[Mesa-dev] [PATCH 00/12] i965/gen7+: Implement fast color clears.

[Paul Berry]

This series implements fast color clears, a Gen7+ feature which
reduces memory bandwidth by deferring the memory writes involved in a
glClear() until the same memory is later touched during rendering.

>From a broad overview point of view, fast color clears work in a
similar way to HiZ: an auxiliary "MCS" buffer keeps track of which
parts of the buffer have been cleared but haven't yet had the
necessary memory writes performed.  Whenever a color buffer needs to
be accessed by the CPU, or by a part of the GPU that is not
fast-color-aware, we have to perform a "resolve operation" to force
any pending memory writes to occur.

This patch series adopts a slightly different strategy (compared to
HiZ) for making sure the resolves happen when needed.  Instead of
modifying each code path that might need to do a resolve so that it
does one if needed, we create an accessor function that does the
resolve if needed and then provides the caller with access to the
miptree's underlying memory region.  This lets us have a lot more
confidence that we didn't miss any code paths, which is important
since color buffers are accessed by a large number of code paths.  To
discourage future maintainers from trying to bypass the accessor
function, it is inline (so that overhead is negligible), and the field
it provides access to has been renamed to region_private.

Patch 01 ifdefs out some code so that it does not appear in the i915
(pre-Gen4) driver--this makes it easier to be confident that these
changes won't regress i915.  Patch 02 introduces the aforementioned
accessor function.  Patches 03-11 are the guts of the implementation,
and patch 12 enables the new feature.

No piglit regressions.  I have additional piglit tests which validate
specific important corner cases--I hope to get those out to the list
later this week.

[PATCH 01/12] intel: Conditionally compile mcs-related code for i965 only.
[PATCH 02/12] intel: Create intel_miptree_get_region() to prepare for fast color clear.
[PATCH 03/12] i965/gen7+: Create an enum for keeping track of fast color clear state.
[PATCH 04/12] i965/gen7+: Set up MCS in SURFACE_STATE whenever MCS is present.
[PATCH 05/12] i965/gen7+: Create helper functions for single-sample MCS buffers.
[PATCH 06/12] i965/gen7+: Implement fast color clear operation in BLORP.
[PATCH 07/12] i965/blorp: Expand clear class hierarchy to prepare for RT resolves.
[PATCH 08/12] i965/blorp: Write blorp code to do render target resolves.
[PATCH 09/12] i965/gen7+: Ensure that front/back buffers are fast-clear resolved.
[PATCH 10/12] i965/gen7+: Resolve color buffers when necessary.
[PATCH 11/12] i965/gen7+: Disable fast color clears on shared regions.
[PATCH 12/12] i965/gen7: Enable support for fast color clears.