[Bug 59841] [IVB cpu eDP] panel is broken due to 657445fe86 (eDP bpp clamping)

[bugzilla-daemon at bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=59841

--- Comment #179 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to jkp from comment #178)
> Are the DP_TRAINING_PATTERN_SET patches related to the reported bug or are
> they related to something else?

In *all* dmesgs here, and in the duplicate bugs, the clock recovery part of the
display port link training fails. Always. Regardless of UEFI vs. CSM,
regardless of 18 vs. 24 bpp, regardless of whether you get something on screen
eventually or not.

It just so happens the use of 24 bpp affects the link parameters so that the
channel equalization phase (which we try even though clock recovery failed)
succeeds by chance.

Fixing the link training should have priority, and "drm/i915/dp: do not write
DP_TRAINING_PATTERN_SET all the", now merged to drm-intel-nightly, does fix a
real issue with the link training.

"drm/i915/dp: prefer fast & narrow to wide & slow in DP per the spec" complies
with the display port spec.

> +1 to comment 164 quoted below
> 
> "Fabio Erculiani 2013-09-25 11:52:48 UTC
> 
> @intel.com:
> is there any hope to see the quirk merged while you work out a better (if
> any) solution? What could possibly go wrong, in the current situation the
> screen is dead anyway (I hardly believe that Asus will ever release a fixed
> firmware)."

The quirk hides the real issue (link training) under the carpet.

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