[Intel-gfx] External display pixelated after upgrade to kernel >= 4.11.0-rc1

[neil k]

Hey everyone,

I have a new Thinkpad with a Kaby Lake CPU and Intel HD Graphics 620.  I
had been using a 26" Vizio TV (1360x768) over HDMI as an external monitor
with no issues.  I upgraded to a 4.11 series kernel and now the TV is very
pixelated (see attached picture.)  I posted some logs/info on the kernel
bugzilla here <https://bugzilla.kernel.org/show_bug.cgi?id=196065>.  I had
to nuke that Fedora install, but I have attached dmesg logs from Xubuntu
booted with the drm.debug=0xe option.  Xubuntu logs are with the laptop
screen at 1600x900.

Here's what I've found so far in addition to the bugzilla post:

- TV still works if I use a USB-C to VGA adapter instead of HDMI.
- Still see the issue if I force HDMI-A-2 to use the EDID extracted from
VGA, which has no HD modelines
- I compiled a nightly kernel from
git://anongit.freedesktop.org/git/drm-intel a few days ago with no change
(see dmesg attachment)

Is this is a known issue, or does anyone have any ideas about what changed
in 4.11.0-rc1 that could have caused this?  I see a lot of changes for the
i915 driver were made in that kernel version.  If I can provide anything
else to help investigate, please let me know.

Thanks,
Neil
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