unlock(dev);
}
EXPORT_SYMBOL_GPL(device_release_driver);
/**
* driver_detach - detach driver from all devices it controls.
* @drv: driver.
*/
void driver_detach(struct device_driver *drv)
{
struct device_private *dev_prv;
struct device *dev;
for (;;) {
spin_lock(&drv->p->klist_devices.k_lock);
if (list_empty(&drv->p->klist_devices.k_list)) {
spin_unlock(&drv->p->klist_devices.k_lock);
break;
}
dev_prv = list_entry(drv->p->klist_devices.k_list.prev,
struct device_private,
knode_driver.n_node);
dev = dev_prv->device;
get_device(dev);
spin_unlock(&drv->p->klist_devices.k_lock);
if (dev->parent) /* Needed for USB */
device_lock(dev->parent);
device_lock(dev);
if (dev->driver == drv)
__device_release_driver(dev);
device_unlock(dev);
if (dev->parent)
device_unlock(dev->parent);
put_device(dev);
}
}