linux-kernel - Re: blank screen on boot with i915/DRM_FBDEV

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Date:	Tue, 29 Mar 2016 14:01:18 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Florian Zumbiehl <florz@...rz.de>
Cc:	intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel.vetter@...el.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>
Subject: Re: blank screen on boot with i915/DRM_FBDEV_EMULATION

On Sat, Mar 26, 2016 at 12:21:23PM +0100, Florian Zumbiehl wrote:
> Hi,
> 
> I just compiled a new kernel version 4.4.5, replacing a previous 4.1.9 for
> my thinkpad x40, which replaced CONFIG_DRM_I915_FBDEV with
> CONFIG_DRM_FBDEV_EMULATION--now, when the i915 and fbcon modules get loaded
> during boot, the screen goes blank (with backlight still on), which didn't
> happen with the old kernel.
> 
> The funny thing is that starting an X server makes text reappear on the
> console!? (And the X server also works just fine, as far as I can tell so
> far ...)
> 
> i915 is loaded with modeset=1 (I remember I had some problem without it
> with some earlier kernels, I don't really remember the details anymore
> ...).
> 
> Any hints what to try? Any further information that could be useful?

FBDEV_EMULATION vs. I915_FBDEV is probably a read herring, more likely is
that for some odd reason the very first modeset fails. Once X has
resurrect the screen, can you then switch to fbcon? Also please check in
/sys/class/vtconsole whether the fbdev driver is loaded and bound (check
the name and bind files). And make sure there's that dmesg still says it
initialized the "inteldrmfb" driver.

If that all indicates fbcon is running properly, then it's time to bisect
what exactly broke the initial modeset for your system.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch