[Intel-gfx] [PATCH 11/11] drm/i915: add HAS_ALIASING_PPGTT parameter for userspace

[Chris Wilson]

On Tue, 6 Dec 2011 09:39:39 -0800, Ben Widawsky <ben at bwidawsk.net> wrote:
> On Mon, Nov 28, 2011 at 10:24:55PM +0100, Daniel Vetter wrote:
> > On Sanybridge a few MI read/write commands only work when ppgtt is
> > enabled. Userspace therefore needs to be able to check whether ppgtt
> > is enabled. For added hilarity, you need to reset the "use global GTT"
> > bit on both snb/ivb when ppgtt is enabled, otherwise it won't work.
> > Despite what bspec says about automatically using ppgtt ...
> > 
> > Luckily PIPE_CONTROL (the only write cmd current userspace uses) is
> > not affected by all this, as tested by tests/gem_pipe_control_store_loop.
> 
> Since this is all SNB only, and we have no good benchmarks to show
> performance gains, can we not just enable this for IVB+?

Don't we have the same basic problem with IVB, that we need to adjust
the commands in the batchbuffer depending on whether HAS_ALIASING_PPGTT
is true? Or do you mean that we should just assume that IVB uses the
ppgtt and so kernel 3.3+, which will be around March...
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre