[Bug 214899] ideapad-laptop: platform backlight device not working

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=214899

--- Comment #5 from Hans de Goede (jwrdegoede@fedoraproject.org) ---
Ah, ok so you indeed have "acpi_backlight=vendor" on the kernel commandline,
please don't do that, the old Ideapad specific backlight interface enabled by
that is only for very old laptop models.

Where as your laptop is very new! If you omit this, then you should only have
the intel_backlight under /sys/class/backlight and brightness control to e.g.
the slider in the GNOME system (top right) menu should work.

The brightness-keys directly changing the brightness is something from the same
era as the Ideapad specific backlight interface. Now a days almost without
exception the brightness keys will simply generate key-press events which are
processed by userspace to actually change the brightness. This allows userspace
to apply various policies to the brightness setting, for e.g. interaction with
auto-brightness control on devices with an ambient-light-sensor (ALS).

Almost all "integrated" desktop environments like GNOME, KDE, XFCE, MATE, etc.
will automatically do the right thing with the brightness-key events. If you
are however using e.g. i3 as window-manager then you will need to script this
yourself, there are plenty of examples how to do this.

###

So as said if you omit "acpi_backlight=vendor" on the kernel commandline, you
should only get the intel_backlight in /sys/class/backlight, which you have
already indicated works as it should.

All that remains then is to check that key-press events are properly generated
and if they are then this is "not a kernel bug". Please install evemu or evtest
and then run (as root) evemu-record or evtest and test for each input-device if
it perhaps sends brightness key-press events when pressing the brightness
hotkeys.

The following devices are a good starting point to test:
"AT Translated Set 2 keyboard"
"Video Bus"

But if neither of those works then please test them all 1 by 1. Note it is
possible that the "AT Translated Set 2 keyboard" generates only EV_MSC events
or the wrong EV_KEY codes for the brightness keys (so not
KEY_BRIGHTNESS[DOWN|UP]). In this case we need to add a mapping for your laptop
to fix this.

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