[Bug 58151] kernel 3.2.45 regression in i915 driver for 00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=58151


Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
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             Status|NEW                         |NEEDINFO




--- Comment #5 from Jani Nikula <jani.nikula at intel.com>  2013-05-20 13:27:51 ---
(In reply to comment #4)
> (In reply to comment #3)
> > (In reply to comment #0)
> > > Using the same .config file on the same machine (Lenovo Thinkpad t400),
> > > compiling 3.2.44 kernel no problem, compiling 3.2.45 no backlight and no video.
> > > Disabling the modeseting by default on the .config and setting i915.modeset=0
> > > the backlight works, but, no framebuffer, and no control of backlight using Fn
> > > + Bright up/down.
> > 
> > This should be easy to bisect. See [1] for instructions. Just use the stable
> > tree [2] if you aren't already using that.
> > 
> > [1]
> > http://www.reactivated.net/weblog/archives/2006/01/using-git-bisect-to-find-buggy-kernel-patches/
> > [2] git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git
> 
> @Jani Nikula:
> 
> Can you fix it upstream please?. I already "fixed" it for myself (workaround
> i915.modeset=0 but no framebuffer and backlight control), but I'm asking you to
> fix it upstream please.

I don't know the root cause here. Fixing it would be easier if you did the
bisect, please. It means pinpointing the error introduced between v3.2.44 and
v3.2.45 to a single commit in the source.

You could also try reverting 
commit 19c42ce9869ff30f43a08fb774d08f35b92b5ff6
Author: Jani Nikula <jani.nikula at intel.com>
Date:   Fri Apr 12 15:18:38 2013 +0300

    drm/i915: ensure single initialization and cleanup of backlight device

which touches backlight code and see if that helps, but if it doesn't, it's
just useless back and forth when one should've just done the bisect. (Note that
I don't find anything obviously wrong with the commit.)

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