[Bug 91393] [bdw edp] Screen Flickering

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91393

--- Comment #68 from Mika Kahola <mika.kahola at intel.com> ---
Created attachment 120893
  --> https://bugs.freedesktop.org/attachment.cgi?id=120893&action=edit
DP debugging

Tom, I would bother you again to provide some debugging info. From the dmesg
you sent it seems that you are experiencing a lot of hpd interrupts. When that
happens the driver checks if the DP channel equalization is still ok. On your
case, channel equalization is not ok yielding DP link to be retrained. Of
course, this causes flickering as the DP link is broken for some time. The
patch I'm proposing for debugging purposes applies on top of the latest
-nightly and on top of these previous patches 

https://patchwork.freedesktop.org/patch/69394/
https://patchwork.freedesktop.org/patch/69395/
https://patchwork.freedesktop.org/patch/69396/

The patch adds more verbose debug information on channel equalization and
limits the DP link retraining to 5. After 5 attempts to retrain the link you
probably end up having a non-flickering display or a black screen. Please,
report back with dmesg.

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