i915: black screen after boot on 915GM (Linux >= 3.4-rc1)

[Krzysztof Mazur]

Hi,

The commit 3f2dc5ac05714711fc14f2bf0ee5e42d5c08c581 (drm/i915: Fix 915GM
self-refresh enable/disable) causes strange regression on the HP Compaq
nc6120. During and after boot to framebuffer console with just LVDS
the screen is black (backlight on, but black). Starting a X server fixes
the problem. Connecting an external VGA monitor also fixes the problem.

Reverting this commit fixes the problem at least up to Linux 3.14.0-rc6.

I'm still using ACPI video problem workaround that effectively does:

 static int acpi_video_bus_start_devices(struct acpi_video_bus *video)
 {
- return acpi_video_bus_DOS(video, 0,
+ return acpi_video_bus_DOS(video, 3,
                            acpi_osi_is_win8() ? 1 : 0);
 }

in drivers/acpi/video.c.

I've added dmesgs from the last good commit and the bad commit at:
https://bugs.freedesktop.org/show_bug.cgi?id=76103

Thanks,
Krzysiek
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