KDE backlight control - backlighthelper not running?

[Maciek Borzecki]

Problem solved, or at least I found a working workaround. Switching to
acpi_backlight=vendor makes things better. I can control brigthness by
using Fn keys, and the OSD appears when doing so.

Anyway the contents of backlight (avter using acpi_backlight=vendor)
$ ls -l /sys/class/backlight
total 0
lrwxrwxrwx. 1 root root 0 Mar  5 21:00 thinkpad_screen ->
../../devices/virtual/backlight/thinkpad_screen

Before the change, standard ACPI interface was there
(acpi_backlight=native, the default I guess), and it worked doing echo
[0-9] > brigthness.

Judging by kded/radeon code, it seems that powerdevil will use xrandr
brightness control when available (i.e. availability is reported by
querying Backlight property). Although setting 'Backlight' is not
supported by open source radeon driver, the check if the interface
exists succeeds. That's why it ended up trying to use xranrd which
does not work. The question is why the check even succeeded.

Funny though, xfce/gnome do not seem to ever use xrandr interface, and
always use /sys.

--
Maciek Borzecki



On Mon, Mar 5, 2012 at 1:03 PM, Lukáš Tinkl <ltinkl at redhat.com> wrote:
> Dne Ne 4. března 2012 13:58:36, Maciek Borzecki napsal(a):
>> I'm seeing an odd issue with KDE and screen backlight control. I'm
>> running Thinkpad T60, with KDE 4.7 (from updates) and unfortunately
>> the backlight control does not work. Pressing Fn+Home/Fn+End does not
>> seem to have any effect. I normally have to tweak hotkey mask to
>> something like 0xffffff in order to have the proper key events appear,
>> and it does work but only in Gnome and Xfce.
>> Before anyone suggests reinstalling bash, I've already done it
>> (otherwise it wouldn't work in Xfce).
>>
>> Looking at the logs:
>> - kded debugs:
>> kded(2495) PowerDevil::BackendLoader::loadBackend: Loading UPower backend...
>> kded(2495) PowerDevil::BackendLoader::loadBackend: Success!
>> kded(2495) KDEDPowerDevil::init: Backend loaded, loading core
>> kded(2495) PowerDevil::Core::loadCore: Core loaded, initializing backend
>> kded(2495) PowerDevilUPowerBackend::brightness: Screen brightness:  0
>> <---- why is current brightness 0?
>> kded(2495) PowerDevilUPowerBackend::init: current screen brightness:  0
>> kded(2495) PowerDevilUPowerBackend::init: Can suspend
>> kded(2495) PowerDevilUPowerBackend::init: Can hibernate
>> kded(2495) PowerDevil::Core::onBackendReady: Backend is ready, KDE
>> Power Management system initialized
>>
>> - messages - nothing about backlight helper being activated
>> - .xsession-errors - nothing related
>>
>> Since it does not work with 4.7 from updates, I updated to 4.8 from
>> kde48 repo. Unfortunately, with similar results.
>>
>> As a last resort I checked with KDE live spin, and amazingly,
>> backlight control works. So something between the current version of
>> packages and the one from live KDE spin, things got broken.
>>
>> Correct me if I'm wrong, but looking at the code, I see that in order
>> to control the backlight, there's a helper program
>> (/usr/libexec/kde4/backlighthelper) which starts through dbus
>> activation, and exposes brigthness, setbrigthness methods. I take that
>> once started the demon should remain running at lest for some time.
>> Now in KDE spin, that happens to be the case, I can clearly see
>> backlighthelper process listed in ps output (there are also logs in
>> messages, that activation of backlighthelper was successful).
>> However, right now, no such log is to be found, as if for some reason
>> backlight helper does not get started.
>>
>> Any ideas on how to proceed with debugging this?
>>
>> Thanks,
>> --
>> Maciek Borzecki
>> _______________________________________________
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>> kde at lists.fedoraproject.org
>> https://admin.fedoraproject.org/mailman/listinfo/kde
>> New to KDE4? - get help from http://userbase.kde.org
>
> Please post the result from "ls /sys/class/backlight/" on both systems
> --
> Lukáš Tinkl <ltinkl at redhat.com>
> Software Engineer - Base Operating Systems Brno
> KDE developer <lukas at kde.org>
> Red Hat Inc.                               http://cz.redhat.com
> _______________________________________________
> kde mailing list
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