[Intel-gfx] [bisect] regression in suspend with i915 on 82852/855GM

[Philipp Gesang]

Hi,

suspend/resume results in the backlight not coming back to life
on my X40 laptop with an “Display controller: Intel Corporation
82852/855GM Integrated Graphics Device”.

I bisected the issue. Apparently, commit
b0cd324faed23d10d66ba6ade66579c681feef6f introduced the problem.

    Author: Jani Nikula <jani.nikula at intel.com>
    Date:   Wed Nov 12 16:25:43 2014 +0200

        drm/i915: don't save/restore backlight hist ctl registers

I can confirm that suspend works as expected with a 4.1 kernel if
the lines to dump/undump the BLC_HIST_CTL register are
reintroduced; see the attached patch. (According to a web search,
the same issue seems to have arisen before in 2009, see [1].)

Let me know if you’d like me to run further tests on that
particular hardware.

Best,
Philipp

[1] http://lists.freedesktop.org/archives/intel-gfx/2009-October/004490.html


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