[systemd-bugs] [Bug 66367] New: Provide handle for ACPI to change backlight brightness, similiar to other power-related ACPI events

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=66367

          Priority: medium
            Bug ID: 66367
          Assignee: systemd-bugs at lists.freedesktop.org
           Summary: Provide handle for ACPI to change backlight
                    brightness, similiar to other power-related ACPI
                    events
        QA Contact: systemd-bugs at lists.freedesktop.org
          Severity: enhancement
    Classification: Unclassified
                OS: Linux (All)
          Reporter: peter.weber at ttyhoney.com
          Hardware: All
            Status: NEW
           Version: unspecified
         Component: general
           Product: systemd

Hello!

Proposal:
Add a new handle named like "HandleBrightness" to Systemd and let it take care
of the brightness-events, which the kernel emits and signals to userspace.
Similiar to "HandleLidSwitch" or "HandleSuspendKey" and configureable via
"/etc/systemd/logind.conf". If a desktop-environment like GNOME, KDE or XFCE is
able to handle this itself, it should "inhibit" the handle.

I would avoid the postfix "Keys" because such an event could be trigged by
other things, like a light-sensor or something similiar.

Rationale:
Currently the handling of events triggered through the backlight-keys is weird
on GNU/Linux. If a key-press emits an event, the Linux-Kernel sends the event
to the userspace. At the same time, it is possible that the driver
ACPI_BACKLIGHT, inside the kernel, reacts on the event and changes the
backlight-brightness itself.

This is likely to change in future, instead the events will be only passed to
userspace.
http://lists.freedesktop.org/archives/intel-gfx/2013-March/026016.html
Patches:
https://patchwork.kernel.org/patch/2695411/
https://patchwork.kernel.org/patch/2695391/
https://patchwork.kernel.org/patch/2695401/

As a consequence the brightness-keys won't work on a terminal (TTY) or a plain
window-manager based on X11 or Wayland:
https://bugzilla.kernel.org/show_bug.cgi?id=51231#c107

Benefit:
This allows for changing the backlight-brigthness out-of-the-box. Especially on
a terminal (TTY), but also on any other kind of environmnet on top of X11 or
Wayland (i3wm, fluxbox, window-maker...$YOUR_SETUP_HERE).


Thank you
Peter

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