"EDID checksum is invalid"

[Daniel Vetter]

On Wed, Jan 7, 2015 at 6:51 PM, Linus Torvalds
<torvalds at linux-foundation.org> wrote:
> On Tue, Jan 6, 2015 at 11:32 PM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>
>> Yeah if the edid probe fails userspace will get a hotplug and
>> autodisable the output. With a failsafe X session (just a dumb
>> terminal) we can avoid that to check that dpms on itself would work or
>> whether the edid probe fail here is just indicative of more trouble.
>> Also please boot with drm.debug=0xe, repro and grab dmesg, that might
>> shed some more light on what's failing.
>
> Here is an annotated attachment with the dpms off output witj drm.debug=0xe.
>
> It turns out the real failure case doesn't seem to be when the bad
> EDID happens. See my notes interspersed with the dmesg output.

Yeah some interesting stuff in there, but no idea why your screen is
ragequitting.
- The edid fail is indeed transiet. There's a bunch of hpd flip-flop
and some screaming (looks like crappy hw booting), but eventually the
kernel gets the full edid and mode list when you kick your hdmi
screen. But ofc the kernel doesn't do modeset since that's already
done. Have you tried whether a force full modeset with xrandr
--off/--auto fixes anything?
- There's nothing different for the deep-sleep dpms cycle that fails
to light up on the sink side - no errors from the modeset and no hpd
from the screen.
- But there is a difference on what userspace does: Somehow an
additionl very fast dpms off/on sneaks in when waking things up. Dunno
where that's from, but fickle screens tend to get upset by that. Maybe
try with the UXA backend in xorg.conf (which has a slightly different
dpms handling):

Section "Device"
        Identifier "igd"
        Driver "intel"
        Option "AccelMethod" "UXA"
EndSection

Otherwise I draw a blank. For the record do you know the old/new bios
versions, in case I can get hold of them and get a real changelog?
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch