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

Damien Lespiau
2014-08-27T07:51:35Z

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.

--
Damien
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