Comment 34 for bug 505271

Using xorg-edgers (libdrm 2.4.17+git20100210.4f0f8717-0ubuntu0sarvatt, which contains commit 4f0f871730b76730ca58209181d16725b0c40184) seems to at least partially "fix" it:

- log in to gnome with compiz enabled
- close lid -> backlight turns off
- open lid -> backlight stays off
- switch vts: vt7 -> vt1 (backlight comes back on) -> vt7
- have a working desktop

I have rebooted 3 times to verify that this behavior is consistent, since it was also working this way in the past for some reason.

The reason I write "partially" is not because the backlight isn't being turned on again, but because I still get errors in both dmesg and Xorg.0.log:

[... close lid ...]
[ 35.941034] dell-wmi: Unknown key ffd0 pressed
[...]
[ 46.932531] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[ 46.932541] render error detected, EIR: 0x00000000
[ 46.932544] i915: Waking up sleeping processes
[ 46.932569] [drm:i915_wait_request] *ERROR* i915_wait_request returns -5 (awaiting 1568 at 1558)
[ 46.933227] [drm:i915_gem_execbuffer] *ERROR* Execbuf while wedged
[ 46.933340] [drm:i915_gem_execbuffer] *ERROR* Execbuf while wedged
[ 46.938810] [drm:i915_gem_execbuffer] *ERROR* Execbuf while wedged
[ 47.700027] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[ 47.700035] render error detected, EIR: 0x00000000
[ 47.700037] i915: Waking up sleeping processes
[ 47.700069] [drm:i915_wait_request] *ERROR* i915_wait_request returns -5 (awaiting 1569 at 1558)
[ 49.090027] [drm:i915_hangcheck_elapsed] *ERROR* Hangcheck timer elapsed... GPU hung
[ 49.090034] render error detected, EIR: 0x00000000
[ 49.090037] i915: Waking up sleeping processes
[ 49.090070] [drm:i915_wait_request] *ERROR* i915_wait_request returns -5 (awaiting 1571 at 1558)
[... open lid ...]
[ 49.175642] [drm] LVDS-8: set mode 1440x900 28
[ 49.500086] dell-wmi: Unknown key ffd1 pressed
[...]

and

[...]
(II) intel(0): Modeline "1440x900"x0.0 71.88 1440 1486 1556 1928 900 909 918 932 +hsync -vsync (37.3 kHz)
(EE) intel(0): Failed to submit batch buffer, expect rendering corruption or even a frozen display: Input/output error.
(EE) intel(0): Failed to submit batch buffer, expect rendering corruption or even a frozen display: Input/output error.
(WW) intel(0): i830_uxa_prepare_access: gtt bo map failed: Input/output error
[...]

The backlight-not-turning-back-on portion is indeed a separate bug (which Nicolò reported as #488328), it just also happens on lid-closing.

While I was investigating the backlight issue, I found http://bugzilla.kernel.org/show_bug.cgi?id=14997 which indicates that on kernel 2.6.32 not only the display is disabled, but the display is actually being disconnected (in order to save power). This means that X is running with "no attached outputs".
Could it be that, since the error messages seem to only appear when the lid is closed, those are actually a side-effect of X running with no attached outputs?