Bisected drm regression: 'xrandr --auto' does not turn on LVDS1

From: Carlos R. Mafra
Date: Mon Jan 24 2011 - 18:39:48 EST

Commit bf9dc102e28 ("drm: Set connector DPMS status to ON in
drm_crtc_helper_set_config") causes a regression in my laptop.

I always use the laptop connected to an external monitor,
so after booting I turn off the laptop panel with

xrandr --output LVDS1 --off

When I need to use the panel back, I turn it on with

xrandr --auto

That used to work in 2.6.36 and previous kernels, but no longer works
in 2.6.37 nor 2.6.38-rc2. The panel is turned off with the first command,
but 'xrandr --auto' does not turn it on again.

So I bisected the problem and arrived at the above commit (I did not
check whether reverting it from 2.6.37 or 2.6.38-rc2 also fixes the problem,

>From lspci -v:

00:02.0 VGA compatible controller: Intel Corporation Mobile GM965/GL960
Integrated Graphics Controller (rev 0c) (prog-if 00 [VGA controller])
Subsystem: Sony Corporation Device 9005
Flags: bus master, fast devsel, latency 0, IRQ 16
Memory at fc000000 (64-bit, non-prefetchable) [size=1M]
Memory at d0000000 (64-bit, prefetchable) [size=256M]
I/O ports at 1800 [size=8]
Expansion ROM at <unassigned> [disabled]
Capabilities: [90] MSI: Enable- Count=1/1 Maskable- 64bit-
Capabilities: [d0] Power Management version 3
Kernel driver in use: i915

The output of xrandr in 2.6.38-rc2 (which has the problem):

Pilar:/home/mafra/bin # xrandr
Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 8192 x 8192
LVDS1 connected 1280x800+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
1280x800 59.9*+
1024x768 85.0 75.0 70.1 60.0
832x624 74.6
800x600 85.1 72.2 75.0 60.3 56.2
640x480 85.0 72.8 75.0 59.9
720x400 85.0
640x400 85.1
640x350 85.1
VGA1 connected 1680x1050+0+0 (normal left inverted right x axis y axis) 473mm x 296mm
1680x1050 59.9*+ 60.0
1280x1024 75.0 60.0
1440x900 75.0 59.9
1280x960 60.0
1152x864 75.0
1024x768 75.1 60.0
832x624 74.6
800x600 75.0 60.3 56.2
640x480 75.0 60.0
720x400 70.1
TV1 unknown connection (normal left inverted right x axis y axis)
848x480 30.0 +
640x480 30.0 +
1024x768 30.0
800x600 30.0

I can gladly test patches and provide more info if needed.
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