[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 #19 from wendy.wang at intel.com ---
(In reply to Sonika from comment #9)
> (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

Hello, we read GOP driver's vbt info:   pre-emphasis was set to level-0 by
default, Voltage Swing was set to swing-0 by default.
Both the machines which installed older and newer panels flashed the same GOP
driver version.

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