I put a fresh installation of Debian Wheezy (Testing) on my T60 a couple
of weeks ago (long story) using XFCE desktop as the setup. I've noted,
with some annoyance, that when I change the screen brightness with the
Fn-Home/End keys that occasionally a graphical brightness icon appears
and when it does, the screen is dimmed or brightened in multiple steps.
The T60 has eight brightness levels and when this icon appears it cuts
it to about 4 levels.

Looking at /sys/class/backlight/acpi_video0/actual_brightness confirms
that the step will drop from 7 to 4 to 1 to 0 and then increase from 0
to 3 to 6 to 7. I would like some pointers on what tool/package is
generating the OSD icon and how I can kill it or tell it to use a step
size of 1. Oddly, I've had times when the OSD does not appear and I get
1 step per up/down key event.

- Nate >>

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Something in Sid changed recently to only provide 5 different brightness
settings with my X220. It's slightly annoying but I've decided to live
with it for the moment than to investigate what happened. Also running XFCE.

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Rubin
rubin@starset.net

On Mon, 20 Feb 2012, Nate Bargmann wrote:
> I put a fresh installation of Debian Wheezy (Testing) on my T60 a couple
> of weeks ago (long story) using XFCE desktop as the setup. I've noted,

Disable acpi video and disable thinkpad-acpi brightness control. This will
make sure no idiotic fluff in userspace will be able to screw with your
brightness control, unless it does it through X.org (which may or may not
control brightness, depends on the thinkpad model, and I don't recall
whether the T60 has EC-based brightness control or GPU-based brightness
control).

You can actually ask thinkpad-acpi to rat out the PIDs of processes messing
with brightness values [through thinkpad-acpi], check the documentation.

> with some annoyance, that when I change the screen brightness with the
> Fn-Home/End keys that occasionally a graphical brightness icon appears
> and when it does, the screen is dimmed or brightened in multiple steps.
> The T60 has eight brightness levels and when this icon appears it cuts
> it to about 4 levels.

This typically means broken crap that reacts to brightness *change* events
as if they were keypresses. Thinkpad-acpi doesn't issue those events by
default exactly for that reason, but some distros insist in breaking things.
IMMV. I have no idea what exactly happens when ACPI video is active, but it
is likely that it can be subject to the same problem. You can even get it
broken three times over, by forcing both thinkpad-acpi AND acpi-video to
issue the events, and react to both events by messing with the display
brightness.

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them all and in the darkness grind them. In the Land of Redmond
where the shadows lie." -- The Silicon Valley Tarot
Henrique Holschuh


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* On 2012 21 Feb 09:04 -0600, Henrique de Moraes Holschuh wrote:

> You can actually ask thinkpad-acpi to rat out the PIDs of processes messing
> with brightness values [through thinkpad-acpi], check the documentation.

I managed to do that by reloading the module as per the docs:

$ sudo modprobe thinkpad_acpi debug=0x8000

This allows debugging of PIDs. However, on this Debian system I finally
found the output in /var/log/auth.log! Huh? Whatever. I guess it uses
policytkit to handle the event.

What I found is:

Executing command [USER=root] [TTY=unknown] [CWD=/] [COMMAND=/usr/sb
in/xfpm-power-backlight-helper --set-brightness 3]

Which led to Debian bug report 627336:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=627336

Which, in turn, leads to this XFCE report:

https://bugzilla.xfce.org/show_bug.cgi?id=7541

Comments 13 and 15 describe how to disable xfpm from handling the
backlight. I used the following commands:

$ xfconf-query -c xfce4-power-manager -n -t bool -p
/xfce4-power-manager/change-brightness-on-key-events -s false

$ xfconf-query -c xfce4-power-manager -n -t bool -p
/xfce4-power-manager/show-brightness-popup -s false

I can report that the eight brightness levels are restored by the first
command and the OSD is disabled by the second.

I do recall that GNOME had the same issue and probably requires a
similar "fix".

- Nate >>

--

"The optimist proclaims that we live in the best of all
possible worlds. The pessimist fears this is true."

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On Tue, Feb 21, 2012 at 10:39:00AM -0600, Nate Bargmann wrote:
> I do recall that GNOME had the same issue and probably requires a
> similar "fix".

I can confirm. In a GNOME Shell session in Ubuntu 11.10 the brightness
goes from 15 down to 12 then down to 9 when I press Fn-End twice.

Bug: https://bugs.launchpad.net/ubuntu/+source/gnome-power-manager/+bug/527157

Upstream bug: https://bugzilla.gnome.org/show_bug.cgi?id=601410

The bug seems to be stuck in limbo

Marius Gedminas
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