Re: [Gnewsense-dev] Brightness changes spontaneously

[Mark H Weaver]

On Fri, Dec 25, 2009 at 04:31:27PM -0500, Richard Stallman wrote:
> I have an external battery connected.
> I reduce the brightness to conserve power.
> Every so often the system spontaneously changes to
> full brightness.

This bug was reported in 2006 and fixed upstream in April 2008, but
the version of gnome-power-manager we are using (from debian lenny) is
too old to include the fix.

  https://bugzilla.gnome.org/show_bug.cgi?id=335673

I backported the fix to the version in lenny and metad.  I've attached
a patch to this email, compiled it for mipsel/loongson, and put the
new source and binary packages into:

  fencepost.gnu.org:~mhw/gpm-metad1/

> For each of the distinct states it knows about, it should remember
> what brightness the user ast chose in that state.  When it leaves
> a state, it should store the current brightness as the last brightness
> for that state.  When it enters a state, it should set the brightness
> to the value stored for that state.  This way, no user-specified brightness
> change will ever be countermanded.  Instead, user-specified brightnesses
> will be swapped in and out.

Note that they considered this kind of scheme, but decided against it.
The problem is that the ambient light level is a better predictor of
desired brightness than the ac-power-state.  For example, if you were
in a bright environment the last time you used battery power, and now
are in a dark environment, unplugging the AC power would *brighten*
the backlight.

They opted for a scheme which remembers a "master" brightness level,
and optionally dims by a certain relative amount when switching to
battery power.

Ideally, it should probably *learn* the relationship between
desired-brightness-on-ac and desired-brightness-on-battery by watching
how the user adjusts the brightness shortly after ac-power-state
changes.

Note also that the backlight adjustment logic has gone through a great
deal of evolution since the version we are currently using.  We are
using version 2.20, and the last release is 2.30.  So far I've only
backported a single small fix from April 2008, but it might be
worthwhile to consider a more extensive backporting effort.

     Mark

gnome-power-manager-2.22.1-backlight-fix.diff
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