[Intel-gfx] [PATCH v4] drm/i915: Be more careful to drop the GT wakeref

[Chris Wilson]

Since we can retire requests from multiple paths, we cannot assume that
i915_gem_retire_requests() is the sole path on which we can transition
to gt.active_requests == 0. A consequence of this is that we would skip
the function if we had already retired all the requests and not
scheduled the idle worker.

This is fallout from changing the routine from considering active_engines
(over which it was the only consumer) to active_requests.

v2: Move kicking the idle working to i915_gem_request_retire() otherwise
we could postpone the idle callback everytime we called retire_requests
even though we did no work.
v3: We only need to move the idle work kicking!

Fixes: 28176ef4cfa5 ("drm/i915: Reserve space in the global seqno during request allocation")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_gem_request.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index b9b5253cf3cd..ad6057dc495e 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -218,7 +218,12 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 	 */
 	list_del(&request->ring_link);
 	request->ring->last_retired_head = request->postfix;
-	request->i915->gt.active_requests--;
+	if (!--request->i915->gt.active_requests) {
+		GEM_BUG_ON(!request->i915->gt.awake);
+		mod_delayed_work(request->i915->wq,
+				 &request->i915->gt.idle_work,
+				 msecs_to_jiffies(100));
+	}
 
 	/* Walk through the active list, calling retire on each. This allows
 	 * objects to track their GPU activity and mark themselves as idle
@@ -763,6 +768,8 @@ static void i915_gem_mark_busy(const struct intel_engine_cs *engine)
 	if (dev_priv->gt.awake)
 		return;
 
+	GEM_BUG_ON(!dev_priv->gt.active_requests);
+
 	intel_runtime_pm_get_noresume(dev_priv);
 	dev_priv->gt.awake = true;
 
@@ -1150,9 +1157,4 @@ void i915_gem_retire_requests(struct drm_i915_private *dev_priv)
 
 	for_each_engine(engine, dev_priv, id)
 		engine_retire_requests(engine);
-
-	if (!dev_priv->gt.active_requests)
-		mod_delayed_work(dev_priv->wq,
-				 &dev_priv->gt.idle_work,
-				 msecs_to_jiffies(100));
 }
-- 
2.10.2