[PATCH] drm/i915: don't flush TLB on GEN8

[Mauro Carvalho Chehab <mchehab@kernel.org>]

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

	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.

The root cause is that the flush TLB logic is not working as
expected on GEN8.

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

This patch partially reverts the logic by skipping GEN8 from
the TLB cache flush.

Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Sushma Venkatesh Reddy <sushma.venkatesh.reddy@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org # Kernel 5.17 and upper

Fixes: 494c2c9b630e ("drm/i915: Flush TLBs before releasing backing store")
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
---

Patch resent, as the first version was using an old email. That's what happens
when writing patches on old test machines ;-)

 drivers/gpu/drm/i915/gt/intel_gt.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index 034182f85501..7965a77e5046 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -1191,10 +1191,10 @@ void intel_gt_invalidate_tlbs(struct intel_gt *gt)
 	if (GRAPHICS_VER(i915) == 12) {
 		regs = gen12_regs;
 		num = ARRAY_SIZE(gen12_regs);
-	} else if (GRAPHICS_VER(i915) >= 8 && GRAPHICS_VER(i915) <= 11) {
+	} else if (GRAPHICS_VER(i915) > 8 && GRAPHICS_VER(i915) <= 11) {
 		regs = gen8_regs;
 		num = ARRAY_SIZE(gen8_regs);
-	} else if (GRAPHICS_VER(i915) < 8) {
+	} else if (GRAPHICS_VER(i915) <= 8) {
 		return;
 	}
 
-- 
2.36.1