[Bug 55311] Since 3.7.1-17.1 radeon has no backlight when using vgaswitcheroo (regression)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=55311

--- Comment #38 from Tom Wijsman <TomWij at gentoo.org> ---
Fix present in 3.10 for the Gentoo bug.

We discovered through a git bisect that a line intel_modeset_disable(dev); was
added to i915_drm_freeze in drivers/gpu/drm/i915/i915_drv.c which is called
when the user switches away from Intel; since the system in question is MUX-ed
the Radeon output is routed through (or near) the Intel card, therefore
disabling modesetting (CRTC) causes the Radeon output to not show.

We verified that removing the added line above resolves the issue. When I was
planning to file a bug about this I checked for the presence of that line in
the latest kernel releases; and apparently it isn't, to my surprise the commit
below appears to remove the line because disabling modesetting (CRTC) appears
to no longer be needed.

http://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=24576d23976746cb52e7700c4cadbf4bc1bc3472

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