Fixing the MATE backlight applet

SteveM

The Power Manager Brightness Applet in MATE is unable to talk to my laptop's backlight so I've been using /usr/bin/backlight to control it with keyboard shortcuts redirected to use it. I finally got around to looking under the hood and found that /usr/bin/backlight uses ioctl to directly control /dev/backlight/backlight0 whereas the MATE applet is currently using dbus-glib calls. There is also a PR in process to convert the applet to GDBus calls.

Is the best route to fix this to patch the MATE applet to use ioctl calls or is it there going to be something in dbus-glib or GDBus that can be patched instead to enable it to correctly control the backlight?

vimanuelt

In the meantime, you can try this workaround: xcrsz/display-control

SteveM

I'd rather not. I mentioned I am able to control backlight with /usr/bin/backlight and some keybindings so I'm not needing a stop gap. You suggested an 18M monster that is less convenient and uses xrandr to control the software brightness which leaves my backlight alone. This is a laptop, backlight power consumption matters.

I probably should have asked the FreeBSD people anyway.

vimanuelt

SteveM
Yes, they own the delivery of this solution. You can press them to complete it, as their previous work only covered 3 vendors.

SteveM

To start to answer my own question, the issue is not with dbus as mate-power-manager is simply using it for IPC and the underlying problem is that src/gpm-backlight-helper.c is written specifically for Linux. The FreeBSD package maintainer patched the file to simply return an error code that a backlight could not be found. So I believe that the correct fix is to modify src/gpm-backlight-helper.c to use ioctl