[Intel-gfx] [PATCH v4] drm/i915: Remove i915.enable_ppgtt override

[Chris Wilson]

Quoting Zhi Wang (2018-10-09 07:55:00)
> This is ideal and had been discussed in the beginning of upstream. 
> Mostly people didn't like this approach because it needs to modify i915 
> ppgtt code a lot and have to introduce a lot gvt-only code in i915 ppgtt.
> 
> The idea of the series of Joonas patch is to make PPGTT selection 
> per-platform. I guess that's the reason why he removed that check.
>  From his idea, there shouldn't be any platform which has execlist 
> support, but is still using aliasing PPGTT.
> 
> So it looks like there two approaches.
> 
> One is following the idea of this patch series: Platform with execlist 
> shouldn't touch aliasing PPGTT anymore, which needs GVT-g to create a 
> dummy PPGTT instance. (One dummy PPGTT instance for the architectural 
> design)
> 
> Another one is keeping the check as workaround like before.
> 
> I would like to choose a but b is also reasonable to me.

Creating a stub ppgtt to isolate the gvt context from the rest of the
system is very simple and ensures that (at least from our perspective)
the PDP always point to valid entries and not whatever lies at 0.
-Chris