[Intel-gfx] [PATCH 1/2] drm/i915: Assert the engine is idle before overwiting the HWS

[Chris Wilson]

When we update the global seqno (on the engine timeline), we modify HW
state (both registers and mapped pages). As we do this, we should be
sure that the HW is idle and we are not causing a conflict. The caller
is supposed to wait_for_idle before calling us to update the seqno, so
let's assert they have and the engine is indeed idle.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_request.c | 2 +-
 drivers/gpu/drm/i915/intel_engine_cs.c  | 4 ++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 6348353b91ec..2f8c5132b54e 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -214,8 +214,8 @@ static int reset_all_global_seqno(struct drm_i915_private *i915, u32 seqno)
 		}
 
 		/* Finally reset hw state */
-		tl->seqno = seqno;
 		intel_engine_init_global_seqno(engine, seqno);
+		tl->seqno = seqno;
 
 		list_for_each_entry(timeline, &i915->gt.timelines, link)
 			memset(timeline->engine[id].sync_seqno, 0,
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index 854e8e0c836b..92f871cf3265 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -223,6 +223,8 @@ void intel_engine_init_global_seqno(struct intel_engine_cs *engine, u32 seqno)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 
+	GEM_BUG_ON(!intel_engine_is_idle(engine));
+
 	/* Our semaphore implementation is strictly monotonic (i.e. we proceed
 	 * so long as the semaphore value in the register/page is greater
 	 * than the sync value), so whenever we reset the seqno,
@@ -260,6 +262,8 @@ void intel_engine_init_global_seqno(struct intel_engine_cs *engine, u32 seqno)
 	 * there are any waiters for that seqno.
 	 */
 	intel_engine_wakeup(engine);
+
+	GEM_BUG_ON(intel_engine_get_seqno(engine) != seqno);
 }
 
 static void intel_engine_init_timeline(struct intel_engine_cs *engine)
-- 
2.11.0