Re: [PATCH 1/7] drm: Renaming DP training vswing pre emph defines

[Thierry Reding <thierry.reding@gmail.com>]

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On Wed, Aug 27, 2014 at 08:51:35AM +0100, Damien Lespiau wrote:
> On Wed, Aug 27, 2014 at 08:47:54AM +0100, Damien Lespiau wrote:
> > > An alternative would be to provide a second set of defines for eDP 1.4
> > > where the name implies the meaning and then use them as appropriate.
> > 
> > We went through the idea as well and:
> > 
> > I actually think the nominal voltage swing and pre-emph values are quite
> > misleading. The hw is free to implement a wildly different set of voltage
> > swing/pre-emph values.
> > 
> > eDP 1.4 changes those nominal values as described in the cover letter,
> > but there again, the actual hw implementation can choose fairly
> > different values than the nominal ones.
> > 
> > Also, the DP 1.2 spec documents this field as (see address 103h):
> > 
> > TRAINING_LANE0_SET : Link Training Control_Lane0
> >   Bits 1:0 = VOLTAGE SWING SET
> >     00 –Voltage swing level 0
> >     01 –Voltage swing level 1
> >     10 –Voltage swing level 2
> >     11 –Voltage swing level 3
> > 
> > So, in that sense, we're closer to the latest spec with those LEVEL_X
> > defines.
> 
> I forgot to mention here that if we have separate defines for eDP 1.4,
> then we lose the possibility to share training code with big DP and eDP
> 1.3, not something desirable.

Yeah, I'd like to see the training sequences extracted into common
helpers.

Thierry

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