dd.c

// SPDX-License-Identifier: GPL-2.0
/*
 * 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.
 */

#include <linux/debugfs.h>
#include <linux/device.h>
#include <linux/delay.h>
#include <linux/dma-map-ops.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/async.h>
#include <linux/pm_domain.h>
#include <linux/pm_runtime.h>
#include <linux/pinctrl/devinfo.h>
#include <linux/slab.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);
static bool initcalls_done;

/* Save the async probe drivers' name from kernel cmdline */
#define ASYNC_DRV_NAMES_MAX_LEN	256
static char async_probe_drv_names[ASYNC_DRV_NAMES_MAX_LEN];
static bool async_probe_default;

/*
 * 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;

static void __device_set_deferred_probe_reason(const struct device *dev, char *reason)
{
	kfree(dev->p->deferred_probe_reason);
	dev->p->deferred_probe_reason = reason;
}

/*
 * 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);

		__device_set_deferred_probe_reason(dev, NULL);

		/*
		 * 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_move_to_tail(dev);

		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);

void driver_deferred_probe_add(struct device *dev)
{
	if (!dev_can_match(dev))
		return;

	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);
		__device_set_deferred_probe_reason(dev, NULL);
	}
	mutex_unlock(&deferred_probe_mutex);
}

static bool driver_deferred_probe_enable;
/**
 * 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.
 */
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.
	 */
	queue_work(system_dfl_wq, &deferred_probe_work);
}

/**
 * device_block_probing() - Block/defer 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();
}

/**
 * device_set_deferred_probe_reason() - Set defer probe reason message for device
 * @dev: the pointer to the struct device
 * @vaf: the pointer to va_format structure with message
 */
void device_set_deferred_probe_reason(const struct device *dev, struct va_format *vaf)
{
	const char *drv = dev_driver_string(dev);
	char *reason;

	mutex_lock(&deferred_probe_mutex);

	reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
	__device_set_deferred_probe_reason(dev, reason);

	mutex_unlock(&deferred_probe_mutex);
}

/*
 * deferred_devs_show() - Show the devices in the deferred probe pending list.
 */
static int deferred_devs_show(struct seq_file *s, void *data)
{
	struct device_private *curr;

	mutex_lock(&deferred_probe_mutex);

	list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
		seq_printf(s, "%s\t%s", dev_name(curr->device),
			   curr->deferred_probe_reason ?: "\n");

	mutex_unlock(&deferred_probe_mutex);

	return 0;
}
DEFINE_SHOW_ATTRIBUTE(deferred_devs);

static int driver_deferred_probe_timeout = CONFIG_DRIVER_DEFERRED_PROBE_TIMEOUT;

static int __init deferred_probe_timeout_setup(char *str)
{
	int timeout;

	if (!kstrtoint(str, 10, &timeout))
		driver_deferred_probe_timeout = timeout;
	return 1;
}
__setup("deferred_probe_timeout=", deferred_probe_timeout_setup);

/**
 * driver_deferred_probe_check_state() - Check deferred probe state
 * @dev: device to check
 *
 * Return:
 * * -ENODEV if initcalls have completed and modules are disabled.
 * * -ETIMEDOUT if the deferred probe timeout was set and has expired
 *   and modules are enabled.
 * * -EPROBE_DEFER in other cases.
 *
 * Drivers or subsystems can opt-in to calling this function instead of directly
 * returning -EPROBE_DEFER.
 */
int driver_deferred_probe_check_state(struct device *dev)
{
	if (!IS_ENABLED(CONFIG_MODULES) && initcalls_done) {
		dev_warn(dev, "ignoring dependency for device, assuming no driver\n");
		return -ENODEV;
	}

	if (!driver_deferred_probe_timeout && initcalls_done) {
		dev_warn(dev, "deferred probe timeout, ignoring dependency\n");
		return -ETIMEDOUT;
	}

	return -EPROBE_DEFER;
}
EXPORT_SYMBOL_GPL(driver_deferred_probe_check_state);

static void deferred_probe_timeout_work_func(struct work_struct *work)
{
	struct device_private *p;

	fw_devlink_drivers_done();

	driver_deferred_probe_timeout = 0;
	driver_deferred_probe_trigger();
	flush_work(&deferred_probe_work);

	mutex_lock(&deferred_probe_mutex);
	list_for_each_entry(p, &deferred_probe_pending_list, deferred_probe)
		dev_warn(p->device, "deferred probe pending: %s", p->deferred_probe_reason ?: "(reason unknown)\n");
	mutex_unlock(&deferred_probe_mutex);

	fw_devlink_probing_done();
}
static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);

void deferred_probe_extend_timeout(void)
{
	/*
	 * If the work hasn't been queued yet or if the work expired, don't
	 * start a new one.
	 */
	if (delayed_work_pending(&deferred_probe_timeout_work) &&
	    mod_delayed_work(system_percpu_wq, &deferred_probe_timeout_work,
			     secs_to_jiffies(driver_deferred_probe_timeout)))
		pr_debug("Extended deferred probe timeout by %d secs\n",
					driver_deferred_probe_timeout);
}

/**
 * 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)
{
	debugfs_create_file("devices_deferred", 0444, NULL, NULL,
			    &deferred_devs_fops);

	driver_deferred_probe_enable = true;
	driver_deferred_probe_trigger();
	/* Sort as many dependencies as possible before exiting initcalls */
	flush_work(&deferred_probe_work);
	initcalls_done = true;

	if (!IS_ENABLED(CONFIG_MODULES))
		fw_devlink_drivers_done();

	/*
	 * Trigger deferred probe again, this time we won't defer anything
	 * that is optional
	 */
	driver_deferred_probe_trigger();
	flush_work(&deferred_probe_work);

	if (driver_deferred_probe_timeout > 0) {
		schedule_delayed_work(&deferred_probe_timeout_work,
			driver_deferred_probe_timeout * HZ);
	}

	if (!IS_ENABLED(CONFIG_MODULES))
		fw_devlink_probing_done();

	return 0;
}
late_initcall(deferred_probe_initcall);

static void __exit deferred_probe_exit(void)
{
	debugfs_lookup_and_remove("devices_deferred", NULL);
}
__exitcall(deferred_probe_exit);

int __device_set_driver_override(struct device *dev, const char *s, size_t len)
{
	const char *new = NULL, *old;

	if (!s)
		return -EINVAL;

	/*
	 * The stored value will be used in sysfs show callback (sysfs_emit()),
	 * which has a length limit of PAGE_SIZE and adds a trailing newline.
	 * Thus we can store one character less to avoid truncation during sysfs
	 * show.
	 */
	if (len >= (PAGE_SIZE - 1))
		return -EINVAL;

	/*
	 * Compute the real length of the string in case userspace sends us a
	 * bunch of \0 characters like python likes to do.
	 */
	len = strlen(s);

	/* Handle trailing newline */
	if (len) {
		char *cp;

		cp = strnchr(s, len, '\n');
		if (cp)
			len = cp - s;
	}

	/*
	 * If empty string or "\n" passed, new remains NULL, clearing
	 * the driver_override.name.
	 */
	if (len) {
		new = kstrndup(s, len, GFP_KERNEL);
		if (!new)
			return -ENOMEM;
	}

	scoped_guard(spinlock, &dev->driver_override.lock) {
		old = dev->driver_override.name;
		dev->driver_override.name = new;
	}

	kfree(old);

	return 0;
}
EXPORT_SYMBOL_GPL(__device_set_driver_override);

/**
 * 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);
}
EXPORT_SYMBOL_GPL(device_is_bound);

static void driver_bound(struct device *dev)
{
	if (device_is_bound(dev)) {
		dev_warn(dev, "%s: device already bound\n", __func__);
		return;
	}

	dev_dbg(dev, "driver: '%s': %s: bound to device\n", dev->driver->name,
		__func__);

	klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices);
	device_links_driver_bound(dev);

	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();

	bus_notify(dev, BUS_NOTIFY_BOUND_DRIVER);
	kobject_uevent(&dev->kobj, KOBJ_BIND);
}

static ssize_t coredump_store(struct device *dev, struct device_attribute *attr,
			    const char *buf, size_t count)
{
	device_lock(dev);
	dev->driver->coredump(dev);
	device_unlock(dev);

	return count;
}
static DEVICE_ATTR_WO(coredump);

static int driver_sysfs_add(struct device *dev)
{
	int ret;

	bus_notify(dev, BUS_NOTIFY_BIND_DRIVER);

	ret = sysfs_create_link(&dev->driver->p->kobj, &dev->kobj,
				kobject_name(&dev->kobj));
	if (ret)
		goto fail;

	ret = sysfs_create_link(&dev->kobj, &dev->driver->p->kobj,
				"driver");
	if (ret)
		goto rm_dev;

	if (!IS_ENABLED(CONFIG_DEV_COREDUMP) || !dev->driver->coredump)
		return 0;

	ret = device_create_file(dev, &dev_attr_coredump);
	if (!ret)
		return 0;

	sysfs_remove_link(&dev->kobj, "driver");

rm_dev:
	sysfs_remove_link(&dev->driver->p->kobj,
			  kobject_name(&dev->kobj));

fail:
	return ret;
}

static void driver_sysfs_remove(struct device *dev)
{
	struct device_driver *drv = dev->driver;

	if (drv) {
		if (drv->coredump)
			device_remove_file(dev, &dev_attr_coredump);
		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.
 * Please verify that is 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.
 *
 * Callers should prefer to use device_driver_attach() instead.
 */
int device_bind_driver(struct device *dev)
{
	int ret;

	ret = driver_sysfs_add(dev);
	if (!ret) {
		device_links_force_bind(dev);
		driver_bound(dev);
	}
	else
		bus_notify(dev, BUS_NOTIFY_DRIVER_NOT_BOUND);
	return ret;
}
EXPORT_SYMBOL_GPL(device_bind_driver);

static atomic_t probe_count = ATOMIC_INIT(0);
static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);

static ssize_t state_synced_store(struct device *dev,
				  struct device_attribute *attr,
				  const char *buf, size_t count)
{
	int ret = 0;

	if (strcmp("1", buf))
		return -EINVAL;

	device_lock(dev);
	if (!dev_test_and_set_state_synced(dev))
		dev_sync_state(dev);
	else
		ret = -EINVAL;
	device_unlock(dev);

	return ret ? ret : count;
}

static ssize_t state_synced_show(struct device *dev,
				 struct device_attribute *attr, char *buf)
{
	bool val;

	device_lock(dev);
	val = dev_state_synced(dev);
	device_unlock(dev);

	return sysfs_emit(buf, "%u\n", val);
}
static DEVICE_ATTR_RW(state_synced);

static void device_unbind_cleanup(struct device *dev)
{
	if (dev->driver->p_cb.post_unbind_rust)
		dev->driver->p_cb.post_unbind_rust(dev);
	devres_release_all(dev);
	arch_teardown_dma_ops(dev);
	kfree(dev->dma_range_map);
	dev->dma_range_map = NULL;
	device_set_driver(dev, NULL);
	dev_set_drvdata(dev, NULL);
	dev_pm_domain_detach(dev, dev->power.detach_power_off);
	if (dev->pm_domain && dev->pm_domain->dismiss)
		dev->pm_domain->dismiss(dev);
	pm_runtime_reinit(dev);
	dev_pm_set_driver_flags(dev, 0);
}

static void device_remove(struct device *dev)
{
	device_remove_file(dev, &dev_attr_state_synced);
	device_remove_groups(dev, dev->driver->dev_groups);

	if (dev->bus && dev->bus->remove)
		dev->bus->remove(dev);
	else if (dev->driver->remove)
		dev->driver->remove(dev);
}

static int call_driver_probe(struct device *dev, const struct device_driver *drv)
{
	int ret = 0;

	if (dev->bus->probe)
		ret = dev->bus->probe(dev);
	else if (drv->probe)
		ret = drv->probe(dev);

	switch (ret) {
	case 0:
		break;
	case -EPROBE_DEFER:
		/* Driver requested deferred probing */
		dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
		break;
	case -ENODEV:
	case -ENXIO:
		dev_dbg(dev, "probe with driver %s rejects match %d\n",
			drv->name, ret);
		break;
	default:
		/* driver matched but the probe failed */
		dev_err(dev, "probe with driver %s failed with error %d\n",
			drv->name, ret);
		break;
	}

	return ret;
}

static int really_probe(struct device *dev, const struct device_driver *drv)
{
	bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) &&
			   !drv->suppress_bind_attrs;
	int ret, link_ret;

	if (defer_all_probes) {
		/*
		 * Value of defer_all_probes can be set only by
		 * device_block_probing() 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);
		return -EPROBE_DEFER;
	}

	link_ret = device_links_check_suppliers(dev);
	if (link_ret == -EPROBE_DEFER)
		return link_ret;

	dev_dbg(dev, "bus: '%s': %s: probing driver %s with device\n",
		drv->bus->name, __func__, drv->name);
	if (!list_empty(&dev->devres_head)) {
		dev_crit(dev, "Resources present before probing\n");
		ret = -EBUSY;
		goto done;
	}

re_probe:
	device_set_driver(dev, drv);

	/* If using pinctrl, bind pins now before probing */
	ret = pinctrl_bind_pins(dev);
	if (ret)
		goto pinctrl_bind_failed;

	if (dev->bus->dma_configure) {
		ret = dev->bus->dma_configure(dev);
		if (ret)
			goto pinctrl_bind_failed;
	}

	ret = driver_sysfs_add(dev);
	if (ret) {
		dev_err(dev, "%s: driver_sysfs_add failed\n", __func__);
		goto sysfs_failed;
	}

	if (dev->pm_domain && dev->pm_domain->activate) {
		ret = dev->pm_domain->activate(dev);
		if (ret)
			goto probe_failed;
	}

	ret = call_driver_probe(dev, drv);
	if (ret) {
		/*
		 * If fw_devlink_best_effort is active (denoted by -EAGAIN), the
		 * device might actually probe properly once some of its missing
		 * suppliers have probed. So, treat this as if the driver
		 * returned -EPROBE_DEFER.
		 */
		if (link_ret == -EAGAIN)
			ret = -EPROBE_DEFER;

		/*
		 * Return probe errors as positive values so that the callers
		 * can distinguish them from other errors.
		 */
		ret = -ret;
		goto probe_failed;
	}

	ret = device_add_groups(dev, drv->dev_groups);
	if (ret) {
		dev_err(dev, "device_add_groups() failed\n");
		goto dev_groups_failed;
	}

	if (dev_has_sync_state(dev)) {
		ret = device_create_file(dev, &dev_attr_state_synced);
		if (ret) {
			dev_err(dev, "state_synced sysfs add failed\n");
			goto dev_sysfs_state_synced_failed;
		}
	}

	if (test_remove) {
		test_remove = false;

		device_remove(dev);
		driver_sysfs_remove(dev);
		if (dev->bus && dev->bus->dma_cleanup)
			dev->bus->dma_cleanup(dev);
		device_unbind_cleanup(dev);

		goto re_probe;
	}

	pinctrl_init_done(dev);

	if (dev->pm_domain && dev->pm_domain->sync)
		dev->pm_domain->sync(dev);

	driver_bound(dev);
	dev_dbg(dev, "bus: '%s': %s: bound device to driver %s\n",
		drv->bus->name, __func__, drv->name);
	goto done;

dev_sysfs_state_synced_failed:
dev_groups_failed:
	device_remove(dev);
probe_failed:
	driver_sysfs_remove(dev);
sysfs_failed:
	bus_notify(dev, BUS_NOTIFY_DRIVER_NOT_BOUND);
	if (dev->bus && dev->bus->dma_cleanup)
		dev->bus->dma_cleanup(dev);
pinctrl_bind_failed:
	device_links_no_driver(dev);
	device_unbind_cleanup(dev);
done:
	return ret;
}

/*
 * For initcall_debug, show the driver probe time.
 */
static int really_probe_debug(struct device *dev, const struct device_driver *drv)
{
	ktime_t calltime, rettime;
	int ret;

	calltime = ktime_get();
	ret = really_probe(dev, drv);
	rettime = ktime_get();
	/*
	 * Don't change this to pr_debug() because that requires
	 * CONFIG_DYNAMIC_DEBUG and we want a simple 'initcall_debug' on the
	 * kernel commandline to print this all the time at the debug level.
	 */
	printk(KERN_DEBUG "probe of %s with driver %s returned %d after %lld usecs\n",
	       dev_name(dev), drv->name, ret, ktime_us_delta(rettime, calltime));
	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...
 */
bool __init driver_probe_done(void)
{
	int local_probe_count = atomic_read(&probe_count);

	pr_debug("%s: probe_count = %d\n", __func__, local_probe_count);
	return !local_probe_count;
}

/**
 * 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);

static int __driver_probe_device(const struct device_driver *drv, struct device *dev)
{
	int ret = 0;

	if (dev->p->dead || !device_is_registered(dev))
		return -ENODEV;
	if (dev->driver)
		return -EBUSY;

	/*
	 * In device_add(), the "struct device" gets linked into the subsystem's
	 * list of devices and broadcast to userspace (via uevent) before we're
	 * quite ready to probe. Those open pathways to driver probe before
	 * we've finished enough of device_add() to reliably support probe.
	 * Detect this and tell other pathways to try again later. device_add()
	 * itself will also try to probe immediately after setting
	 * "ready_to_probe".
	 */
	if (!dev_ready_to_probe(dev))
		return dev_err_probe(dev, -EPROBE_DEFER, "Device not ready to probe\n");

	/*
	 * Call dev_set_can_match() after calling dev_ready_to_probe(), so
	 * driver_deferred_probe_add() won't actually add the device to the
	 * deferred probe list when dev_ready_to_probe() returns false.
	 *
	 * When dev_ready_to_probe() returns false, it means that device_add()
	 * will do another probe() attempt for us.
	 */
	dev_set_can_match(dev);
	dev_dbg(dev, "bus: '%s': %s: matched device with driver %s\n",
		drv->bus->name, __func__, drv->name);

	pm_runtime_get_suppliers(dev);
	if (dev->parent)
		pm_runtime_get_sync(dev->parent);

	pm_runtime_barrier(dev);
	if (initcall_debug)
		ret = really_probe_debug(dev, drv);
	else
		ret = really_probe(dev, drv);
	pm_request_idle(dev);

	if (dev->parent)
		pm_runtime_put(dev->parent);

	pm_runtime_put_suppliers(dev);
	return ret;
}

/**
 * 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, -EBUSY if it
 * already has a driver, 0 if the device is bound successfully and a positive
 * (inverted) error code for failures from the ->probe method.
 *
 * 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.
 */
static int driver_probe_device(const struct device_driver *drv, struct device *dev)
{
	int trigger_count = atomic_read(&deferred_trigger_count);
	int ret;

	atomic_inc(&probe_count);
	ret = __driver_probe_device(drv, dev);
	if (ret == -EPROBE_DEFER || ret == EPROBE_DEFER) {
		driver_deferred_probe_add(dev);

		/*
		 * Did a trigger occur while probing? Need to re-trigger if yes
		 */
		if (trigger_count != atomic_read(&deferred_trigger_count) &&
		    !defer_all_probes)
			driver_deferred_probe_trigger();
	}
	atomic_dec(&probe_count);
	wake_up_all(&probe_waitqueue);
	return ret;
}

static inline bool cmdline_requested_async_probing(const char *drv_name)
{
	bool async_drv;

	async_drv = parse_option_str(async_probe_drv_names, drv_name);

	return (async_probe_default != async_drv);
}

/* The option format is "driver_async_probe=drv_name1,drv_name2,..." */
static int __init save_async_options(char *buf)
{
	if (strlen(buf) >= ASYNC_DRV_NAMES_MAX_LEN)
		pr_warn("Too long list of driver names for 'driver_async_probe'!\n");

	strscpy(async_probe_drv_names, buf, ASYNC_DRV_NAMES_MAX_LEN);
	async_probe_default = parse_option_str(async_probe_drv_names, "*");

	return 1;
}
__setup("driver_async_probe=", save_async_options);

static bool driver_allows_async_probing(const struct device_driver *drv)
{
	switch (drv->probe_type) {
	case PROBE_PREFER_ASYNCHRONOUS:
		return true;

	case PROBE_FORCE_SYNCHRONOUS:
		return false;

	default:
		if (cmdline_requested_async_probing(drv->name))
			return true;

		if (module_requested_async_probing(drv->owner))
			return true;

		return false;
	}
}

struct device_attach_data {
	struct device *dev;

	/*
	 * Indicates whether we 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;

	ret = driver_match_device(drv, dev);
	if (ret == 0) {
		/* no match */
		return 0;
	} else if (ret == -EPROBE_DEFER) {