Fix TLB invalidate issues with Broadwell

i915 selftest hangcheck is causing the i915 driver timeouts, as reported by Intel CI bot:

http://gfx-ci.fi.intel.com/cibuglog-ng/issuefilterassoc/24297?query_key=42a999f48fa6ecce068bc8126c069be7c31153b4

When such test runs, the only output is:

	[   68.811639] i915: Performing live selftests with st_random_seed=0xe138eac7 st_timeout=500
	[   68.811792] i915: Running hangcheck
	[   68.811859] i915: Running intel_hangcheck_live_selftests/igt_hang_sanitycheck
	[   68.816910] i915 0000:00:02.0: [drm] Cannot find any crtc or sizes
	[   68.841597] i915: Running intel_hangcheck_live_selftests/igt_reset_nop
	[   69.346347] igt_reset_nop: 80 resets
	[   69.362695] i915: Running intel_hangcheck_live_selftests/igt_reset_nop_engine
	[   69.863559] igt_reset_nop_engine(rcs0): 709 resets
	[   70.364924] igt_reset_nop_engine(bcs0): 903 resets
	[   70.866005] igt_reset_nop_engine(vcs0): 659 resets
	[   71.367934] igt_reset_nop_engine(vcs1): 549 resets
	[   71.869259] igt_reset_nop_engine(vecs0): 553 resets
	[   71.882592] i915: Running intel_hangcheck_live_selftests/igt_reset_idle_engine
	[   72.383554] rcs0: Completed 16605 idle resets
	[   72.884599] bcs0: Completed 18641 idle resets
	[   73.385592] vcs0: Completed 17517 idle resets
	[   73.886658] vcs1: Completed 15474 idle resets
	[   74.387600] vecs0: Completed 17983 idle resets
	[   74.387667] i915: Running intel_hangcheck_live_selftests/igt_reset_active_engine
	[   74.889017] rcs0: Completed 747 active resets
	[   75.174240] intel_engine_reset(bcs0) failed, err:-110
	[   75.174301] bcs0: Completed 525 active resets

After that, the machine just silently hangs.

Bisecting the issue, the patch that introduced the regression is:

    7938d61591d3 ("drm/i915: Flush TLBs before releasing backing store")

Reverting it fix the issues, but introduce other problems, as TLB won't be invalidated anymore. So, instead, let's fix the root cause.

It turns that the TLB flush logic ends conflicting with i915 reset, which is called during selftest hangcheck. So, the TLB cache should be serialized together with i915 reset.

Tested on an Intel NUC5i7RYB with an i7-5557U Broadwell CPU.

v5:
- Added a missing SoB on patch 2.
- No other changes.

v4:
- No functional changes. All changes are at the patch descriptions:
- collected acked-by/reviewed-by;
- use the same e-mail on Author and SoB on patch 1.

v3:
- Removed the logic that would check if the engine is awake before doing TLB flush invalidation as backporting PM logic up to Kernel 4.x could be too painful. After getting this one merged, I'll submit a separate patch with the PM awake logic.

v2:

- Reduced to bare minimum fixes, as this shoud be backported deeply into stable.

Chris Wilson (2):
drm/i915/gt: Serialize GRDOM access between multiple engine resets drm/i915/gt: Serialize TLB invalidates with GT resets

 drivers/gpu/drm/i915/gt/intel_gt.c    | 15 ++++++++++-
 drivers/gpu/drm/i915/gt/intel_reset.c | 37 ++++++++++++++++++++-------
 2 files changed, 42 insertions(+), 10 deletions(-)

2.36.1