[Intel-gfx] [PATCH v6 0/6] Add Per-context WA using WA batch buffers

[Arun Siluvery]

>From Gen8+ we have some workarounds that are applied Per context and
they are applied using special batch buffers called as WA batch buffers.
HW executes them at specific stages during context save/restore.
The patches in this series adds this framework to i915.

I did some basic testing on BDW by running glmark2 and didn't see any issues.
These WA are mainly required when preemption is enabled.

[v1] http://lists.freedesktop.org/archives/intel-gfx/2015-February/060707.html
[v2] http://www.spinics.net/lists/intel-gfx/msg67804.html

[v3] In v2, two separate ring_buffer objects were used to load WA instructions
and they were part of every context which is not really required.
Chris suggested a better approach of adding a page to context itself and using
it for this purpose. Since GuC is also planning to do the same it can probably
be shared with GuC. But after discussions it is agreed to use an independent
page as GuC area might grow in future. Independent page also makes sense because
these WA are only initialized once and not changed afterwards so we can share
them across all contexts.

[v4] Changes in this revision,
In the previous version the size of batch buffers are fixed during
initialization which is not a good idea. This is corrected by updating the
functions that load WA to return the number of dwords written and caller
updates the size once all WA are initialized. The functions now also accept
offset field which allows us to have multiple batches so that required batch
can be selected based on a criteria. This is not a requirement at this point
but could be useful in future.

WaFlushCoherentL3CacheLinesAtContextSwitch implementation was incomplete which
is fixed and programming restrictions correctly applied.

http://www.spinics.net/lists/intel-gfx/msg68947.html

[v5] No major changes in this revision but switched to new revision as changes
affected all patches. Introduced macro to add commands which also checks for
page overflow. Moved code around to simplify, indentation fixes and other
improvements suggested by Chris.

Since we don't know the number of WA applied upfront, Chris suggested a two-pass
approach but that brings additional complexity which is not necessary.
Discussed with Chris and agreed upon on single page setup as simpler code wins
and also single page is sufficient for our requirement.

http://www.spinics.net/lists/intel-gfx/msg69176.html

[v6] Changes made to make the code easy to modify for future Gen. It is much
neater and contained now, big thanks to Chris Wilson for the review.
Since these changes affect all patches I am sending as a separate revision.

Please see the patches for more details.

Arun Siluvery (6):
  drm/i915/gen8: Add infrastructure to initialize WA batch buffers
  drm/i915/gen8: Re-order init pipe_control in lrc mode
  drm/i915/gen8: Add WaDisableCtxRestoreArbitration workaround
  drm/i915/gen8: Add WaFlushCoherentL3CacheLinesAtContextSwitch
    workaround
  drm/i915/gen8: Add WaClearSlmSpaceAtContextSwitch workaround
  drm/i915/gen8: Add WaRsRestoreWithPerCtxtBb workaround

 drivers/gpu/drm/i915/i915_reg.h         |  32 +++-
 drivers/gpu/drm/i915/intel_lrc.c        | 328 +++++++++++++++++++++++++++++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h |  21 ++
 3 files changed, 374 insertions(+), 7 deletions(-)

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2.3.0