[systemd-devel] systemd-backlight and backlight level 0

[Lennart Poettering]

On Wed, 05.03.14 09:46, Josh Triplett (josh at joshtriplett.org) wrote:

> systemd-backlight saves backlight levels on shutdown, and restores them
> on startup.  However, on some systems, backlight level 0 actually turns
> the backlight *off*; this can potentially make the system unusable.
> Complicating matters, on most systems, nothing pays attention to the
> brightness adjustment keys in text mode.
> 
> I'd suggest one or both of the following two changes, to avoid a painful
> failure mode:
> 
> - systemd-backlight should avoid saving/restoring a backlight level of
>   0, and have a minimum backlight level.  (Possibly overridable via
>   configuration, for people who *really* want to restore backlight level
>   0.)

To deal with situations like this there's systemd.restore_state=0 on the
kernel cmdline, see kernel-command-line(7).

I could be convinced to fix brightness level 0 to 1 when restoring. But
then again, I fear the next people will come then and say "1 is only
marginally better than 0, i want the minimum to be 16!"... Or even
others saying "Dude, I only got 3 brightness levels, and you took one
away from me...". So I am not enthusiastic about the idea...

> - Something ought to listen to the brightness keys (and perhaps other
>   hotkeys) in pure text mode.  systemd seems like a good place for such
>   a something to live.

That's definitely a job for the DE I am sure, so that can it do an OSD
and all the other stuff. We do power button handling in logind only
because what it does is relatively important and really close to the
system lifecycle... But brightness keys (or volume keys..) are not close
at all. I am really sure that that's for the DEs to handle, not us.

Lennart

-- 
Lennart Poettering, Red Hat