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linux/Documentation/ABI/stable/sysfs-class-backlight
Thomas Zimmermann a1cacb8a8e backlight: Add BACKLIGHT_POWER_ constants for power states
Duplicate FB_BLANK_ constants as BACKLIGHT_POWER__ constants in the
backlight header file. Allows backlight drivers to avoid including
the fbdev header file and removes a compile-time dependency between
the two subsystems.

The new BACKLIGHT_POWER_ constants have the same values as their
FB_BLANK_ counterparts. Hence UAPI and internal semantics do not
change. The backlight drivers can be converted one by one. Each
instance of FB_BLANK_UNBLANK becomes BACKLIGHT_POWER_ON, each of
FB_BLANK_POWERDOWN becomes BACKLIGHT_POWER_OFF, and FB_BLANK_NORMAL
becomes BACKLIGHT_POWER_REDUCED.

Backlight code or drivers do not use FB_BLANK_VSYNC_SUSPEND and
FB_BLANK_HSYNC_SUSPEND, so no new constants for these are being
added.

The semantics of FB_BLANK_NORMAL appear inconsistent. In fbdev,
NORMAL means display off with sync enabled. In backlight code,
this translates to turn the backlight off, but some drivers
interpret it as backlight on. So we keep the current code as is,
but mark BACKLIGHT_POWER_REDUCED as deprecated. Drivers should be
fixed and the constant removed. This affects ams369fg06 and a few
DRM panel drivers.

v2:
- rename BL_CORE_ power constants to BACKLIGHT_POWER_ (Sam)
- fix documentation

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20240624152033.25016-2-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>
2024-07-04 16:45:25 +01:00

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What: /sys/class/backlight/<backlight>/bl_power
Date: April 2005
KernelVersion: 2.6.12
Contact: Richard Purdie <rpurdie@rpsys.net>
Description:
Control BACKLIGHT power, values are compatible with
FB_BLANK_* from fb.h
- 0 (FB_BLANK_UNBLANK) : power on.
- 4 (FB_BLANK_POWERDOWN) : power off
Users: HAL
What: /sys/class/backlight/<backlight>/brightness
Date: April 2005
KernelVersion: 2.6.12
Contact: Richard Purdie <rpurdie@rpsys.net>
Description:
Control the brightness for this <backlight>. Values
are between 0 and max_brightness. This file will also
show the brightness level stored in the driver, which
may not be the actual brightness (see actual_brightness).
Users: HAL
What: /sys/class/backlight/<backlight>/actual_brightness
Date: March 2006
KernelVersion: 2.6.17
Contact: Richard Purdie <rpurdie@rpsys.net>
Description:
Show the actual brightness by querying the hardware.
Users: HAL
What: /sys/class/backlight/<backlight>/max_brightness
Date: April 2005
KernelVersion: 2.6.12
Contact: Richard Purdie <rpurdie@rpsys.net>
Description:
Maximum brightness for <backlight>.
Users: HAL
What: /sys/class/backlight/<backlight>/type
Date: September 2010
KernelVersion: 2.6.37
Contact: Matthew Garrett <mjg@redhat.com>
Description:
The type of interface controlled by <backlight>.
"firmware": The driver uses a standard firmware interface
"platform": The driver uses a platform-specific interface
"raw": The driver controls hardware registers directly
In the general case, when multiple backlight
interfaces are available for a single device, firmware
control should be preferred to platform control should
be preferred to raw control. Using a firmware
interface reduces the probability of confusion with
the hardware and the OS independently updating the
backlight state. Platform interfaces are mostly a
holdover from pre-standardisation of firmware
interfaces.