https://bugzilla.kernel.org/show_bug.cgi?id=215683
Bug ID: 215683
Summary: Display brightness goes to minimum on first AC power
plug event
Product: ACPI
Version: 2.5
Kernel Version: 5.17-rc6 (Mainline), 5.15.0-22 (Ubuntu)
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Video
Assignee: acpi_power-vi...@kernel-bugs.osdl.org
Reporter: w...@tuxedocomputers.com
Regression: No
After boot the first time AC power barrel blug is plugied in or out of a Clevo
NL50RU or NL50NU laptop, the display brightness goes to minimum. It can Still
be adjusted afterwards. It does not change again on subsequent AC power plug
events until next reboot.
It does not happen when acpi_backlight boot parameter is explicitly set to any
available value.
I noticed that the first call to acpi_video_get_backlight_type() happens by
acpi_video_bus_add()-> acpi_video_bus_register_backlight(). Here the default
value "acpi_backlight_video" is returned because
backlight_device_get_by_type(BACKLIGHT_RAW) returns a NULL.
Later during boot, acpi_video_get_backlight_type() is called again, this time
by acpi_video_backlight_notify_work(). But here it returns
"acpi_backlight_native", because backlight_device_get_by_type(BACKLIGHT_RAW)
now returns a pointer.
When setting the boot parameter explicitly this change in return value does not
happen, because then the boot parameter value is returned in both cases.
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