[Bug 89554] [SKL Bisected] eDP can not be lighted up after entering kernel

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89554

--- Comment #36 from Sonika <sonika.jindal at intel.com> ---
As per the VBT VBIOS doc, default value in VBT should be 1 and not 0. If we are
setting it to 0 in VBT, it should be based upon the knowledge of the edp panel
VswingPreEmphasisValue:
    0 =  Low Power Swing setting(200 mV)
    1 =  Default Swing settings(400 mV)

I checked different versions of the GOP driver, and till 9.0.19, the default
setting was 1, while from 9.0.20 (which Wendy is using), it changed the value
to 0, which is not right.
Then in the release notes of this gop driver I see, that it was added to fix
one bug:
https://vthsd.fm.intel.com/hsd/pcgsw/default.aspx#bug/default.aspx?bug_id=5642130

>From the release notes:
[DCN][4132577] : [BUG] 5642130 : Change default VBT Setting to use Low Vswing
and Pre-emphasis for eDP display. : 9.0.1020

I strongly feel, we should not put a edp1.4 check there because its not
related.

For now, I would suggest to default it back to 1 in vbt and stitch a bios or
use one version older bios with gop 9.0.19.

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