path: root/drivers/acpi/acpi_video.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  video.c - ACPI Video Driver
 *
 *  Copyright (C) 2004 Luming Yu <luming.yu@intel.com>
 *  Copyright (C) 2004 Bruno Ducrot <ducrot@poupinou.org>
 *  Copyright (C) 2006 Thomas Tuttle <linux-kernel@ttuttle.net>
 */

#define pr_fmt(fmt) "ACPI: video: " fmt

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/types.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/input.h>
#include <linux/backlight.h>
#include <linux/thermal.h>
#include <linux/sort.h>
#include <linux/pci.h>
#include <linux/pci_ids.h>
#include <linux/slab.h>
#include <linux/dmi.h>
#include <linux/suspend.h>
#include <linux/acpi.h>
#include <acpi/video.h>
#include <linux/uaccess.h>

#define ACPI_VIDEO_BUS_NAME		"Video Bus"
#define ACPI_VIDEO_DEVICE_NAME		"Video Device"

#define MAX_NAME_LEN	20

MODULE_AUTHOR("Bruno Ducrot");
MODULE_DESCRIPTION("ACPI Video Driver");
MODULE_LICENSE("GPL");

static bool brightness_switch_enabled = true;
module_param(brightness_switch_enabled, bool, 0644);

/*
 * By default, we don't allow duplicate ACPI video bus devices
 * under the same VGA controller
 */
static bool allow_duplicates;
module_param(allow_duplicates, bool, 0644);

#define REPORT_OUTPUT_KEY_EVENTS		0x01
#define REPORT_BRIGHTNESS_KEY_EVENTS		0x02
static int report_key_events = -1;
module_param(report_key_events, int, 0644);
MODULE_PARM_DESC(report_key_events,
	"0: none, 1: output changes, 2: brightness changes, 3: all");

static int hw_changes_brightness = -1;
module_param(hw_changes_brightness, int, 0644);
MODULE_PARM_DESC(hw_changes_brightness,
	"Set this to 1 on buggy hw which changes the brightness itself when "
	"a hotkey is pressed: -1: auto, 0: normal 1: hw-changes-brightness");

/*
 * Whether the struct acpi_video_device_attrib::device_id_scheme bit should be
 * assumed even if not actually set.
 */
static bool device_id_scheme = false;
module_param(device_id_scheme, bool, 0444);

static int only_lcd = -1;
module_param(only_lcd, int, 0444);

static bool may_report_brightness_keys;
static int register_count;
static DEFINE_MUTEX(register_count_mutex);
static DEFINE_MUTEX(video_list_lock);
static LIST_HEAD(video_bus_head);
static int acpi_video_bus_add(struct acpi_device *device);
static void acpi_video_bus_remove(struct acpi_device *device);
static void acpi_video_bus_notify(acpi_handle handle, u32 event, void *data);

/*
 * Indices in the _BCL method response: the first two items are special,
 * the rest are all supported levels.
 *
 * See page 575 of the ACPI spec 3.0
 */
enum acpi_video_level_idx {
	ACPI_VIDEO_AC_LEVEL,		/* level when machine has full power */
	ACPI_VIDEO_BATTERY_LEVEL,	/* level when machine is on batteries */
	ACPI_VIDEO_FIRST_LEVEL,		/* actual supported levels begin here */
};

static const struct acpi_device_id video_device_ids[] = {
	{ACPI_VIDEO_HID, 0},
	{"", 0},
};
MODULE_DEVICE_TABLE(acpi, video_device_ids);

static struct acpi_driver acpi_video_bus = {
	.name = "video",
	.class = ACPI_VIDEO_CLASS,
	.ids = video_device_ids,
	.ops = {
		.add = acpi_video_bus_add,
		.remove = acpi_video_bus_remove,
		},
};

struct acpi_video_bus_flags {
	u8 multihead:1;		/* can switch video heads */
	u8 rom:1;		/* can retrieve a video rom */
	u8 post:1;		/* can configure the head to */
	u8 reserved:5;
};

struct acpi_video_bus_cap {
	u8 _DOS:1;		/* Enable/Disable output switching */
	u8 _DOD:1;		/* Enumerate all devices attached to display adapter */
	u8 _ROM:1;		/* Get ROM Data */
	u8 _GPD:1;		/* Get POST Device */
	u8 _SPD:1;		/* Set POST Device */
	u8 _VPO:1;		/* Video POST Options */
	u8 reserved:2;
};

struct acpi_video_device_attrib {
	u32 display_index:4;	/* A zero-based instance of the Display */
	u32 display_port_attachment:4;	/* This field differentiates the display type */
	u32 display_type:4;	/* Describe the specific type in use */
	u32 vendor_specific:4;	/* Chipset Vendor Specific */
	u32 bios_can_detect:1;	/* BIOS can detect the device */
	u32 depend_on_vga:1;	/* Non-VGA output device whose power is related to
				   the VGA device. */
	u32 pipe_id:3;		/* For VGA multiple-head devices. */
	u32 reserved:10;	/* Must be 0 */

	/*
	 * The device ID might not actually follow the scheme described by this
	 * struct acpi_video_device_attrib. If it does, then this bit
	 * device_id_scheme is set; otherwise, other fields should be ignored.
	 *
	 * (but also see the global flag device_id_scheme)
	 */
	u32 device_id_scheme:1;
};

struct acpi_video_enumerated_device {
	union {
		u32 int_val;
		struct acpi_video_device_attrib attrib;
	} value;
	struct acpi_video_device *bind_info;
};

struct acpi_video_bus {
	struct acpi_device *device;
	bool backlight_registered;
	u8 dos_setting;
	struct acpi_video_enumerated_device *attached_array;
	u8 attached_count;
	u8 child_count;
	struct acpi_video_bus_cap cap;
	struct acpi_video_bus_flags flags;
	struct list_head video_device_list;
	struct mutex device_list_lock;	/* protects video_device_list */
	struct list_head entry;
	struct input_dev *input;
	char phys[32];	/* for input device */
	struct notifier_block pm_nb;
};

struct acpi_video_device_flags {
	u8 crt:1;
	u8 lcd:1;
	u8 tvout:1;
	u8 dvi:1;
	u8 bios:1;
	u8 unknown:1;
	u8 notify:1;
	u8 reserved:1;
};

struct acpi_video_device_cap {
	u8 _ADR:1;		/* Return the unique ID */
	u8 _BCL:1;		/* Query list of brightness control levels supported */
	u8 _BCM:1;		/* Set the brightness level */
	u8 _BQC:1;		/* Get current brightness level */
	u8 _BCQ:1;		/* Some buggy BIOS uses _BCQ instead of _BQC */
	u8 _DDC:1;		/* Return the EDID for this device */
};

struct acpi_video_device {
	unsigned long device_id;
	struct acpi_video_device_flags flags;
	struct acpi_video_device_cap cap;
	struct list_head entry;
	struct delayed_work switch_brightness_work;
	int switch_brightness_event;
	struct acpi_video_bus *video;
	struct acpi_device *dev;
	struct acpi_video_device_brightness *brightness;
	struct backlight_device *backlight;
	struct thermal_cooling_device *cooling_dev;
};

static void acpi_video_device_notify(acpi_handle handle, u32 event, void *data);
static void acpi_video_device_rebind(struct acpi_video_bus *video);
static void acpi_video_device_bind(struct acpi_video_bus *video,
				   struct acpi_video_device *device);
static int acpi_video_device_enumerate(struct acpi_video_bus *video);
static int acpi_video_device_lcd_set_level(struct acpi_video_device *device,
			int level);
static int acpi_video_device_lcd_get_level_current(
			struct acpi_video_device *device,
			unsigned long long *level, bool raw);
static int acpi_video_get_next_level(struct acpi_video_device *device,
				     u32 level_current, u32 event);
static void acpi_video_switch_brightness(struct work_struct *work);

/* backlight device sysfs support */
static int acpi_video_get_brightness(struct backlight_device *bd)
{
	unsigned long long cur_level;
	int i;
	struct acpi_video_device *vd = bl_get_data(bd);

	if (acpi_video_device_lcd_get_level_current(vd, &cur_level, false))
		return -EINVAL;
	for (i = ACPI_VIDEO_FIRST_LEVEL; i < vd->brightness->count; i++) {
		if (vd->brightness->levels[i] == cur_level)
			return i - ACPI_VIDEO_FIRST_LEVEL;
	}
	return 0;
}

static int acpi_video_set_brightness(struct backlight_device *bd)
{
	int request_level = bd->props.brightness + ACPI_VIDEO_FIRST_LEVEL;
	struct acpi_video_device *vd = bl_get_data(bd);

	cancel_delayed_work(&vd->switch_brightness_work);
	return acpi_video_device_lcd_set_level(vd,
				vd->brightness->levels[request_level]);
}

static const struct backlight_ops acpi_backlight_ops = {
	.get_brightness = acpi_video_get_brightness,
	.update_status  = acpi_video_set_brightness,
};

/* thermal cooling device callbacks */
static int video_get_max_state(struct thermal_cooling_device *cooling_dev,
			       unsigned long *state)
{
	struct acpi_video_device *video = cooling_dev->devdata;

	*state = video->brightness->count - ACPI_VIDEO_FIRST_LEVEL - 1;
	return 0;
}

static int video_get_cur_state(struct thermal_cooling_device *cooling_dev,
			       unsigned long *state)
{
	struct acpi_video_device *video = cooling_dev->devdata;
	unsigned long long level;
	int offset;

	if (acpi_video_device_lcd_get_level_current(video, &level, false))
		return -EINVAL;
	for (offset = ACPI_VIDEO_FIRST_LEVEL; offset < video->brightness->count;
	     offset++)
		if (level == video->brightness->levels[offset]) {
			*state = video->brightness->count - offset - 1;
			return 0;
		}

	return -EINVAL;
}

static int
video_set_cur_state(struct thermal_cooling_device *cooling_dev, unsigned long state)
{
	struct acpi_video_device *video = cooling_dev->devdata;
	int level;

	if (state >= video->brightness->count - ACPI_VIDEO_FIRST_LEVEL)
		return -EINVAL;

	state = video->brightness->count - state;
	level = video->brightness->levels[state - 1];
	return acpi_video_device_lcd_set_level(video, level);
}

static const struct thermal_cooling_device_ops video_cooling_ops = {
	.get_max_state = video_get_max_state,
	.get_cur_state = video_get_cur_state,
	.set_cur_state = video_set_cur_state,
};

/*
 * --------------------------------------------------------------------------
 *                             Video Management
 * --------------------------------------------------------------------------
 */

static int
acpi_video_device_lcd_query_levels(acpi_handle handle,
				   union acpi_object **levels)
{
	int status;
	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
	union acpi_object *obj;


	*levels = NULL;

	status = acpi_evaluate_object(handle, "_BCL", NULL, &buffer);
	if (ACPI_FAILURE(status))
		return status;
	obj = (union acpi_object *)buffer.pointer;
	if (!obj || (obj->type != ACPI_TYPE_PACKAGE)) {
		acpi_handle_info(handle, "Invalid _BCL data\n");
		status = -EFAULT;
		goto err;
	}

	*levels = obj;

	return 0;

err:
	kfree(buffer.pointer);

	return status;
}

static int
acpi_video_device_lcd_set_level(struct acpi_video_device *device, int level)
{
	int status;
	int state;

	status = acpi_execute_simple_method(device->dev->handle,
					    "_BCM", level);
	if (ACPI_FAILURE(status)) {
		acpi_handle_info(device->dev->handle, "_BCM evaluation failed\n");
		return -EIO;
	}

	device->brightness->curr = level;
	for (state = ACPI_VIDEO_FIRST_LEVEL; state < device->brightness->count;
	     state++)
		if (level == device->brightness->levels[state]) {
			if (device->backlight)
				device->backlight->props.brightness =
					state - ACPI_VIDEO_FIRST_LEVEL;
			return 0;
		}

	acpi_handle_info(device->dev->handle, "Current brightness invalid\n");
	return -EINVAL;
}

/*
 * For some buggy _BQC methods, we need to add a constant value to
 * the _BQC return value to get the actual current brightness level
 */

static int bqc_offset_aml_bug_workaround;
static int video_set_bqc_offset(const struct dmi_system_id *d)
{
	bqc_offset_aml_bug_workaround = 9;
	return 0;
}

static int video_set_device_id_scheme(const struct dmi_system_id *d)
{
	device_id_scheme = true;
	return 0;
}

static int video_enable_only_lcd(const struct dmi_system_id *d)
{
	only_lcd = true;
	return 0;
}

static int video_set_report_key_events(const struct dmi_system_id *id)
{
	if (report_key_events == -1)
		report_key_events = (uintptr_t)id->driver_data;
	return 0;
}

static int video_hw_changes_brightness(
	const struct dmi_system_id *d)
{
	if (hw_changes_brightness == -1)
		hw_changes_brightness = 1;
	return 0;
}

static const struct dmi_system_id video_dmi_table[] = {
	/*
	 * Broken _BQC workaround http://bugzilla.kernel.org/show_bug.cgi?id=13121
	 */
	{
	 .callback = video_set_bqc_offset,
	 .ident = "Acer Aspire 5720",
	 .matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5720"),
		},
	},
	{
	 .callback = video_set_bqc_offset,
	 .ident = "Acer Aspire 5710Z",
	 .matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5710Z"),
		},
	},
	{
	 .callback = video_set_bqc_offset,
	 .ident = "eMachines E510",
	 .matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "EMACHINES"),
		DMI_MATCH(DMI_PRODUCT_NAME, "eMachines E510"),
		},
	},
	{
	 .callback = video_set_bqc_offset,
	 .ident = "Acer Aspire 5315",
	 .matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 5315"),
		},
	},
	{
	 .callback = video_set_bqc_offset,
	 .ident = "Acer Aspire 7720",
	 .matches = {
		DMI_MATCH(DMI_BOARD_VENDOR, "Acer"),
		DMI_MATCH(DMI_PRODUCT_NAME, "Aspire 7720"),
		},
	},

	/*
	 * Some machine's _DOD IDs don't have bit 31(Device ID Scheme) set
	 * but the IDs actually follow the Device ID Scheme.
	 */
	{
	 /* https://bugzilla.kernel.org/show_bug.cgi?id=104121 */
	 .callback = video_set_device_id_scheme,
	 .ident = "ESPRIMO Mobile M9410",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "FUJITSU SIEMENS"),
		DMI_MATCH(DMI_PRODUCT_NAME, "ESPRIMO Mobile M9410"),
		},
	},
	/*
	 * Some machines have multiple video output devices, but only the one
	 * that is the type of LCD can do the backlight control so we should not
	 * register backlight interface for other video output devices.
	 */
	{
	 /* https://bugzilla.kernel.org/show_bug.cgi?id=104121 */
	 .callback = video_enable_only_lcd,
	 .ident = "ESPRIMO Mobile M9410",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "FUJITSU SIEMENS"),
		DMI_MATCH(DMI_PRODUCT_NAME, "ESPRIMO Mobile M9410"),
		},
	},
	/*
	 * Some machines report wrong key events on the acpi-bus, suppress
	 * key event reporting on these.  Note this is only intended to work
	 * around events which are plain wrong. In some cases we get double
	 * events, in this case acpi-video is considered the canonical source
	 * and the events from the other source should be filtered. E.g.
	 * by calling acpi_video_handles_brightness_key_presses() from the
	 * vendor acpi/wmi driver or by using /lib/udev/hwdb.d/60-keyboard.hwdb
	 */
	{
	 .callback = video_set_report_key_events,
	 .driver_data = (void *)((uintptr_t)REPORT_OUTPUT_KEY_EVENTS),
	 .ident = "Dell Vostro V131",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "Vostro V131"),
		},
	},
	{
	 .callback = video_set_report_key_events,
	 .driver_data = (void *)((uintptr_t)REPORT_BRIGHTNESS_KEY_EVENTS),
	 .ident = "Dell Vostro 3350",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
		DMI_MATCH(DMI_PRODUCT_NAME, "Vostro 3350"),
		},
	},
	{
	 .callback = video_set_report_key_events,
	 .driver_data = (void *)((uintptr_t)REPORT_BRIGHTNESS_KEY_EVENTS),
	 .ident = "COLORFUL X15 AT 23",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "COLORFUL"),
		DMI_MATCH(DMI_PRODUCT_NAME, "X15 AT 23"),
		},
	},
	/*
	 * Some machines change the brightness themselves when a brightness
	 * hotkey gets pressed, despite us telling them not to. In this case
	 * acpi_video_device_notify() should only call backlight_force_update(
	 * BACKLIGHT_UPDATE_HOTKEY) and not do anything else.
	 */
	{
	 /* https://bugzilla.kernel.org/show_bug.cgi?id=204077 */
	 .callback = video_hw_changes_brightness,
	 .ident = "Packard Bell EasyNote MZ35",
	 .matches = {
		DMI_MATCH(DMI_SYS_VENDOR, "Packard Bell"),
		DMI_MATCH(DMI_PRODUCT_NAME, "EasyNote MZ35"),
		},
	},
	{}
};

static unsigned long long
acpi_video_bqc_value_to_level(struct acpi_video_device *device,
			      unsigned long long bqc_value)
{
	unsigned long long level;

	if (device->brightness->flags._BQC_use_index) {
		/*
		 * _BQC returns an index that doesn't account for the first 2
		 * items with special meaning (see enum acpi_video_level_idx),
		 * so we need to compensate for that by offsetting ourselves
		 */
		if (device->brightness->flags._BCL_reversed)
			bqc_value = device->brightness->count -
				ACPI_VIDEO_FIRST_LEVEL - 1 - bqc_value;

		level = device->brightness->levels[bqc_value +
						   ACPI_VIDEO_FIRST_LEVEL];
	} else {
		level = bqc_value;
	}

	level += bqc_offset_aml_bug_workaround;

	return level;
}

static int
acpi_video_device_lcd_get_level_current(struct acpi_video_device *device,
					unsigned long long *level, bool raw)
{
	acpi_status status = AE_OK;
	int i;

	if (device->cap._BQC || device->cap._BCQ) {
		char *buf = device->cap._BQC ? "_BQC" : "_BCQ";

		status = acpi_evaluate_integer(device->dev->handle, buf,
						NULL, level);
		if (ACPI_SUCCESS(status)) {
			if (raw) {
				/*
				 * Caller has indicated he wants the raw
				 * value returned by _BQC, so don't furtherly
				 * mess with the value.
				 */
				return 0;
			}

			*level = acpi_video_bqc_value_to_level(device, *level);

			for (i = ACPI_VIDEO_FIRST_LEVEL;
			     i < device->brightness->count; i++)
				if (device->brightness->levels[i] == *level) {
					device->brightness->curr = *level;
					return 0;
				}
			/*
			 * BQC returned an invalid level.
			 * Stop using it.
			 */
			acpi_handle_info(device->dev->handle,
					 "%s returned an invalid level", buf);
			device->cap._BQC = device->cap._BCQ = 0;
		} else {
			/*
			 * Fixme:
			 * should we return an error or ignore this failure?
			 * dev->brightness->curr is a cached value which stores
			 * the correct current backlight level in most cases.
			 * ACPI video backlight still works w/ buggy _BQC.
			 * http://bugzilla.kernel.org/show_bug.cgi?id=12233
			 */
			acpi_handle_info(device->dev->handle,
					 "%s evaluation failed", buf);
			device->cap._BQC = device->cap._BCQ = 0;
		}
	}

	*level = device->brightness->curr;
	return 0;
}

static int
acpi_video_device_EDID(struct acpi_video_device *device,
		       union acpi_object **edid, ssize_t length)
{
	int status;
	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
	union acpi_object *obj;
	union acpi_object arg0 = { ACPI_TYPE_INTEGER };
	struct acpi_object_list args = { 1, &arg0 };


	*edid = NULL;

	if (!device)
		return -ENODEV;
	if (length == 128)
		arg0.integer.value = 1;
	else if (length == 256)
		arg0.integer.value = 2;
	else
		return -EINVAL;

	status = acpi_evaluate_object(device->dev->handle, "_DDC", &args, &buffer);
	if (ACPI_FAILURE(status))
		return -ENODEV;

	obj = buffer.pointer;

	if (obj && obj->type == ACPI_TYPE_BUFFER)
		*edid = obj;
	else {
		acpi_handle_info(device->dev->handle, "Invalid _DDC data\n");
		status = -EFAULT;
		kfree(obj);
	}

	return status;
}

/* bus */

/*
 *  Arg:
 *	video		: video bus device pointer
 *	bios_flag	:
 *		0.	The system BIOS should NOT automatically switch(toggle)
 *			the active display output.
 *		1.	The system BIOS should automatically switch (toggle) the
 *			active display output. No switch event.
 *		2.	The _DGS value should be locked.
 *		3.	The system BIOS should not automatically switch (toggle) the
 *			active display output, but instead generate the display switch
 *			event notify code.
 *	lcd_flag	:
 *		0.	The system BIOS should automatically control the brightness level
 *			of the LCD when:
 *			- the power changes from AC to DC (ACPI appendix B)
 *			- a brightness hotkey gets pressed (implied by Win7/8 backlight docs)
 *		1.	The system BIOS should NOT automatically control the brightness
 *			level of the LCD when:
 *			- the power changes from AC to DC (ACPI appendix B)
 *			- a brightness hotkey gets pressed (implied by Win7/8 backlight docs)
 *  Return Value:
 *		-EINVAL	wrong arg.
 */

static int
acpi_video_bus_DOS(struct acpi_video_bus *video, int bios_flag, int lcd_flag)
{
	acpi_status status;

	if (!video->cap._DOS)
		return 0;

	if (bios_flag < 0 || bios_flag > 3 || lcd_flag < 0 || lcd_flag > 1)
		return -EINVAL;
	video->dos_setting = (lcd_flag << 2) | bios_flag;
	status = acpi_execute_simple_method(video->device->handle, "_DOS",
					    (lcd_flag << 2) | bios_flag);
	if (ACPI_FAILURE(status))
		return -EIO;

	return 0;
}

/*
 * Simple comparison function used to sort backlight levels.
 */

static int
acpi_video_cmp_level(const void *a, const void *b)
{
	return *(int *)a - *(int *)b;
}

/*
 * Decides if _BQC/_BCQ for this system is usable
 *
 * We do this by changing the level first and then read out the current
 * brightness level, if the value does not match, find out if it is using
 * index. If not, clear the _BQC/_BCQ capability.
 */
static int acpi_video_bqc_quirk(struct acpi_video_device *device,
				int max_level, int current_level)
{
	struct acpi_video_device_brightness *br = device->brightness;
	int result;
	unsigned long long level;
	int test_level;

	/* don't mess with existing known broken systems */
	if (bqc_offset_aml_bug_workaround)
		return 0;

	/*
	 * Some systems always report current brightness level as maximum
	 * through _BQC, we need to test another value for them. However,
	 * there is a subtlety:
	 *
	 * If the _BCL package ordering is descending, the first level
	 * (br->levels[2]) is likely to be 0, and if the number of levels
	 * matches the number of steps, we might confuse a returned level to
	 * mean the index.
	 *
	 * For example:
	 *
	 *     current_level = max_level = 100
	 *     test_level = 0
	 *     returned level = 100
	 *
	 * In this case 100 means the level, not the index, and _BCM failed.
	 * Still, if the _BCL package ordering is descending, the index of
	 * level 0 is also 100, so we assume _BQC is indexed, when it's not.
	 *
	 * This causes all _BQC calls to return bogus values causing weird
	 * behavior from the user's perspective.  For example:
	 *
	 * xbacklight -set 10; xbacklight -set 20;
	 *
	 * would flash to 90% and then slowly down to the desired level (20).
	 *
	 * The solution is simple; test anything other than the first level
	 * (e.g. 1).
	 */
	test_level = current_level == max_level
		? br->levels[ACPI_VIDEO_FIRST_LEVEL + 1]
		: max_level;

	result = acpi_video_device_lcd_set_level(device, test_level);
	if (result)
		return result;

	result = acpi_video_device_lcd_get_level_current(device, &level, true);
	if (result)
		return result;

	if (level != test_level) {
		/* buggy _BQC found, need to find out if it uses index */
		if (level < br->count) {
			if (br->flags._BCL_reversed)
				level = br->count - ACPI_VIDEO_FIRST_LEVEL - 1 - level;
			if (br->levels[level + ACPI_VIDEO_FIRST_LEVEL] == test_level)
				br->flags._BQC_use_index = 1;
		}

		if (!br->flags._BQC_use_index)
			device->cap._BQC = device->cap._BCQ = 0;
	}

	return 0;
}

int acpi_video_get_levels(struct acpi_device *device,
			  struct acpi_video_device_brightness **dev_br,
			  int *pmax_level)
{
	union acpi_object *obj = NULL;
	int i, max_level = 0, count = 0, level_ac_battery = 0;
	union acpi_object *o;
	struct acpi_video_device_brightness *br = NULL;
	int result = 0;
	u32 value;

	if (ACPI_FAILURE(acpi_video_device_lcd_query_levels(device->handle, &obj))) {
		acpi_handle_debug(device->handle,
				  "Could not query available LCD brightness level\n");
		result = -ENODEV;
		goto out;
	}

	if (obj->package.count < ACPI_VIDEO_FIRST_LEVEL) {
		result = -EINVAL;
		goto out;
	}

	br = kzalloc(sizeof(*br), GFP_KERNEL);
	if (!br) {
		result = -ENOMEM;
		goto out;
	}

	/*
	 * Note that we have to reserve 2 extra items (ACPI_VIDEO_FIRST_LEVEL),
	 * in order to account for buggy BIOS which don't export the first two
	 * special levels (see below)
	 */
	br->levels = kmalloc_array(obj->package.count + ACPI_VIDEO_FIRST_LEVEL,
				   sizeof(*br->levels),
				   GFP_KERNEL);
	if (!br->levels) {
		result = -ENOMEM;
		goto out_free;
	}

	for (i = 0; i < obj->package.count; i++) {
		o = (union acpi_object *)&obj->package.elements[i];
		if (o->type != ACPI_TYPE_INTEGER) {
			acpi_handle_info(device->handle, "Invalid data\n");
			continue;
		}
		value = (u32) o->integer.value;
		/* Skip duplicate entries */
		if (count > ACPI_VIDEO_FIRST_LEVEL
		    && br->levels[count - 1] == value)
			continue;

		br->levels[count] = value;

		if (br->levels[count] > max_level)
			max_level = br->levels[count];
		count++;
	}

	/*
	 * some buggy BIOS don't export the levels
	 * when machine is on AC/Battery in _BCL package.
	 * In this case, the first two elements in _BCL packages
	 * are also supported brightness levels that OS should take care of.
	 */
	for (i = ACPI_VIDEO_FIRST_LEVEL; i < count; i++) {
		if (br->levels[i] == br->levels[ACPI_VIDEO_AC_LEVEL])
			level_ac_battery++;
		if (br->levels[i] == br->levels[ACPI_VIDEO_BATTERY_LEVEL])
			level_ac_battery++;
	}

	if (level_ac_battery < ACPI_VIDEO_FIRST_LEVEL) {
		level_ac_battery = ACPI_VIDEO_FIRST_LEVEL - level_ac_battery;
		br->flags._BCL_no_ac_battery_levels = 1;
		for (i = (count - 1 + level_ac_battery);
		     i >= ACPI_VIDEO_FIRST_LEVEL; i--)
			br->levels[i] = br->levels[i - level_ac_battery];
		count += level_ac_battery;
	} else if (level_ac_battery > ACPI_VIDEO_FIRST_LEVEL)
		acpi_handle_info(device->handle,
				 "Too many duplicates in _BCL package");

	/* Check if the _BCL package is in a reversed order */
	if (max_level == br->levels[ACPI_VIDEO_FIRST_LEVEL]) {
		br->flags._BCL_reversed = 1;
		sort(&br->levels[ACPI_VIDEO_FIRST_LEVEL],
		     count - ACPI_VIDEO_FIRST_LEVEL,
		     sizeof(br->levels[ACPI_VIDEO_FIRST_LEVEL]),
		     acpi_video_cmp_level, NULL);
	} else if (max_level != br->levels[count - 1])
		acpi_handle_info(device->handle,
				 "Found unordered _BCL package");

	br->count = count;
	*dev_br = br;
	if (pmax_level)
		*pmax_level = max_level;

out:
	kfree(obj);
	return result;
out_free:
	kfree(br);
	goto out;
}
EXPORT_SYMBOL(acpi_video_get_levels);

/*
 *  Arg:
 *	device	: video output device (LCD, CRT, ..)
 *
 *  Return Value:
 *	Maximum brightness level
 *
 *  Allocate and initialize device->brightness.
 */

static int
acpi_video_init_brightness(struct acpi_video_device *device)
{
	int i, max_level = 0;
	unsigned long long level, level_old;
	struct acpi_video_device_brightness *br = NULL;
	int result;

	result = acpi_video_get_levels(device->dev, &br, &max_level);
	if (result)
		return result;
	device->brightness = br;

	/* _BQC uses INDEX while _BCL uses VALUE in some laptops */
	br->curr = level = max_level;

	if (!device->cap._BQC)
		goto set_level;

	result = acpi_video_device_lcd_get_level_current(device,
							 &level_old, true);
	if (result)
		goto out_free_levels;

	result = acpi_video_bqc_quirk(device, max_level, level_old);
	if (result)
		goto out_free_levels;
	/*
	 * cap._BQC may get cleared due to _BQC is found to be broken
	 * in acpi_video_bqc_quirk, so check again here.
	 */
	if (!device->cap._BQC)
		goto set_level;

	level = acpi_video_bqc_value_to_level(device, level_old);
	/*
	 * On some buggy laptops, _BQC returns an uninitialized
	 * value when invoked for the first time, i.e.
	 * level_old is invalid (no matter whether it's a level
	 * or an index). Set the backlight to max_level in this case.
	 */
	for (i = ACPI_VIDEO_FIRST_LEVEL; i < br->count; i++)
		if (level == br->levels[i])
			break;
	if (i == br->count || !level)
		level = max_level;

set_level:
	result = acpi_video_device_lcd_set_level(device, level);
	if (result)
		goto out_free_levels;

	acpi_handle_debug(device->dev->handle, "found %d brightness levels\n",
			  br->count - ACPI_VIDEO_FIRST_LEVEL);

	return 0;

out_free_levels:
	kfree(br->levels);
	kfree(br);
	device->brightness = NULL;
	return result;
}

/*
 *  Arg:
 *	device	: video output device (LCD, CRT, ..)
 *
 *  Return Value:
 *	None
 *
 *  Find out all required AML methods defined under the output
 *  device.
 */

static void acpi_video_device_find_cap(struct acpi_video_device *device)
{
	if (acpi_has_method(device->dev->handle, "_ADR"))
		device->cap._ADR = 1;
	if (acpi_has_method(device->dev->handle, "_BCL"))
		device->cap._BCL = 1;
	if (acpi_has_method(device->dev->handle, "_BCM"))
		device->cap._BCM = 1;
	if (acpi_has_method(device->dev->handle, "_BQC")) {
		device->cap._BQC = 1;
	} else if (acpi_has_method(device->dev->handle, "_BCQ")) {
		acpi_handle_info(device->dev->handle,
				 "_BCQ is used instead of _BQC\n");
		device->cap._BCQ = 1;
	}

	if (acpi_has_method(device->dev->handle, "_DDC"))
		device->cap._DDC = 1;
}

/*
 *  Arg:
 *	device	: video output device (VGA)
 *
 *  Return Value:
 *	None
 *
 *  Find out all required AML methods defined under the video bus device.
 */

static void acpi_video_bus_find_cap(struct acpi_video_bus *video)
{
	if (acpi_has_method(video->device->handle, "_DOS"))
		video->cap._DOS = 1;
	if (acpi_has_method(video->device->handle, "_DOD"))
		video->cap._DOD = 1;
	if (acpi_has_method(video->device->handle, "_ROM"))
		video->cap._ROM = 1;
	if (acpi_has_method(video->device->handle, "_GPD"))
		video->cap._GPD = 1;
	if (acpi_has_method(video->device->handle, "_SPD"))
		video->cap._SPD = 1;
	if (acpi_has_method(video->device->handle, "_VPO"))
		video->cap._VPO = 1;
}

/*
 * Check whether the video bus device has required AML method to
 * support the desired features
 */

static int acpi_video_bus_check(struct acpi_video_bus *video)
{
	acpi_status status = -ENOENT;
	struct pci_dev *dev;

	if (!video)
		return -EINVAL;

	dev = acpi_get_pci_dev(video->device->handle);
	if (!dev)
		return -ENODEV;
	pci_dev_put(dev);

	/*
	 * Since there is no HID, CID and so on for VGA driver, we have
	 * to check well known required nodes.
	 */

	/* Does this device support video switching? */
	if (video->cap._DOS || video->cap._DOD) {
		if (!video->cap._DOS) {
			pr_info(FW_BUG "ACPI(%s) defines _DOD but not _DOS\n",
				acpi_device_bid(video->device));
		}
		video->flags.multihead = 1;
		status = 0;
	}

	/* Does this device support retrieving a video ROM? */
	if (video->cap._ROM) {
		video->flags.rom = 1;
		status = 0;
	}

	/* Does this device support configuring which video device to POST? */
	if (video->cap._GPD && video->cap._SPD && video->cap._VPO) {
		video->flags.post = 1;
		status = 0;
	}

	return status;
}

/*
 * --------------------------------------------------------------------------
 *                               Driver Interface
 * --------------------------------------------------------------------------
 */

/* device interface */
static struct acpi_video_device_attrib *
acpi_video_get_device_attr(struct acpi_video_bus *video, unsigned long device_id)
{
	struct acpi_video_enumerated_device *ids;
	int i;

	for (i = 0; i < video->attached_count; i++) {
		ids = &video->attached_array[i];
		if ((ids->value.int_val & 0xffff) == device_id)
			return &ids->value.attrib;
	}

	return NULL;
}

static int
acpi_video_get_device_type(struct acpi_video_bus *video,
			   unsigned long device_id)
{
	struct acpi_video_enumerated_device *ids;
	int i;

	for (i = 0; i < video->attached_count; i++) {
		ids = &video->attached_array[i];
		if ((ids->value.int_val & 0xffff) == device_id)
			return ids->value.int_val;
	}

	return 0;
}

static int acpi_video_bus_get_one_device(struct acpi_device *device, void *arg)
{
	struct acpi_video_bus *video = arg;
	struct acpi_video_device_attrib *attribute;
	struct acpi_video_device *data;
	unsigned long long device_id;
	acpi_status status;
	int device_type;

	status = acpi_evaluate_integer(device->handle, "_ADR", NULL, &device_id);
	/* Skip devices without _ADR instead of failing. */
	if (ACPI_FAILURE(status))
		goto exit;

	data = kzalloc(sizeof(struct acpi_video_device), GFP_KERNEL);
	if (!data) {
		dev_dbg(&device->dev, "Cannot attach\n");
		return -ENOMEM;
	}

	strcpy(acpi_device_name(device), ACPI_VIDEO_DEVICE_NAME);
	strcpy(acpi_device_class(device), ACPI_VIDEO_CLASS);

	data->device_id = device_id;
	data->video = video;
	data->dev = device;
	INIT_DELAYED_WORK(&data->switch_brightness_work,
			  acpi_video_switch_brightness);

	attribute = acpi_video_get_device_attr(video, device_id);

	if (attribute && (attribute->device_id_scheme || device_id_scheme)) {
		switch (attribute->display_type) {
		case ACPI_VIDEO_DISPLAY_CRT:
			data->flags.crt = 1;
			break;
		case ACPI_VIDEO_DISPLAY_TV:
			data->flags.tvout = 1;
			break;
		case ACPI_VIDEO_DISPLAY_DVI:
			data->flags.dvi = 1;
			break;
		case ACPI_VIDEO_DISPLAY_LCD:
			data->flags.lcd = 1;
			break;
		default:
			data->flags.unknown = 1;
			break;
		}
		if (attribute->bios_can_detect)
			data->flags.bios = 1;
	} else {
		/* Check for legacy IDs */
		device_type = acpi_video_get_device_type(video, device_id);
		/* Ignore bits 16 and 18-20 */
		switch (device_type & 0xffe2ffff) {
		case ACPI_VIDEO_DISPLAY_LEGACY_MONITOR:
			data->flags.crt = 1;
			break;
		case ACPI_VIDEO_DISPLAY_LEGACY_PANEL:
			data->flags.lcd = 1;
			break;
		case ACPI_VIDEO_DISPLAY_LEGACY_TV:
			data->flags.tvout = 1;
			break;
		default:
			data->flags.unknown = 1;
		}
	}

	acpi_video_device_bind(video, data);
	acpi_video_device_find_cap(data);

	if (data->cap._BCM && data->cap._BCL)
		may_report_brightness_keys = true;

	mutex_lock(&video->device_list_lock);
	list_add_tail(&data->entry, &video->video_device_list);
	mutex_unlock(&video->device_list_lock);

exit:
	video->child_count++;
	return 0;
}

/*
 *  Arg:
 *	video	: video bus device
 *
 *  Return:
 *	none
 *
 *  Enumerate the video device list of the video bus,
 *  bind the ids with the corresponding video devices
 *  under the video bus.
 */

static void acpi_video_device_rebind(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev;

	mutex_lock(&video->device_list_lock);

	list_for_each_entry(dev, &video->video_device_list, entry)
		acpi_video_device_bind(video, dev);

	mutex_unlock(&video->device_list_lock);
}

/*
 *  Arg:
 *	video	: video bus device
 *	device	: video output device under the video
 *		bus
 *
 *  Return:
 *	none
 *
 *  Bind the ids with the corresponding video devices
 *  under the video bus.
 */

static void
acpi_video_device_bind(struct acpi_video_bus *video,
		       struct acpi_video_device *device)
{
	struct acpi_video_enumerated_device *ids;
	int i;

	for (i = 0; i < video->attached_count; i++) {
		ids = &video->attached_array[i];
		if (device->device_id == (ids->value.int_val & 0xffff)) {
			ids->bind_info = device;
			acpi_handle_debug(video->device->handle, "%s: %d\n",
					  __func__, i);
		}
	}
}

static bool acpi_video_device_in_dod(struct acpi_video_device *device)
{
	struct acpi_video_bus *video = device->video;
	int i;

	/*
	 * If we have a broken _DOD or we have more than 8 output devices
	 * under the graphics controller node that we can't proper deal with
	 * in the operation region code currently, no need to test.
	 */
	if (!video->attached_count || video->child_count > 8)
		return true;

	for (i = 0; i < video->attached_count; i++) {
		if ((video->attached_array[i].value.int_val & 0xfff) ==
		    (device->device_id & 0xfff))
			return true;
	}

	return false;
}

/*
 *  Arg:
 *	video	: video bus device
 *
 *  Return:
 *	< 0	: error
 *
 *  Call _DOD to enumerate all devices attached to display adapter
 *
 */

static int acpi_video_device_enumerate(struct acpi_video_bus *video)
{
	int status;
	int count;
	int i;
	struct acpi_video_enumerated_device *active_list;
	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
	union acpi_object *dod = NULL;
	union acpi_object *obj;

	if (!video->cap._DOD)
		return AE_NOT_EXIST;

	status = acpi_evaluate_object(video->device->handle, "_DOD", NULL, &buffer);
	if (ACPI_FAILURE(status)) {
		acpi_handle_info(video->device->handle,
				 "_DOD evaluation failed: %s\n",
				 acpi_format_exception(status));
		return status;
	}

	dod = buffer.pointer;
	if (!dod || (dod->type != ACPI_TYPE_PACKAGE)) {
		acpi_handle_info(video->device->handle, "Invalid _DOD data\n");
		status = -EFAULT;
		goto out;
	}

	acpi_handle_debug(video->device->handle, "Found %d video heads in _DOD\n",
			  dod->package.count);

	active_list = kcalloc(1 + dod->package.count,
			      sizeof(struct acpi_video_enumerated_device),
			      GFP_KERNEL);
	if (!active_list) {
		status = -ENOMEM;
		goto out;
	}

	count = 0;
	for (i = 0; i < dod->package.count; i++) {
		obj = &dod->package.elements[i];

		if (obj->type != ACPI_TYPE_INTEGER) {
			acpi_handle_info(video->device->handle,
					 "Invalid _DOD data in element %d\n", i);
			continue;
		}

		active_list[count].value.int_val = obj->integer.value;
		active_list[count].bind_info = NULL;

		acpi_handle_debug(video->device->handle,
				  "_DOD element[%d] = %d\n", i,
				  (int)obj->integer.value);

		count++;
	}

	kfree(video->attached_array);

	video->attached_array = active_list;
	video->attached_count = count;

out:
	kfree(buffer.pointer);
	return status;
}

static int
acpi_video_get_next_level(struct acpi_video_device *device,
			  u32 level_current, u32 event)
{
	int min, max, min_above, max_below, i, l, delta = 255;
	max = max_below = 0;
	min = min_above = 255;
	/* Find closest level to level_current */
	for (i = ACPI_VIDEO_FIRST_LEVEL; i < device->brightness->count; i++) {
		l = device->brightness->levels[i];
		if (abs(l - level_current) < abs(delta)) {
			delta = l - level_current;
			if (!delta)
				break;
		}
	}
	/* Adjust level_current to closest available level */
	level_current += delta;
	for (i = ACPI_VIDEO_FIRST_LEVEL; i < device->brightness->count; i++) {
		l = device->brightness->levels[i];
		if (l < min)
			min = l;
		if (l > max)
			max = l;
		if (l < min_above && l > level_current)
			min_above = l;
		if (l > max_below && l < level_current)
			max_below = l;
	}

	switch (event) {
	case ACPI_VIDEO_NOTIFY_CYCLE_BRIGHTNESS:
		return (level_current < max) ? min_above : min;
	case ACPI_VIDEO_NOTIFY_INC_BRIGHTNESS:
		return (level_current < max) ? min_above : max;
	case ACPI_VIDEO_NOTIFY_DEC_BRIGHTNESS:
		return (level_current > min) ? max_below : min;
	case ACPI_VIDEO_NOTIFY_ZERO_BRIGHTNESS:
	case ACPI_VIDEO_NOTIFY_DISPLAY_OFF:
		return 0;
	default:
		return level_current;
	}
}

static void
acpi_video_switch_brightness(struct work_struct *work)
{
	struct acpi_video_device *device = container_of(to_delayed_work(work),
			     struct acpi_video_device, switch_brightness_work);
	unsigned long long level_current, level_next;
	int event = device->switch_brightness_event;
	int result = -EINVAL;

	/* no warning message if acpi_backlight=vendor or a quirk is used */
	if (!device->backlight)
		return;

	if (!device->brightness)
		goto out;

	result = acpi_video_device_lcd_get_level_current(device,
							 &level_current,
							 false);
	if (result)
		goto out;

	level_next = acpi_video_get_next_level(device, level_current, event);

	result = acpi_video_device_lcd_set_level(device, level_next);

	if (!result)
		backlight_force_update(device->backlight,
				       BACKLIGHT_UPDATE_HOTKEY);

out:
	if (result)
		acpi_handle_info(device->dev->handle,
				 "Failed to switch brightness\n");
}

int acpi_video_get_edid(struct acpi_device *device, int type, int device_id,
			void **edid)
{
	struct acpi_video_bus *video;
	struct acpi_video_device *video_device;
	union acpi_object *buffer = NULL;
	acpi_status status;
	int i, length;

	if (!device || !acpi_driver_data(device))
		return -EINVAL;

	video = acpi_driver_data(device);

	for (i = 0; i < video->attached_count; i++) {
		video_device = video->attached_array[i].bind_info;
		length = 256;

		if (!video_device)
			continue;

		if (!video_device->cap._DDC)
			continue;

		if (type) {
			switch (type) {
			case ACPI_VIDEO_DISPLAY_CRT:
				if (!video_device->flags.crt)
					continue;
				break;
			case ACPI_VIDEO_DISPLAY_TV:
				if (!video_device->flags.tvout)
					continue;
				break;
			case ACPI_VIDEO_DISPLAY_DVI:
				if (!video_device->flags.dvi)
					continue;
				break;
			case ACPI_VIDEO_DISPLAY_LCD:
				if (!video_device->flags.lcd)
					continue;
				break;
			}
		} else if (video_device->device_id != device_id) {
			continue;
		}

		status = acpi_video_device_EDID(video_device, &buffer, length);

		if (ACPI_FAILURE(status) || !buffer ||
		    buffer->type != ACPI_TYPE_BUFFER) {
			length = 128;
			status = acpi_video_device_EDID(video_device, &buffer,
							length);
			if (ACPI_FAILURE(status) || !buffer ||
			    buffer->type != ACPI_TYPE_BUFFER) {
				continue;
			}
		}

		*edid = buffer->buffer.pointer;
		return length;
	}

	return -ENODEV;
}
EXPORT_SYMBOL(acpi_video_get_edid);

static int
acpi_video_bus_get_devices(struct acpi_video_bus *video,
			   struct acpi_device *device)
{
	/*
	 * There are systems where video module known to work fine regardless
	 * of broken _DOD and ignoring returned value here doesn't cause
	 * any issues later.
	 */
	acpi_video_device_enumerate(video);

	return acpi_dev_for_each_child(device, acpi_video_bus_get_one_device, video);
}

/* acpi_video interface */

/*
 * Win8 requires setting bit2 of _DOS to let firmware know it shouldn't
 * perform any automatic brightness change on receiving a notification.
 */
static int acpi_video_bus_start_devices(struct acpi_video_bus *video)
{
	return acpi_video_bus_DOS(video, 0,
				  acpi_osi_is_win8() ? 1 : 0);
}

static int acpi_video_bus_stop_devices(struct acpi_video_bus *video)
{
	return acpi_video_bus_DOS(video, 0,
				  acpi_osi_is_win8() ? 0 : 1);
}

static void acpi_video_bus_notify(acpi_handle handle, u32 event, void *data)
{
	struct acpi_device *device = data;
	struct acpi_video_bus *video = acpi_driver_data(device);
	struct input_dev *input;
	int keycode = 0;

	if (!video || !video->input)
		return;

	input = video->input;

	switch (event) {
	case ACPI_VIDEO_NOTIFY_SWITCH:	/* User requested a switch,
					 * most likely via hotkey. */
		keycode = KEY_SWITCHVIDEOMODE;
		break;

	case ACPI_VIDEO_NOTIFY_PROBE:	/* User plugged in or removed a video
					 * connector. */
		acpi_video_device_enumerate(video);
		acpi_video_device_rebind(video);
		keycode = KEY_SWITCHVIDEOMODE;
		break;

	case ACPI_VIDEO_NOTIFY_CYCLE:	/* Cycle Display output hotkey pressed. */
		keycode = KEY_SWITCHVIDEOMODE;
		break;
	case ACPI_VIDEO_NOTIFY_NEXT_OUTPUT:	/* Next Display output hotkey pressed. */
		keycode = KEY_VIDEO_NEXT;
		break;
	case ACPI_VIDEO_NOTIFY_PREV_OUTPUT:	/* previous Display output hotkey pressed. */
		keycode = KEY_VIDEO_PREV;
		break;

	default:
		acpi_handle_debug(device->handle, "Unsupported event [0x%x]\n",
				  event);
		break;
	}

	if (acpi_notifier_call_chain(device, event, 0))
		/* Something vetoed the keypress. */
		keycode = 0;

	if (keycode && (report_key_events & REPORT_OUTPUT_KEY_EVENTS)) {
		input_report_key(input, keycode, 1);
		input_sync(input);
		input_report_key(input, keycode, 0);
		input_sync(input);
	}
}

static void brightness_switch_event(struct acpi_video_device *video_device,
				    u32 event)
{
	if (!brightness_switch_enabled)
		return;

	video_device->switch_brightness_event = event;
	schedule_delayed_work(&video_device->switch_brightness_work, HZ / 10);
}

static void acpi_video_device_notify(acpi_handle handle, u32 event, void *data)
{
	struct acpi_video_device *video_device = data;
	struct acpi_device *device = NULL;
	struct acpi_video_bus *bus;
	struct input_dev *input;
	int keycode = 0;

	if (!video_device)
		return;

	device = video_device->dev;
	bus = video_device->video;
	input = bus->input;

	if (hw_changes_brightness > 0) {
		if (video_device->backlight)
			backlight_force_update(video_device->backlight,
					       BACKLIGHT_UPDATE_HOTKEY);
		acpi_notifier_call_chain(device, event, 0);
		return;
	}

	switch (event) {
	case ACPI_VIDEO_NOTIFY_CYCLE_BRIGHTNESS:	/* Cycle brightness */
		brightness_switch_event(video_device, event);
		keycode = KEY_BRIGHTNESS_CYCLE;
		break;
	case ACPI_VIDEO_NOTIFY_INC_BRIGHTNESS:	/* Increase brightness */
		brightness_switch_event(video_device, event);
		keycode = KEY_BRIGHTNESSUP;
		break;
	case ACPI_VIDEO_NOTIFY_DEC_BRIGHTNESS:	/* Decrease brightness */
		brightness_switch_event(video_device, event);
		keycode = KEY_BRIGHTNESSDOWN;
		break;
	case ACPI_VIDEO_NOTIFY_ZERO_BRIGHTNESS:	/* zero brightness */
		brightness_switch_event(video_device, event);
		keycode = KEY_BRIGHTNESS_ZERO;
		break;
	case ACPI_VIDEO_NOTIFY_DISPLAY_OFF:	/* display device off */
		brightness_switch_event(video_device, event);
		keycode = KEY_DISPLAY_OFF;
		break;
	default:
		acpi_handle_debug(handle, "Unsupported event [0x%x]\n", event);
		break;
	}

	if (keycode)
		may_report_brightness_keys = true;

	acpi_notifier_call_chain(device, event, 0);

	if (keycode && (report_key_events & REPORT_BRIGHTNESS_KEY_EVENTS)) {
		input_report_key(input, keycode, 1);
		input_sync(input);
		input_report_key(input, keycode, 0);
		input_sync(input);
	}
}

static int acpi_video_resume(struct notifier_block *nb,
				unsigned long val, void *ign)
{
	struct acpi_video_bus *video;
	struct acpi_video_device *video_device;
	int i;

	switch (val) {
	case PM_POST_HIBERNATION:
	case PM_POST_SUSPEND:
	case PM_POST_RESTORE:
		video = container_of(nb, struct acpi_video_bus, pm_nb);

		dev_info(&video->device->dev, "Restoring backlight state\n");

		for (i = 0; i < video->attached_count; i++) {
			video_device = video->attached_array[i].bind_info;
			if (video_device && video_device->brightness)
				acpi_video_device_lcd_set_level(video_device,
						video_device->brightness->curr);
		}

		return NOTIFY_OK;
	}
	return NOTIFY_DONE;
}

static acpi_status
acpi_video_bus_match(acpi_handle handle, u32 level, void *context,
			void **return_value)
{
	struct acpi_device *device = context;
	struct acpi_device *sibling;

	if (handle == device->handle)
		return AE_CTRL_TERMINATE;

	sibling = acpi_fetch_acpi_dev(handle);
	if (!sibling)
		return AE_OK;

	if (!strcmp(acpi_device_name(sibling), ACPI_VIDEO_BUS_NAME))
			return AE_ALREADY_EXISTS;

	return AE_OK;
}

static void acpi_video_dev_register_backlight(struct acpi_video_device *device)
{
	struct backlight_properties props;
	struct pci_dev *pdev;
	acpi_handle acpi_parent;
	struct device *parent = NULL;
	int result;
	static int count;
	char *name;

	result = acpi_video_init_brightness(device);
	if (result)
		return;

	name = kasprintf(GFP_KERNEL, "acpi_video%d", count);
	if (!name)
		return;
	count++;

	if (ACPI_SUCCESS(acpi_get_parent(device->dev->handle, &acpi_parent))) {
		pdev = acpi_get_pci_dev(acpi_parent);
		if (pdev) {
			parent = &pdev->dev;
			pci_dev_put(pdev);
		}
	}

	memset(&props, 0, sizeof(struct backlight_properties));
	props.type = BACKLIGHT_FIRMWARE;
	props.max_brightness =
		device->brightness->count - ACPI_VIDEO_FIRST_LEVEL - 1;
	device->backlight = backlight_device_register(name,
						      parent,
						      device,
						      &acpi_backlight_ops,
						      &props);
	kfree(name);
	if (IS_ERR(device->backlight)) {
		device->backlight = NULL;
		return;
	}

	/*
	 * Save current brightness level in case we have to restore it
	 * before acpi_video_device_lcd_set_level() is called next time.
	 */
	device->backlight->props.brightness =
			acpi_video_get_brightness(device->backlight);

	device->cooling_dev = thermal_cooling_device_register("LCD", device,
							      &video_cooling_ops);
	if (IS_ERR(device->cooling_dev)) {
		/*
		 * Set cooling_dev to NULL so we don't crash trying to free it.
		 * Also, why the hell we are returning early and not attempt to
		 * register video output if cooling device registration failed?
		 * -- dtor
		 */
		device->cooling_dev = NULL;
		return;
	}

	dev_info(&device->dev->dev, "registered as cooling_device%d\n",
		 device->cooling_dev->id);
	result = sysfs_create_link(&device->dev->dev.kobj,
			&device->cooling_dev->device.kobj,
			"thermal_cooling");
	if (result)
		pr_info("sysfs link creation failed\n");

	result = sysfs_create_link(&device->cooling_dev->device.kobj,
			&device->dev->dev.kobj, "device");
	if (result)
		pr_info("Reverse sysfs link creation failed\n");
}

static void acpi_video_run_bcl_for_osi(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev;
	union acpi_object *levels;

	mutex_lock(&video->device_list_lock);
	list_for_each_entry(dev, &video->video_device_list, entry) {
		if (!acpi_video_device_lcd_query_levels(dev->dev->handle, &levels))
			kfree(levels);
	}
	mutex_unlock(&video->device_list_lock);
}

static bool acpi_video_should_register_backlight(struct acpi_video_device *dev)
{
	/*
	 * Do not create backlight device for video output
	 * device that is not in the enumerated list.
	 */
	if (!acpi_video_device_in_dod(dev)) {
		dev_dbg(&dev->dev->dev, "not in _DOD list, ignore\n");
		return false;
	}

	if (only_lcd)
		return dev->flags.lcd;
	return true;
}

static int acpi_video_bus_register_backlight(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev;

	if (video->backlight_registered)
		return 0;

	if (acpi_video_get_backlight_type() != acpi_backlight_video)
		return 0;

	mutex_lock(&video->device_list_lock);
	list_for_each_entry(dev, &video->video_device_list, entry) {
		if (acpi_video_should_register_backlight(dev))
			acpi_video_dev_register_backlight(dev);
	}
	mutex_unlock(&video->device_list_lock);

	video->backlight_registered = true;

	video->pm_nb.notifier_call = acpi_video_resume;
	video->pm_nb.priority = 0;
	return register_pm_notifier(&video->pm_nb);
}

static void acpi_video_dev_unregister_backlight(struct acpi_video_device *device)
{
	if (device->backlight) {
		backlight_device_unregister(device->backlight);
		device->backlight = NULL;
	}
	if (device->brightness) {
		kfree(device->brightness->levels);
		kfree(device->brightness);
		device->brightness = NULL;
	}
	if (device->cooling_dev) {
		sysfs_remove_link(&device->dev->dev.kobj, "thermal_cooling");
		sysfs_remove_link(&device->cooling_dev->device.kobj, "device");
		thermal_cooling_device_unregister(device->cooling_dev);
		device->cooling_dev = NULL;
	}
}

static int acpi_video_bus_unregister_backlight(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev;
	int error;

	if (!video->backlight_registered)
		return 0;

	error = unregister_pm_notifier(&video->pm_nb);

	mutex_lock(&video->device_list_lock);
	list_for_each_entry(dev, &video->video_device_list, entry)
		acpi_video_dev_unregister_backlight(dev);
	mutex_unlock(&video->device_list_lock);

	video->backlight_registered = false;

	return error;
}

static void acpi_video_dev_add_notify_handler(struct acpi_video_device *device)
{
	acpi_status status;
	struct acpi_device *adev = device->dev;

	status = acpi_install_notify_handler(adev->handle, ACPI_DEVICE_NOTIFY,
					     acpi_video_device_notify, device);
	if (ACPI_FAILURE(status))
		dev_err(&adev->dev, "Error installing notify handler\n");
	else
		device->flags.notify = 1;
}

static int acpi_video_bus_add_notify_handler(struct acpi_video_bus *video)
{
	struct input_dev *input;
	struct acpi_video_device *dev;
	int error;

	video->input = input = input_allocate_device();
	if (!input) {
		error = -ENOMEM;
		goto out;
	}

	error = acpi_video_bus_start_devices(video);
	if (error)
		goto err_free_input;

	snprintf(video->phys, sizeof(video->phys),
			"%s/video/input0", acpi_device_hid(video->device));

	input->name = acpi_device_name(video->device);
	input->phys = video->phys;
	input->id.bustype = BUS_HOST;
	input->id.product = 0x06;
	input->dev.parent = &video->device->dev;
	input->evbit[0] = BIT(EV_KEY);
	set_bit(KEY_SWITCHVIDEOMODE, input->keybit);
	set_bit(KEY_VIDEO_NEXT, input->keybit);
	set_bit(KEY_VIDEO_PREV, input->keybit);
	set_bit(KEY_BRIGHTNESS_CYCLE, input->keybit);
	set_bit(KEY_BRIGHTNESSUP, input->keybit);
	set_bit(KEY_BRIGHTNESSDOWN, input->keybit);
	set_bit(KEY_BRIGHTNESS_ZERO, input->keybit);
	set_bit(KEY_DISPLAY_OFF, input->keybit);

	error = input_register_device(input);
	if (error)
		goto err_stop_dev;

	mutex_lock(&video->device_list_lock);
	list_for_each_entry(dev, &video->video_device_list, entry)
		acpi_video_dev_add_notify_handler(dev);
	mutex_unlock(&video->device_list_lock);

	return 0;

err_stop_dev:
	acpi_video_bus_stop_devices(video);
err_free_input:
	input_free_device(input);
	video->input = NULL;
out:
	return error;
}

static void acpi_video_dev_remove_notify_handler(struct acpi_video_device *dev)
{
	if (dev->flags.notify) {
		acpi_remove_notify_handler(dev->dev->handle, ACPI_DEVICE_NOTIFY,
					   acpi_video_device_notify);
		dev->flags.notify = 0;
	}
}

static void acpi_video_bus_remove_notify_handler(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev;

	mutex_lock(&video->device_list_lock);
	list_for_each_entry(dev, &video->video_device_list, entry)
		acpi_video_dev_remove_notify_handler(dev);
	mutex_unlock(&video->device_list_lock);

	acpi_video_bus_stop_devices(video);
	input_unregister_device(video->input);
	video->input = NULL;
}

static int acpi_video_bus_put_devices(struct acpi_video_bus *video)
{
	struct acpi_video_device *dev, *next;

	mutex_lock(&video->device_list_lock);
	list_for_each_entry_safe(dev, next, &video->video_device_list, entry) {
		list_del(&dev->entry);
		kfree(dev);
	}
	mutex_unlock(&video->device_list_lock);

	return 0;
}

static int instance;

static int acpi_video_bus_add(struct acpi_device *device)
{
	struct acpi_video_bus *video;
	bool auto_detect;
	int error;
	acpi_status status;

	status = acpi_walk_namespace(ACPI_TYPE_DEVICE,
				acpi_dev_parent(device)->handle, 1,
				acpi_video_bus_match, NULL,
				device, NULL);
	if (status == AE_ALREADY_EXISTS) {
		pr_info(FW_BUG
			"Duplicate ACPI video bus devices for the"
			" same VGA controller, please try module "
			"parameter \"video.allow_duplicates=1\""
			"if the current driver doesn't work.\n");
		if (!allow_duplicates)
			return -ENODEV;
	}

	video = kzalloc(sizeof(struct acpi_video_bus), GFP_KERNEL);
	if (!video)
		return -ENOMEM;

	/* a hack to fix the duplicate name "VID" problem on T61 */
	if (!strcmp(device->pnp.bus_id, "VID")) {
		if (instance)
			device->pnp.bus_id[3] = '0' + instance;
		instance++;
	}
	/* a hack to fix the duplicate name "VGA" problem on Pa 3553 */
	if (!strcmp(device->pnp.bus_id, "VGA")) {
		if (instance)
			device->pnp.bus_id[3] = '0' + instance;
		instance++;
	}

	video->device = device;
	strcpy(acpi_device_name(device), ACPI_VIDEO_BUS_NAME);
	strcpy(acpi_device_class(device), ACPI_VIDEO_CLASS);
	device->driver_data = video;

	acpi_video_bus_find_cap(video);
	error = acpi_video_bus_check(video);
	if (error)
		goto err_free_video;

	mutex_init(&video->device_list_lock);
	INIT_LIST_HEAD(&video->video_device_list);

	error = acpi_video_bus_get_devices(video, device);
	if (error)
		goto err_put_video;

	/*
	 * HP ZBook Fury 16 G10 requires ACPI video's child devices have _PS0
	 * evaluated to have functional panel brightness control.
	 */
	acpi_device_fix_up_power_children(device);

	pr_info("%s [%s] (multi-head: %s  rom: %s  post: %s)\n",
	       ACPI_VIDEO_DEVICE_NAME, acpi_device_bid(device),
	       video->flags.multihead ? "yes" : "no",
	       video->flags.rom ? "yes" : "no",
	       video->flags.post ? "yes" : "no");
	mutex_lock(&video_list_lock);
	list_add_tail(&video->entry, &video_bus_head);
	mutex_unlock(&video_list_lock);

	/*
	 * If backlight-type auto-detection is used then a native backlight may
	 * show up later and this may change the result from video to native.
	 * Therefor normally the userspace visible /sys/class/backlight device
	 * gets registered separately by the GPU driver calling
	 * acpi_video_register_backlight() when an internal panel is detected.
	 * Register the backlight now when not using auto-detection, so that
	 * when the kernel cmdline or DMI-quirks are used the backlight will
	 * get registered even if acpi_video_register_backlight() is not called.
	 */
	acpi_video_run_bcl_for_osi(video);
	if (__acpi_video_get_backlight_type(false, &auto_detect) == acpi_backlight_video &&
	    !auto_detect)
		acpi_video_bus_register_backlight(video);

	error = acpi_video_bus_add_notify_handler(video);
	if (error)
		goto err_del;

	error = acpi_dev_install_notify_handler(device, ACPI_DEVICE_NOTIFY,
						acpi_video_bus_notify, device);
	if (error)
		goto err_remove;

	return 0;

err_remove:
	acpi_video_bus_remove_notify_handler(video);
err_del:
	mutex_lock(&video_list_lock);
	list_del(&video->entry);
	mutex_unlock(&video_list_lock);
	acpi_video_bus_unregister_backlight(video);
err_put_video:
	acpi_video_bus_put_devices(video);
	kfree(video->attached_array);
err_free_video:
	kfree(video);
	device->driver_data = NULL;

	return error;
}

static void acpi_video_bus_remove(struct acpi_device *device)
{
	struct acpi_video_bus *video = NULL;


	if (!device || !acpi_driver_data(device))
		return;

	video = acpi_driver_data(device);

	acpi_dev_remove_notify_handler(device, ACPI_DEVICE_NOTIFY,
				       acpi_video_bus_notify);

	mutex_lock(&video_list_lock);
	list_del(&video->entry);
	mutex_unlock(&video_list_lock);

	acpi_video_bus_remove_notify_handler(video);
	acpi_video_bus_unregister_backlight(video);
	acpi_video_bus_put_devices(video);

	kfree(video->attached_array);
	kfree(video);
}

static int __init is_i740(struct pci_dev *dev)
{
	if (dev->device == 0x00D1)
		return 1;
	if (dev->device == 0x7000)
		return 1;
	return 0;
}

static int __init intel_opregion_present(void)
{
	int opregion = 0;
	struct pci_dev *dev = NULL;
	u32 address;

	for_each_pci_dev(dev) {
		if ((dev->class >> 8) != PCI_CLASS_DISPLAY_VGA)
			continue;
		if (dev->vendor != PCI_VENDOR_ID_INTEL)
			continue;
		/* We don't want to poke around undefined i740 registers */
		if (is_i740(dev))
			continue;
		pci_read_config_dword(dev, 0xfc, &address);
		if (!address)
			continue;
		opregion = 1;
	}
	return opregion;
}

/* Check if the chassis-type indicates there is no builtin LCD panel */
static bool dmi_is_desktop(void)
{
	const char *chassis_type;
	unsigned long type;

	chassis_type = dmi_get_system_info(DMI_CHASSIS_TYPE);
	if (!chassis_type)
		return false;

	if (kstrtoul(chassis_type, 10, &type) != 0)
		return false;

	switch (type) {
	case 0x03: /* Desktop */
	case 0x04: /* Low Profile Desktop */
	case 0x05: /* Pizza Box */
	case 0x06: /* Mini Tower */
	case 0x07: /* Tower */
	case 0x10: /* Lunch Box */
	case 0x11: /* Main Server Chassis */
		return true;
	}

	return false;
}

/*
 * We're seeing a lot of bogus backlight interfaces on newer machines
 * without a LCD such as desktops, servers and HDMI sticks. Checking the
 * lcd flag fixes this, enable this by default on any machines which are:
 * 1.  Win8 ready (where we also prefer the native backlight driver, so
 *     normally the acpi_video code should not register there anyways); *and*
 * 2.1 Report a desktop/server DMI chassis-type, or
 * 2.2 Are an ACPI-reduced-hardware platform (and thus won't use the EC for
       backlight control)
 */
static bool should_check_lcd_flag(void)
{
	if (!acpi_osi_is_win8())
		return false;

	if (dmi_is_desktop())
		return true;

	if (acpi_reduced_hardware())
		return true;

	return false;
}

int acpi_video_register(void)
{
	int ret = 0;

	mutex_lock(&register_count_mutex);
	if (register_count) {
		/*
		 * if the function of acpi_video_register is already called,
		 * don't register the acpi_video_bus again and return no error.
		 */
		goto leave;
	}

	if (only_lcd == -1)
		only_lcd = should_check_lcd_flag();

	dmi_check_system(video_dmi_table);

	ret = acpi_bus_register_driver(&acpi_video_bus);
	if (ret)
		goto leave;

	/*
	 * When the acpi_video_bus is loaded successfully, increase
	 * the counter reference.
	 */
	register_count = 1;

leave:
	mutex_unlock(&register_count_mutex);
	return ret;
}
EXPORT_SYMBOL(acpi_video_register);

void acpi_video_unregister(void)
{
	mutex_lock(&register_count_mutex);
	if (register_count) {
		acpi_bus_unregister_driver(&acpi_video_bus);
		register_count = 0;
		may_report_brightness_keys = false;
	}
	mutex_unlock(&register_count_mutex);
}
EXPORT_SYMBOL(acpi_video_unregister);

void acpi_video_register_backlight(void)
{
	struct acpi_video_bus *video;

	mutex_lock(&video_list_lock);
	list_for_each_entry(video, &video_bus_head, entry)
		acpi_video_bus_register_backlight(video);
	mutex_unlock(&video_list_lock);
}
EXPORT_SYMBOL(acpi_video_register_backlight);

bool acpi_video_handles_brightness_key_presses(void)
{
	return may_report_brightness_keys &&
	       (report_key_events & REPORT_BRIGHTNESS_KEY_EVENTS);
}
EXPORT_SYMBOL(acpi_video_handles_brightness_key_presses);

/*
 * This is kind of nasty. Hardware using Intel chipsets may require
 * the video opregion code to be run first in order to initialise
 * state before any ACPI video calls are made. To handle this we defer
 * registration of the video class until the opregion code has run.
 */

static int __init acpi_video_init(void)
{
	/*
	 * Let the module load even if ACPI is disabled (e.g. due to
	 * a broken BIOS) so that i915.ko can still be loaded on such
	 * old systems without an AcpiOpRegion.
	 *
	 * acpi_video_register() will report -ENODEV later as well due
	 * to acpi_disabled when i915.ko tries to register itself afterwards.
	 */
	if (acpi_disabled)
		return 0;

	if (intel_opregion_present())
		return 0;

	return acpi_video_register();
}

static void __exit acpi_video_exit(void)
{
	acpi_video_unregister();
}

module_init(acpi_video_init);
module_exit(acpi_video_exit);