[Bug 86936] Facilitate override on minimum brightness level

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86936

--- Comment #4 from Aurabindo J <mail at aurabindo.in> ---
(In reply to Jani Nikula from comment #2)
> (In reply to Aurabindo J from comment #0)
> > Associated commit:
> > 
> > commit e1c412e75754ab7b7002f3e18a2652d999c40d4b
> > Author: Jani Nikula <jani.nikula at intel.com>
> > Date:   Wed Nov 5 14:46:31 2014 +0200
> > 
> >     drm/i915: safeguard against too high minimum brightness
> >     
> >     Never trust (your interpretation of) the VBT. Regression from
> >     
> >     commit 6dda730e55f412a6dfb181cae6784822ba463847
> >     Author: Jani Nikula <jani.nikula at intel.com>
> >     Date:   Tue Jun 24 18:27:40 2014 +0300
> >     
> >         drm/i915: respect the VBT minimum backlight brightness
> 
> The first commit ("drm/i915: respect the VBT minimum backlight brightness")
> is the real culprit in your case. It starts restricting the minimum
> brightness based on VBT. The VBT value is supposed to have been selected by
> the OEM to match the hardware requirements.

Yes, I noticed it right the first time itself, thats why I included info about
both the commits.

> 
> The second commit ("drm/i915: safeguard against too high minimum
> brightness") ensures the limit isn't "too high". It should *not* be
> effective in your case, where the minimum per VBT is (15/255)*max, i.e. you
> can't go below 5%.

my /sys/class/backlight/intel_backlight/max_brightness says 5273. So percentage
is calculated relative to this value ? The minimum level I can set is 64 after
the offending commit, which is obviously the arbitrary value hardcoded. It is
neither the 5%, which should have been ~264, nor 25%, which would be ~1319

If you meant 5% of *255* (and it is), which would be ~ 13, and it is not the
new minimum for me, rather 64. So where does 15 come into picture? Wild
rounding or anything else? And please clarify what "max" you meant.

Older one also showed proper actual_brightness. But latest kernel always gives
0. By older one, I meant the one without *both* of the referenced commit. I
didnt test it in between. Actually 3.10 (the one in centos 7). The newer on is
from arch (3.17)

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