text: // SPDX-License-Identifier: GPL-2.0-only
  /*
   * Backlight Lowlevel Control Abstraction
   *
   * Copyright (C) 2003,2004 Hewlett-Packard Company
   *
   */
  
  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/device.h>
  #include <linux/backlight.h>
  #include <linux/notifier.h>
  #include <linux/ctype.h>
  #include <linux/err.h>
  #include <linux/fb.h>
  #include <linux/slab.h>
  
  #ifdef CONFIG_PMAC_BACKLIGHT
  #include <asm/backlight.h>
  #endif
  
  /**
   * DOC: overview
   *
   * The backlight core supports implementing backlight drivers.
   *
   * A backlight driver registers a driver using
   * devm_backlight_device_register(). The properties of the backlight
   * driver such as type and max_brightness must be specified.
   * When the core detect changes in for example brightness or power state
   * the update_status() operation is called. The backlight driver shall
   * implement this operation and use it to adjust backlight.
   *
   * Several sysfs attributes are provided by the backlight core::
   *
   * - brightness         R/W, set the requested brightness level
   * - actual_brightness  RO, the brightness level used by the HW
   * - max_brightness     RO, the maximum  brightness level supported
   *
   * See Documentation/ABI/stable/sysfs-class-backlight for the full list.
   *
   * The backlight can be adjusted using the sysfs interface, and
   * the backlight driver may also support adjusting backlight using
   * a hot-key or some other platform or firmware specific way.
   *
   * The driver must implement the get_brightness() operation if
   * the HW do not support all the levels that can be specified in
   * brightness, thus providing user-space access to the actual level
   * via the actual_brightness attribute.
   *
   * When the backlight changes this is reported to user-space using
   * an uevent connected to the actual_brightness attribute.
   * When brightness is set by platform specific means, for example
   * a hot-key to adjust backlight, the driver must notify the backlight
   * core that brightness has changed using backlight_force_update().
   *
   * The backlight driver core receives notifications from fbdev and
   * if the event is FB_EVENT_BLANK and if the value of blank, from the
   * FBIOBLANK ioctrl, results in a change in the backlight state the
   * update_status() operation is called.
   */
  
  static struct list_head backlight_dev_list;
  static struct mutex backlight_dev_list_mutex;
  static struct blocking_notifier_head backlight_notifier;
  
  static const char *const backlight_types[] = {
  	[BACKLIGHT_RAW] = "raw",
  	[BACKLIGHT_PLATFORM] = "platform",
  	[BACKLIGHT_FIRMWARE] = "firmware",
  };
  
  static const char *const backlight_scale_types[] = {
  	[BACKLIGHT_SCALE_UNKNOWN]	= "unknown",
  	[BACKLIGHT_SCALE_LINEAR]	= "linear",
  	[BACKLIGHT_SCALE_NON_LINEAR]	= "non-linear",
  };
  
  #if defined(CONFIG_FB) || (defined(CONFIG_FB_MODULE) && \
  			   defined(CONFIG_BACKLIGHT_CLASS_DEVICE_MODULE))
  /*
   * fb_notifier_callback
   *
   * This callback gets called when something important happens inside a
   * framebuffer driver. The backlight core only cares about FB_BLANK_UNBLANK
   * which is reported to the driver using backlight_update_status()
   * as a state change.
   *
   * There may be several fbdev's connected to the backlight device,
   * in which case they are kept track of. A state change is only reported
   * if there is a change in backlight for the specified fbdev.
   */
  static int fb_notifier_callback(struct notifier_block *self,
  				unsigned long event, void *data)
  {
  	struct backlight_device *bd;
  	struct fb_event *evdata = data;
  	int node = evdata->info->node;
  	int fb_blank = 0;
  
  	/* If we aren't interested in this event, skip it immediately ... */
  	if (event != FB_EVENT_BLANK)
  		return 0;
  
  	bd = container_of(self, struct backlight_device, fb_notif);
  	mutex_lock(&bd->ops_lock);
  
  	if (!bd->ops)
  		goto out;
  	if (bd->ops->check_fb && !bd->ops->check_fb(bd, evdata->info))
  		goto out;
  
  	fb_blank = *(int *)evdata->data;
  	if (fb_blank == FB_BLANK_UNBLANK && !bd->fb_bl_on[node]) {
  		bd->fb_bl_on[node] = true;
  		if (!bd->use_count++) {
  			bd->props.state &= ~BL_CORE_FBBLANK;
  			bd->props.fb_blank = FB_BLANK_UNBLANK;
  			backlight_update_status(bd);
  		}
  	} else if (fb_blank != FB_BLANK_UNBLANK && bd->fb_bl_on[node]) {
  		bd->fb_bl_on[node] = false;
  		if (!(--bd->use_count)) {
  			bd->props.state |= BL_CORE_FBBLANK;
  			bd->props.fb_blank = fb_blank;
  			backlight_update_status(bd);
  		}
  	}
  out:
  	mutex_unlock(&bd->ops_lock);
  	return 0;
  }
  
  static int backlight_register_fb(struct backlight_device *bd)
  {
  	memset(&bd->fb_notif, 0, sizeof(bd->fb_notif));
  	bd->fb_notif.notifier_call = fb_notifier_callback;
  
  	return fb_register_client(&bd->fb_notif);
  }
  
  static void backlight_unregister_fb(struct backlight_device *bd)
  {
  	fb_unregister_client(&bd->fb_notif);
  }
  #else
  static inline int backlight_register_fb(struct backlight_device *bd)
  {
  	return 0;
  }
  
  static inline void backlight_unregister_fb(struct backlight_device *bd)
  {
  }
  #endif /* CONFIG_FB */
  
  static void backlight_generate_event(struct backlight_device *bd,
  				     enum backlight_update_reason reason)
  {
  	char *envp[2];
  
  	switch (reason) {
  	case BACKLIGHT_UPDATE_SYSFS:
  		envp[0] = "SOURCE=sysfs";
  		break;
  	case BACKLIGHT_UPDATE_HOTKEY:
  		envp[0] = "SOURCE=hotkey";
  		break;
  	default:
  		envp[0] = "SOURCE=unknown";
  		break;
  	}
  	envp[1] = NULL;
  	kobject_uevent_env(&bd->dev.kobj, KOBJ_CHANGE, envp);
  	sysfs_notify(&bd->dev.kobj, NULL, "actual_brightness");
  }
  
  static ssize_t bl_power_show(struct device *dev, struct device_attribute *attr,
  		char *buf)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	return sprintf(buf, "%d\n", bd->props.power);
  }
  
  static ssize_t bl_power_store(struct device *dev, struct device_attribute *attr,
  		const char *buf, size_t count)
  {
  	int rc;
  	struct backlight_device *bd = to_backlight_device(dev);
  	unsigned long power, old_power;
  
  	rc = kstrtoul(buf, 0, &power);
  	if (rc)
  		return rc;
  
  	rc = -ENXIO;
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops) {
  		pr_debug("set power to %lu\n", power);
  		if (bd->props.power != power) {
  			old_power = bd->props.power;
  			bd->props.power = power;
  			rc = backlight_update_status(bd);
  			if (rc)
  				bd->props.power = old_power;
  			else
  				rc = count;
  		} else {
  			rc = count;
  		}
  	}
  	mutex_unlock(&bd->ops_lock);
  
  	return rc;
  }
  static DEVICE_ATTR_RW(bl_power);
  
  static ssize_t brightness_show(struct device *dev,
  		struct device_attribute *attr, char *buf)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	return sprintf(buf, "%d\n", bd->props.brightness);
  }
  
  int backlight_device_set_brightness(struct backlight_device *bd,
  				    unsigned long brightness)
  {
  	int rc = -ENXIO;
  
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops) {
  		if (brightness > bd->props.max_brightness)
  			rc = -EINVAL;
  		else {
  			pr_debug("set brightness to %lu\n", brightness);
  			bd->props.brightness = brightness;
  			rc = backlight_update_status(bd);
  		}
  	}
  	mutex_unlock(&bd->ops_lock);
  
  	backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
  
  	return rc;
  }
  EXPORT_SYMBOL(backlight_device_set_brightness);
  
  static ssize_t brightness_store(struct device *dev,
  		struct device_attribute *attr, const char *buf, size_t count)
  {
  	int rc;
  	struct backlight_device *bd = to_backlight_device(dev);
  	unsigned long brightness;
  
  	rc = kstrtoul(buf, 0, &brightness);
  	if (rc)
  		return rc;
  
  	rc = backlight_device_set_brightness(bd, brightness);
  
  	return rc ? rc : count;
  }
  static DEVICE_ATTR_RW(brightness);
  
  static ssize_t type_show(struct device *dev, struct device_attribute *attr,
  		char *buf)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	return sprintf(buf, "%s\n", backlight_types[bd->props.type]);
  }
  static DEVICE_ATTR_RO(type);
  
  static ssize_t max_brightness_show(struct device *dev,
  		struct device_attribute *attr, char *buf)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	return sprintf(buf, "%d\n", bd->props.max_brightness);
  }
  static DEVICE_ATTR_RO(max_brightness);
  
  static ssize_t actual_brightness_show(struct device *dev,
  		struct device_attribute *attr, char *buf)
  {
  	int rc = -ENXIO;
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops && bd->ops->get_brightness) {
  		rc = bd->ops->get_brightness(bd);
  		if (rc >= 0)
  			rc = sprintf(buf, "%d\n", rc);
  	} else {
  		rc = sprintf(buf, "%d\n", bd->props.brightness);
  	}
  	mutex_unlock(&bd->ops_lock);
  
  	return rc;
  }
  static DEVICE_ATTR_RO(actual_brightness);
  
  static ssize_t scale_show(struct device *dev,
  		struct device_attribute *attr, char *buf)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	if (WARN_ON(bd->props.scale > BACKLIGHT_SCALE_NON_LINEAR))
  		return sprintf(buf, "unknown\n");
  
  	return sprintf(buf, "%s\n", backlight_scale_types[bd->props.scale]);
  }
  static DEVICE_ATTR_RO(scale);
  
  static struct class *backlight_class;
  
  #ifdef CONFIG_PM_SLEEP
  static int backlight_suspend(struct device *dev)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
  		bd->props.state |= BL_CORE_SUSPENDED;
  		backlight_update_status(bd);
  	}
  	mutex_unlock(&bd->ops_lock);
  
  	return 0;
  }
  
  static int backlight_resume(struct device *dev)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops && bd->ops->options & BL_CORE_SUSPENDRESUME) {
  		bd->props.state &= ~BL_CORE_SUSPENDED;
  		backlight_update_status(bd);
  	}
  	mutex_unlock(&bd->ops_lock);
  
  	return 0;
  }
  #endif
  
  static SIMPLE_DEV_PM_OPS(backlight_class_dev_pm_ops, backlight_suspend,
  			 backlight_resume);
  
  static void bl_device_release(struct device *dev)
  {
  	struct backlight_device *bd = to_backlight_device(dev);
  	kfree(bd);
  }
  
  static struct attribute *bl_device_attrs[] = {
  	&dev_attr_bl_power.attr,
  	&dev_attr_brightness.attr,
  	&dev_attr_actual_brightness.attr,
  	&dev_attr_max_brightness.attr,
  	&dev_attr_scale.attr,
  	&dev_attr_type.attr,
  	NULL,
  };
  ATTRIBUTE_GROUPS(bl_device);
  
  /**
   * backlight_force_update - tell the backlight subsystem that hardware state
   *   has changed
   * @bd: the backlight device to update
   * @reason: reason for update
   *
   * Updates the internal state of the backlight in response to a hardware event,
   * and generates an uevent to notify userspace. A backlight driver shall call
   * backlight_force_update() when the backlight is changed using, for example,
   * a hot-key. The updated brightness is read using get_brightness() and the
   * brightness value is reported using an uevent.
   */
  void backlight_force_update(struct backlight_device *bd,
  			    enum backlight_update_reason reason)
  {
  	int brightness;
  
  	mutex_lock(&bd->ops_lock);
  	if (bd->ops && bd->ops->get_brightness) {
  		brightness = bd->ops->get_brightness(bd);
  		if (brightness >= 0)
  			bd->props.brightness = brightness;
  		else
  			dev_err(&bd->dev,
  				"Could not update brightness from device: %pe\n",
  				ERR_PTR(brightness));
  	}
  	mutex_unlock(&bd->ops_lock);
  	backlight_generate_event(bd, reason);
  }
  EXPORT_SYMBOL(backlight_force_update);
  
  /* deprecated - use devm_backlight_device_register() */
  struct backlight_device *backlight_device_register(const char *name,
  	struct device *parent, void *devdata, const struct backlight_ops *ops,
  	const struct backlight_properties *props)
  {
  	struct backlight_device *new_bd;
  	int rc;
  
  	pr_debug("backlight_device_register: name=%s\n", name);
  
  	new_bd = kzalloc(sizeof(struct backlight_device), GFP_KERNEL);
  	if (!new_bd)
  		return ERR_PTR(-ENOMEM);
  
  	mutex_init(&new_bd->update_lock);
  	mutex_init(&new_bd->ops_lock);
  
  	new_bd->dev.class = backlight_class;
  	new_bd->dev.parent = parent;
  	new_bd->dev.release = bl_device_release;
  	dev_set_name(&new_bd->dev, "%s", name);
  	dev_set_drvdata(&new_bd->dev, devdata);
  
  	/* Set default properties */
  	if (props) {
  		memcpy(&new_bd->props, props,
  		       sizeof(struct backlight_properties));
  		if (props->type <= 0 || props->type >= BACKLIGHT_TYPE_MAX) {
  			WARN(1, "%s: invalid backlight type", name);
  			new_bd->props.type = BACKLIGHT_RAW;
  		}
  	} else {
  		new_bd->props.type = BACKLIGHT_RAW;
  	}
  
  	rc = device_register(&new_bd->dev);
  	if (rc) {
  		put_device(&new_bd->dev);
  		return ERR_PTR(rc);
  	}
  
  	rc = backlight_register_fb(new_bd);
  	if (rc) {
  		device_unregister(&new_bd->dev);
  		return ERR_PTR(rc);
  	}
  
  	new_bd->ops = ops;
  
  #ifdef CONFIG_PMAC_BACKLIGHT
  	mutex_lock(&pmac_backlight_mutex);
  	if (!pmac_backlight)
  		pmac_backlight = new_bd;
  	mutex_unlock(&pmac_backlight_mutex);
  #endif
  
  	mutex_lock(&backlight_dev_list_mutex);
  	list_add(&new_bd->entry, &backlight_dev_list);
  	mutex_unlock(&backlight_dev_list_mutex);
  
  	blocking_notifier_call_chain(&backlight_notifier,
  				     BACKLIGHT_REGISTERED, new_bd);
  
  	return new_bd;
  }
  EXPORT_SYMBOL(backlight_device_register);
  
  /** backlight_device_get_by_type - find first backlight device of a type
   * @type: the type of backlight device
   *
   * Look up the first backlight device of the specified type
   *
   * RETURNS:
   *
   * Pointer to backlight device if any was found. Otherwise NULL.
   */
  struct backlight_device *backlight_device_get_by_type(enum backlight_type type)
  {
  	bool found = false;
  	struct backlight_device *bd;
  
  	mutex_lock(&backlight_dev_list_mutex);
  	list_for_each_entry(bd, &backlight_dev_list, entry) {
  		if (bd->props.type == type) {
  			found = true;
  			break;
  		}
  	}
  	mutex_unlock(&backlight_dev_list_mutex);
  
  	return found ? bd : NULL;
  }
  EXPORT_SYMBOL(backlight_device_get_by_type);
  
  /**
   * backlight_device_get_by_name - Get backlight device by name
   * @name: Device name
   *
   * This function looks up a backlight device by its name. It obtains a reference
   * on the backlight device and it is the caller's responsibility to drop the
   * reference by calling backlight_put().
   *
   * Returns:
   * A pointer to the backlight device if found, otherwise NULL.
   */
  struct backlight_device *backlight_device_get_by_name(const char *name)
  {
  	struct device *dev;
  
  	dev = class_find_device_by_name(backlight_class, name);
  
  	return dev ? to_backlight_device(dev) : NULL;
  }
  EXPORT_SYMBOL(backlight_device_get_by_name);
  
  /* deprecated - use devm_backlight_device_unregister() */
  void backlight_device_unregister(struct backlight_device *bd)
  {
  	if (!bd)
  		return;
  
  	mutex_lock(&backlight_dev_list_mutex);
  	list_del(&bd->entry);
  	mutex_unlock(&backlight_dev_list_mutex);
  
  #ifdef CONFIG_PMAC_BACKLIGHT
  	mutex_lock(&pmac_backlight_mutex);
  	if (pmac_backlight == bd)
  		pmac_backlight = NULL;
  	mutex_unlock(&pmac_backlight_mutex);
  #endif
  
  	blocking_notifier_call_chain(&backlight_notifier,
  				     BACKLIGHT_UNREGISTERED, bd);
  
  	mutex_lock(&bd->ops_lock);
  	bd->ops = NULL;
  	mutex_unlock(&bd->ops_lock);
  
  	backlight_unregister_fb(bd);
  	device_unregister(&bd->dev);
  }
  EXPORT_SYMBOL(backlight_device_unregister);
  
  static void devm_backlight_device_release(struct device *dev, void *res)
  {
  	struct backlight_device *backlight = *(struct backlight_device **)res;
  
  	backlight_device_unregister(backlight);
  }
  
  static int devm_backlight_device_match(struct device *dev, void *res,
  					void *data)
  {
  	struct backlight_device **r = res;
  
  	return *r == data;
  }
  
  /**
   * backlight_register_notifier - get notified of backlight (un)registration
   * @nb: notifier block with the notifier to call on backlight (un)registration
   *
   * Register a notifier to get notified when backlight devices get registered
   * or unregistered.
   *
   * RETURNS:
   *
   * 0 on success, otherwise a negative error code
   */
  int backlight_register_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_register(&backlight_notifier, nb);
  }
  EXPORT_SYMBOL(backlight_register_notifier);
  
  /**
   * backlight_unregister_notifier - unregister a backlight notifier
   * @nb: notifier block to unregister
   *
   * Register a notifier to get notified when backlight devices get registered
   * or unregistered.
   *
   * RETURNS:
   *
   * 0 on success, otherwise a negative error code
   */
  int backlight_unregister_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_unregister(&backlight_notifier, nb);
  }
  EXPORT_SYMBOL(backlight_unregister_notifier);
  
  /**
   * devm_backlight_device_register - register a new backlight device
   * @dev: the device to register
   * @name: the name of the device
   * @parent: a pointer to the parent device (often the same as @dev)
   * @devdata: an optional pointer to be stored for private driver use
   * @ops: the backlight operations structure
   * @props: the backlight properties
   *
   * Creates and registers new backlight device. When a backlight device
   * is registered the configuration must be specified in the @props
   * parameter. See description of &backlight_properties.
   *
   * RETURNS:
   *
   * struct backlight on success, or an ERR_PTR on error
   */
  struct backlight_device *devm_backlight_device_register(struct device *dev,
  	const char *name, struct device *parent, void *devdata,
  	const struct backlight_ops *ops,
  	const struct backlight_properties *props)
  {
  	struct backlight_device **ptr, *backlight;
  
  	ptr = devres_alloc(devm_backlight_device_release, sizeof(*ptr),
  			GFP_KERNEL);
  	if (!ptr)
  		return ERR_PTR(-ENOMEM);
  
  	backlight = backlight_device_register(name, parent, devdata, ops,
  						props);
  	if (!IS_ERR(backlight)) {
  		*ptr = backlight;
  		devres_add(dev, ptr);
  	} else {
  		devres_free(ptr);
  	}
  
  	return backlight;
  }
  EXPORT_SYMBOL(devm_backlight_device_register);
  
  /**
   * devm_backlight_device_unregister - unregister backlight device
   * @dev: the device to unregister
   * @bd: the backlight device to unregister
   *
   * Deallocates a backlight allocated with devm_backlight_device_register().
   * Normally this function will not need to be called and the resource management
   * code will ensure that the resources are freed.
   */
  void devm_backlight_device_unregister(struct device *dev,
  				struct backlight_device *bd)
  {
  	int rc;
  
  	rc = devres_release(dev, devm_backlight_device_release,
  				devm_backlight_device_match, bd);
  	WARN_ON(rc);
  }
  EXPORT_SYMBOL(devm_backlight_device_unregister);
  
  #ifdef CONFIG_OF
  static int of_parent_match(struct device *dev, const void *data)
  {
  	return dev->parent && dev->parent->of_node == data;
  }
  
  /**
   * of_find_backlight_by_node() - find backlight device by device-tree node
   * @node: device-tree node of the backlight device
   *
   * Returns a pointer to the backlight device corresponding to the given DT
   * node or NULL if no such backlight device exists or if the device hasn't
   * been probed yet.
   *
   * This function obtains a reference on the backlight device and it is the
   * caller's responsibility to drop the reference by calling put_device() on
   * the backlight device's .dev field.
   */
  struct backlight_device *of_find_backlight_by_node(struct device_node *node)
  {
  	struct device *dev;
  
  	dev = class_find_device(backlight_class, NULL, node, of_parent_match);
  
  	return dev ? to_backlight_device(dev) : NULL;
  }
  EXPORT_SYMBOL(of_find_backlight_by_node);
  #endif
  
  static struct backlight_device *of_find_backlight(struct device *dev)
  {
  	struct backlight_device *bd = NULL;
  	struct device_node *np;
  
  	if (!dev)
  		return NULL;
  
  	if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
  		np = of_parse_phandle(dev->of_node, "backlight", 0);
  		if (np) {
  			bd = of_find_backlight_by_node(np);
  			of_node_put(np);
  			if (!bd)
  				return ERR_PTR(-EPROBE_DEFER);
  		}
  	}
  
  	return bd;
  }
  
  static void devm_backlight_release(void *data)
  {
  	struct backlight_device *bd = data;
  
  	put_device(&bd->dev);
  }
  
  /**
   * devm_of_find_backlight - find backlight for a device
   * @dev: the device
   *
   * This function looks for a property named 'backlight' on the DT node
   * connected to @dev and looks up the backlight device. The lookup is
   * device managed so the reference to the backlight device is automatically
   * dropped on driver detach.
   *
   * RETURNS:
   *
   * A pointer to the backlight device if found.
   * Error pointer -EPROBE_DEFER if the DT property is set, but no backlight
   * device is found. NULL if there's no backlight property.
   */
  struct backlight_device *devm_of_find_backlight(struct device *dev)
  {
  	struct backlight_device *bd;
  	int ret;
  
  	bd = of_find_backlight(dev);
  	if (IS_ERR_OR_NULL(bd))
  		return bd;
  	ret = devm_add_action_or_reset(dev, devm_backlight_release, bd);
  	if (ret)
  		return ERR_PTR(ret);
  
  	return bd;
  }
  EXPORT_SYMBOL(devm_of_find_backlight);
  
  static void __exit backlight_class_exit(void)
  {
  	class_destroy(backlight_class);
  }
  
  static int __init backlight_class_init(void)
  {
  	backlight_class = class_create(THIS_MODULE, "backlight");
  	if (IS_ERR(backlight_class)) {
  		pr_warn("Unable to create backlight class; errno = %ld\n",
  			PTR_ERR(backlight_class));
  		return PTR_ERR(backlight_class);
  	}
  
  	backlight_class->dev_groups = bl_device_groups;
  	backlight_class->pm = &backlight_class_dev_pm_ops;
  	INIT_LIST_HEAD(&backlight_dev_list);
  	mutex_init(&backlight_dev_list_mutex);
  	BLOCKING_INIT_NOTIFIER_HEAD(&backlight_notifier);
  
  	return 0;
  }
  
  /*
   * if this is compiled into the kernel, we need to ensure that the
   * class is registered before users of the class try to register lcd's
   */
  postcore_initcall(backlight_class_init);
  module_exit(backlight_class_exit);
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Jamey Hicks <jamey.hicks@hp.com>, Andrew Zabolotny <zap@homelink.ru>");
  MODULE_DESCRIPTION("Backlight Lowlevel Control Abstraction");
  