From 49b20dbf7497597070b74e987d52274e8815cfed Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 12 Jan 2021 10:07:59 +0000 Subject: [PATCH] drm/i915/gt: Perform an arbitration check before busywaiting 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 Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20210112100759.32698-2-chris@chris-wilson.co.uk --- 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; }