Screen goes black after switching from X to vt

[Martin Swift]

Dear Community,

A while back this issue cropped up and I'm now trying to solve it, and
would appreciate any insight that you might have.

When I'm running X and want to switch to a virtual terminal (e.g.
hitting ctr-alt-F1) the screen goes dark (though the backlight is
still on). I can still type (e.g. reboot the machine), I just can't
see anything.

The log file doesn't show any errors from the switch:

$ diff -u /var/log/Xorg.0.log*
[...]
+(II) AIGLX: Suspending AIGLX clients for VT switch
+(II) intel(0): xf86UnbindGARTMemory: unbind key 2
+(II) intel(0): xf86UnbindGARTMemory: unbind key 3
+(II) Video Bus: Close
+(II) UnloadModule: "evdev"
+(II) Power Button: Close
+(II) UnloadModule: "evdev"
+(II) UVC Camera (05ca:183a): Close
+(II) UnloadModule: "evdev"
+(II) AT Translated Set 2 keyboard: Close
+(II) UnloadModule: "evdev"
+(II) PS/2 Mouse: Close
+(II) UnloadModule: "evdev"
+(II) UnloadModule: "synaptics"
+(II) intel(0): [drm] removed 1 reserved context for kernel
+(II) intel(0): [drm] unmapping 8192 bytes of SAREA 0xfc8cc000 at 0xb7ad1000
+(II) intel(0): [drm] Closed DRM master.

Still, there are several warnings and errors earlier on, but I've not
progressed in finding anything of use online to fix these.

$ grep -E -e "^\([EW]{2}\)" /var/log/Xorg.0.log
(WW) intel(0): libpciaccess reported 0 rom size, guessing 64kB
(WW) intel(0): Register 0x61200 (PP_STATUS) changed from 0xc0000008 to 0xd0000009
(WW) intel(0): PP_STATUS before: on, ready, sequencing idle
(WW) intel(0): PP_STATUS after: on, ready, sequencing on
(WW) intel(0): Register 0x61110 (PORT_HOTPLUG_EN) changed from 0x06040220 to 0x06040020
(EE) intel(0): Failed to set tiling on front buffer: Invalid argument
(EE) intel(0): Failed to set tiling on back buffer: Invalid argument
(EE) intel(0): Failed to set tiling on depth buffer: Invalid argument
(WW) intel(0): PRB0_CTL (0x0001f001) indicates ring buffer enabled
(WW) intel(0): Existing errors found in hardware state.

Does anyone spot the cause or have pointers as to where to continue
looking?

Running:
* X.Org X Server 1.6.3.901 (1.6.4 RC 1)
* X.Org X11 7.4-r1
* Linux 2.6.30, Gentoo TuxOnIce-r6 patchset
Full log attached.

Cheers,
Martin
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