Re: [PATCH] drm/i915: Enable full PPGTT on gen7

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Sep 09, 2014 at 12:57:11PM +0100, Chris Wilson wrote:
> On Fri, Sep 05, 2014 at 02:13:16PM +0100, Michel Thierry wrote:
> > Use full PPGTT as the default option in gen7.
> > Note that aliasing PPGTT is the default option for gen8 (see HAS_PPGTT).
> > 
> > This may well come back to bite me later.
> 
> Indeed. So something I spotted was that bspec mentions that the per-ring
> PDE registers (RING_PP_DIR_DCLV and RING_PP_DIR_BASE) are stored in the
> logical context and so the registers are restored along with the
> context. If this is correct what happens when we switch logical contexts
> on RCS whilst we have active work on BCS etc? Does this mean that we
> have to serialise context switches across rings, or is my reading of the
> bspec false?

How does rcs PP_DIR_* affect bcs? Also IIRC that stuff is part of
the execlist context which isn't saved/restored unless execlists
are actually enabled. IIRC when I tried it, snb did reserve the
space for that stuff in the context image but didn't save/restore
it, but ivb+ didn't even reserve the space.

-- 
Ville Syrjälä
Intel OTC