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

[Daniel Vetter]

On Thu, Jul 17, 2014 at 10:31:30PM +0200, Jan Niggemann wrote:
> 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?

Your box seems to die in the initial modeset, which is done with the
console_lock held. Which means any crashdumps in dmesg won't get out to
netconsole or anything else unfortunately.

I think the only way to move forward here is to double-check that 3.14
works and 3.15 is broken by recompiling with the same .config
(occasionally config changes cause regressions). And then do a full git
bisect to find the offending commit.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch