[Intel-gfx] patches for occlusion query fix on sandybridge

[Daniel Vetter]

On Tue, Dec 14, 2010 at 12:55:59PM +0800, Zhenyu Wang wrote:
> It appears Sandybridge PIPE_CONTROL write out buffer need
> to be set as cached, currently LLC cached, in order to read
> back correct counter. Otherwise I can always be possible to
> get corrupted 64-bit PS_DEPTH_COUNT from PIPE_CONTROL write.
> 
> So below patches try to add new flag during bo create with
> cacheable type, to be sure that GTT entry's cache bits would
> be setup for that.
> 
> This fixes occlusion query piglit test and mesa demos on my
> sandybridge. Note that below patches don't include necessary
> component version check changes.

General comment on the introduction of a new flag for bo creation:

If I'm not mistaken, all the query objects are relocated as read_domain =
I915_GEM_DOMAIN_INSTRUCTION, write_domain = I915_GEM_DOMAIN_INSTRUCTION,
i.e. we already have an api for userspace to tell us that a PIPE_CONTROL
command will write to this buffer. Why can't we use that one and remap
the bo with the correct caching flags on execbuf time (on gen6)?

I simply fear that introducing a hacky ad-hoc abi complicates matters when
we introduce real llc/mlc caching for general stuff. Especially since
there's seems to be an existing thing already available. I'm still
fighting the fallout from the incoherent multiple rings introduction and I
just don't want to repeat such a goof-up.

Yours, Daniel
-- 
Daniel Vetter
Mail: daniel at ffwll.ch
Mobile: +41 (0)79 365 57 48