[Intel-gfx] [PATCH 1/2] drm/i915: Ensure the engine is idle before manually changing HWS

[Chris Wilson]

During reset_all_global_seqno() on seqno rollover, we have to update the
HWS. This causes all in flight requests to be completed, so first we
wait. However, we were only waiting for the requests themselves to be
completed and clearing out the waiter rbtrees - what I had missed was
the extra reference in execlists->port[]. Since commit fe9ae7a3bfdb
("drm/i915/execlists: Detect an out-of-order context switch") we can
detect when the request is retired before the context switch interrupt
is completed. The impact should be neglible outside of debugging.

Testcase: igt/gem_exec_whisper
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_request.c |  3 +++
 drivers/gpu/drm/i915/intel_engine_cs.c  | 31 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.h |  2 ++
 3 files changed, 36 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index c2cee9674cb0..b36a7644e055 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -196,6 +196,9 @@ static int reset_all_global_seqno(struct drm_i915_private *i915, u32 seqno)
 	for_each_engine(engine, i915, id) {
 		struct intel_timeline *tl = &timeline->engine[id];
 
+		if (wait_for(intel_engine_is_idle(engine), 50))
+			return -EBUSY;
+
 		if (!i915_seqno_passed(seqno, tl->seqno)) {
 			/* spin until threads are complete */
 			while (intel_breadcrumbs_busy(engine))
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index c58339b22f6a..53d65dc0c9fb 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -1071,6 +1071,37 @@ int intel_ring_workarounds_emit(struct drm_i915_gem_request *req)
 	return 0;
 }
 
+/**
+ * intel_engine_is_idle() - Report if the engine has finished process all work
+ * @engine: the intel_engine_cs
+ *
+ * Return true if there are no requests pending, nothing left to be submitted
+ * to hardware, and that the engine is idle.
+ */
+bool intel_engine_is_idle(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+
+	/* Any inflight/incomplete requests? */
+	if (!i915_seqno_passed(intel_engine_get_seqno(engine),
+			       intel_engine_last_submit(engine)))
+		return false;
+
+	/* Interrupt/tasklet pending? */
+	if (test_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted))
+		return false;
+
+	/* Both ports drained, no more ELSP submission? */
+	if (engine->execlist_port[0].request)
+		return false;
+
+	/* Ring stopped? */
+	if (INTEL_GEN(dev_priv) > 2 && !(I915_READ_MODE(engine) & MODE_IDLE))
+		return false;
+
+	return true;
+}
+
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
 #include "selftests/mock_engine.c"
 #endif
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 3dd6eee4a08b..38580765bfd6 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -664,4 +664,6 @@ static inline u32 *gen8_emit_pipe_control(u32 *batch, u32 flags, u32 offset)
 	return batch + 6;
 }
 
+bool intel_engine_is_idle(struct intel_engine_cs *engine);
+
 #endif /* _INTEL_RINGBUFFER_H_ */
-- 
2.11.0