[Bug 105267] Screen goes blurry after getting hpd irq

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=105267

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      i915 platform|                            |CFL
      i915 features|                            |display/eDP

--- Comment #5 from Jani Nikula <jani.nikula at intel.com> ---
Seems to be a Coffeelake with a Cannonlake PCH. (Mysteriously the device info
is missing from the logs.)

I have no clue about the root cause yet, but what happens is that the eDP panel
signals short pulse hotplug. This indicates the panel requests a link status
check. We do this, and find the link status is in fact not good. To remedy, we
try to re-train the link. The link training succeeds. This is all according to
DP spec. From the logs, there is nothing out of the ordinary. But apparently
the link retraining leads to flickering.

The hotplug occurs at about 71 seconds into the boot. If this is typical, this
should give you enough time to do a modeset (disable/enable display, but don't
suspend/resume) before this happens due to the hotplug. Does this cause
flicker? Or only when the panel requests link status check?

The simple thing (for us) to do is double check the Coffeelake DDI buffer
translations and link training values, especially see if there have been any
recent updates to the specs.

Curiously the VBT refers to Skylake. I'm wondering where the VBT comes from and
whether it's been updated for the platform at hand.

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