[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 #9 from Sonika <sonika.jindal at intel.com> ---
(In reply to ye.tian from comment #6)
> (In reply to Sonika from comment #2)
> > For me with kernel version 4.0.0-rc3, eDP is working fine.
> > 
> > The EDP low vswing table gets selected only when edp_vswing_preemph is set
> > in vbt.
> > For me, it works with both low vswing table as well as the dp translation
> > table with an edp1.3 panel.
> > 
> > Only thing I can suspect is that we are trying to use low vswing table for
> > some panel which is not able to handle those values.
> > Can you please see if this variable is set in vbt?
> > If it is set, please try to disable it and try.
> 
> I have no idea, could you tell me how to set this variable? where?

There should be one field in the eDP config in vbt VswingPreEmphasisValue.
Where it should be set to 0 for low vswing and 1 for default for the panel in
use:
    0 =  Low Power Swing setting(200 mV)
    1 =  Default Swing settings(400 mV)

If you have access to the code, you can try hardcoding
dev_priv->vbt.edp_low_vswing to false in parse_edp inside intel_bios.c to use
the default vswing values

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