dmaengine: at_xdmac: Use dma_pool_zalloc

[linux-2.6/btrfs-unstable.git] / drivers / base / dd.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);
        }
}