[Intel-gfx] [PATCH 02/10] drm/i915: fix FDI lane calculation

[Paulo Zanoni]

Hi

2012/11/20 Damien Lespiau <damien.lespiau at intel.com>:
>> -                * Account for spread spectrum to avoid
>> -                * oversubscribing the link. Max center spread
>> -                * is 2.5%; use 5% for safety's sake.
>> +                * The spec says:
>> +                * Number of lanes >= INT(dot clock * bytes per pixel / ls_clk)
>
> Right, so the real question is: "Is that ok to not get the spread rate
> (maximum of how much we derive from the requested frequency) into
> account?"

Well, the spec does not say we need to do this. Also, I tested this
patch on SNB and some modes that were moved from 3 to 2 lanes still
work.

>
> I believe it is, on average the frequency is what we set-up. Maybe
> Adam can shed more light on why he thought it was necessary?
>
> As a side note, the spec does not mention that at all.
>
> --
> Damien



-- 
Paulo Zanoni