[Intel-gfx] [PATCH] drm/i915: Enforce read order into the hardware status page csb

[Chris Wilson]

Quoting Chris Wilson (2018-04-12 14:57:42)
> Quoting Mika Kuoppala (2018-04-12 14:52:37)
> > Read ordering on cpu can be out of order and speculative.
> 
> If it didn't include a barrier to prevent compiler mispeculation. rmb()
> only applies to other CPU cores and not the GPU so this is entirely
> hocus.

To put it another way this is just imposing the cost of an uncached
mmio which the entire point of using HWSP in the first place is to
avoid.
-Chris