[Intel-gfx] i915 / 3.15 intermittently boots into blank screeen

[Jan Niggemann]

Hi list,

you were very helpful to nail down the interrupt storm issue a year 
ago, I hope we can track this down, too.
I'm experiencing an issue with 3.15.5 on my Lenovo T400:
When my machine boots, I can see some of the boot messages flying by 
(quite fast because the machine has a SSD).
On a usual boot, the screen would go blank with the backlight off, come 
back on and other boot messages are visible in a different resolution. 
Finally the screen flickers once and shows the GDM login.
Since 3.15 (or 3.14, can't say for sure), the boot starts normally, but 
the first mode change doesn't occur, resulting in a black screen with 
backlight on. The system is entirely unresponsive and I can only press 
the power button until to switch it off.

This happens with my custom built kernel 3.15.5 but not with the Debian 
standard kernel 3.2.0 and IIRC neither with my custom built 3.14 
kernels.

Would a drm debug log help and if so, what kernel parameters should I 
use to generate it?

System environment
Lenovo T400, GM45 Express Chipset, custom-built kernel 3.15.5 on Debian 
7.5 /32bit, built-in LCD, issue happens 3 boots out of 4.

Best regards

Jan