From 8db7933ee3d442627c716ee49a70fa3aef18640d Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 24 Jun 2019 10:20:09 +0100
Subject: drm/i915/execlists: Always clear ring_pause if we do not submit
Git-commit: 8db7933ee3d442627c716ee49a70fa3aef18640d
Patch-mainline: v5.4-rc1
References: bsc#1152489

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).

v2: Replace readback with only a wmb after asserting the semaphore

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190624092009.30189-1-chris@chris-wilson.co.uk
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/i915/gt/intel_lrc.c | 5 ++++-
 1 file changed, 4 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..28685ba91a2c 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -240,7 +240,8 @@ ring_set_paused(const struct intel_engine_cs *engine, int state)
 	 * until the dword is false.
 	 */
 	engine->status_page.addr[I915_GEM_HWS_PREEMPT] = state;
-	wmb();
+	if (state)
+		wmb();
 }
 
 static inline struct i915_priolist *to_priolist(struct rb_node *rb)
@@ -1243,6 +1244,8 @@ 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);
 	}
 }
 
-- 
2.28.0