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

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Date:	Tue, 29 Mar 2016 18:44:57 +0200
From:	Florian Zumbiehl <florz@...rz.de>
To:	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

Hi,

> 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.

Trying to collect that information actually solved the problem: fbcon
didn't actually get loaded during boot, only the graphics drivers, which
caused the screen to go blank, loading fbcon happened only when starting
the X server ... seems weird to me, but I guess there is some non-obvious
logic behind that, and in any case it seems to be a change in behaviour.
Well, thanks for the pointer anyway, I guess! ;-)

Now, while at it: I also have a bunch of WARN_ONs and ERRORs happening (the
former primarily when an Xv window disappears from the screen, it seems,
the latter primarily during boot), which don't seem to have any immediate
negative effects at the surface, like this:

| [   14.815467] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun
| [   14.815642] [drm:intel_set_cpu_fifo_underrun_reporting [i915]] *ERROR* pipe B underrun
| [   14.815806] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
| [   14.823686] [drm] initialized overlay support
| [   14.873165] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun

| [ 2520.457732] WARNING: CPU: 0 PID: 3193 at drivers/gpu/drm/i915/i915_gem.c:4508 i915_gem_free_object+0x277/0x280 [i915]()
| [ 2520.457736] WARN_ON(obj->frontbuffer_bits)

Also, I have occasional X server crashes (every few weeks or so) which
started with 4.1.9, I think (I had 3.11.0 before that), and I had some kind
of problem with Xv not working anymore until reboot with 4.1.9 which hasn't
happened with 4.4.5 yet ... do you think any of those would be worth
further investigation? If so, any suggestions as to how to split it all
into separate issues/how to go about it?

Regards, Florian