During igt_reset_nop_engine, it was observed that an unexpected failed
engine reset lead to us busywaiting on the stop-ring semaphore (set
during the reset preparations) on the first request afterwards. There was
no explicit MI_ARB_CHECK in this sequence as the presumption was that
the failed MI_SEMAPHORE_WAIT would itself act as an arbitration point.
It did not in this circumstance, so force it.
This patch is based on the assumption that the MI_SEMAPHORE_WAIT failure
to arbitrate is a rare Tigerlake bug, similar to the lite-restore vs
semaphore issues previously seen in the CS. The explicit MI_ARB_CHECK
should always ensure that there is at least one arbitration point in the
request before the MI_SEMAPHORE_WAIT to trigger the IDLE->ACTIVE event.
Upon processing that event, we will clear the stop-ring flag and release
the semaphore from its busywait.
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/gt/gen8_engine_cs.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
index 1ed9f572c8a4..8066b93e6dc4 100644
--- a/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
+++ b/drivers/gpu/drm/i915/gt/gen8_engine_cs.c
@@ -578,6 +578,7 @@ u32 *gen11_emit_fini_breadcrumb_rcs(struct i915_request *rq, u32 *cs)
static u32 *gen12_emit_preempt_busywait(struct i915_request *rq, u32 *cs)
{
+ *cs++ = MI_ARB_CHECK; /* trigger IDLE->ACTIVE first */
*cs++ = MI_SEMAPHORE_WAIT_TOKEN |
MI_SEMAPHORE_GLOBAL_GTT |
MI_SEMAPHORE_POLL |
@@ -586,7 +587,6 @@ static u32 *gen12_emit_preempt_busywait(struct i915_request *rq, u32 *cs)
*cs++ = preempt_address(rq->engine);
*cs++ = 0;
*cs++ = 0;
- *cs++ = MI_NOOP;
return cs;
}
--
2.20.1
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