[Intel-gfx] [PATCH 01/19] drm/i915/execlists: Always clear ring_pause if we do not submit

[Chris Wilson]

In the unlikely case (thank you CI!), we may find ourselves wanting to
issue a preemption but having no runnable requests left. In this case,
we set the semaphore before computing the preemption and so must unset
it before forgetting (or else we leave the machine busywaiting until the
next request comes along and so likely hang).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index c8a0c9b32764..efccc31887de 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -233,13 +233,18 @@ static inline u32 intel_hws_preempt_address(struct intel_engine_cs *engine)
 static inline void
 ring_set_paused(const struct intel_engine_cs *engine, int state)
 {
+	u32 *sema = &engine->status_page.addr[I915_GEM_HWS_PREEMPT];
+
+	if (*sema == state)
+		return;
+
 	/*
 	 * We inspect HWS_PREEMPT with a semaphore inside
 	 * engine->emit_fini_breadcrumb. If the dword is true,
 	 * the ring is paused as the semaphore will busywait
 	 * until the dword is false.
 	 */
-	engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state;
+	*sema = state;
 	wmb();
 }
 
@@ -1243,6 +1248,8 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
 		*port = execlists_schedule_in(last, port - execlists->pending);
 		memset(port + 1, 0, (last_port - port) * sizeof(*port));
 		execlists_submit_ports(engine);
+	} else {
+		ring_set_paused(engine, 0);
 	}
 }
 
-- 
2.20.1