Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 690 insertions, 0 deletions

diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
new file mode 100644
index 000000000..fc9bb303e
--- /dev/null
+++ b/drivers/video/backlight/backlight.c
@@ -0,0 +1,690 @@
+// 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/slab.h>
+#include <linux/of.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().
+ *
+ * Display drives can control the backlight device's status using
+ * backlight_notify_blank() and backlight_notify_blank_all(). If this
+ * results in a change in the backlight state the functions call the
+ * update_status() operation.
+ */
+
+static struct list_head backlight_dev_list;
+static struct mutex backlight_dev_list_mutex;
+
+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",
+};
+
+void backlight_notify_blank(struct backlight_device *bd, struct device *display_dev,
+			    bool fb_on, bool prev_fb_on)
+{
+	guard(mutex)(&bd->ops_lock);
+
+	if (!bd->ops)
+		return;
+	if (bd->ops->controls_device && !bd->ops->controls_device(bd, display_dev))
+		return;
+
+	if (fb_on && (!prev_fb_on || !bd->use_count)) {
+		if (!bd->use_count++) {
+			bd->props.state &= ~BL_CORE_FBBLANK;
+			backlight_update_status(bd);
+		}
+	} else if (!fb_on && prev_fb_on && bd->use_count) {
+		if (!(--bd->use_count)) {
+			bd->props.state |= BL_CORE_FBBLANK;
+			backlight_update_status(bd);
+		}
+	}
+}
+EXPORT_SYMBOL(backlight_notify_blank);
+
+void backlight_notify_blank_all(struct device *display_dev, bool fb_on, bool prev_fb_on)
+{
+	struct backlight_device *bd;
+
+	guard(mutex)(&backlight_dev_list_mutex);
+
+	list_for_each_entry(bd, &backlight_dev_list, entry)
+		backlight_notify_blank(bd, display_dev, fb_on, prev_fb_on);
+}
+EXPORT_SYMBOL(backlight_notify_blank_all);
+
+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 sysfs_emit(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 sysfs_emit(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 sysfs_emit(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 sysfs_emit(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 = sysfs_emit(buf, "%d\n", rc);
+	} else {
+		rc = sysfs_emit(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 sysfs_emit(buf, "unknown\n");
+
+	return sysfs_emit(buf, "%s\n", backlight_scale_types[bd->props.scale]);
+}
+static DEVICE_ATTR_RO(scale);
+
+#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);
+
+static const struct class backlight_class = {
+	.name = "backlight",
+	.dev_groups = bl_device_groups,
+	.pm = &backlight_class_dev_pm_ops,
+};
+
+/**
+ * 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_obj(struct backlight_device);
+	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);
+	}
+
+	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);
+
+	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 put_device().
+ *
+ * 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
+
+	mutex_lock(&bd->ops_lock);
+	bd->ops = NULL;
+	mutex_unlock(&bd->ops_lock);
+
+	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;
+}
+
+/**
+ * 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_unregister(&backlight_class);
+}
+
+static int __init backlight_class_init(void)
+{
+	int ret;
+
+	ret = class_register(&backlight_class);
+	if (ret) {
+		pr_warn("Unable to create backlight class; errno = %d\n", ret);
+		return ret;
+	}
+
+	INIT_LIST_HEAD(&backlight_dev_list);
+	mutex_init(&backlight_dev_list_mutex);
+
+	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");