[Intel-gfx] [PATCH v2 1/3] drm/i915: Fix 400 MHz FSB readout on elk

[Chris Wilson]

Quoting Ville Syrjala (2020-05-14 13:38:36)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Looks like elk redefines some of the CLKCFG FSB values to
> make room for 400 MHz FSB. The setting overlaps with one of
> the 266MHz settings (which is even documented in the ctg docs,
> and cofirmed to be correct on my ctg). So we limit the special
> case to elk only.
> 
> Though it might also be that we have some kind of desktop vs.
> mobile difference going on here as eg. both g35 and elk
> use 0x0 for the 266 MHz setting, vs. 0x6 used by ctg). The
> g35 doesn't let me select 400MHz for the FSB strap so can't
> confirm which way it would go here. But anyways as it seems
> only elk has the 400MHz option we shouldn't lose anything
> by limiting the special case to it alone.
> 
> My earlier experiments on this appear to have been nonsense as
> the comment I added claims that FSB strap of 400MHz results in
> a value of 0x4, but I've now retested it and I definitely get a
> value of 0x6 instead. So let's remove that bogus comment.
> 
> v2: s/_ELK/_ALT/ in the define in anticipation of a full
>     mobile vs. desktop CLKCFG split
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris