drm/i915: Reduce breadcrumb lock coverage for intel_engine_enable_signaling()

Since intel_engine_enable_signaling() is now only called via
fence_enable_sw_signaling(), we can rely on it to provide serialisation
and run-once for us and so make ourselves slightly simpler.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-2-git-send-email-chris@chris-wilson.co.uk
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469530913-17180-1-git-send-email-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index d893ccd..9086744 100644 (file)
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -480,19 +480,15 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
        struct rb_node *parent, **p;
        bool first, wakeup;
 
-       if (unlikely(READ_ONCE(request->signaling.wait.tsk)))
-               return;
-
-       spin_lock(&b->lock);
-       if (unlikely(request->signaling.wait.tsk)) {
-               wakeup = false;
-               goto unlock;
-       }
+       /* locked by fence_enable_sw_signaling() */
+       assert_spin_locked(&request->lock);
 
        request->signaling.wait.tsk = b->signaler;
        request->signaling.wait.seqno = request->fence.seqno;
        i915_gem_request_get(request);
 
+       spin_lock(&b->lock);
+
        /* First add ourselves into the list of waiters, but register our
         * bottom-half as the signaller thread. As per usual, only the oldest
         * waiter (not just signaller) is tasked as the bottom-half waking
@@ -525,7 +521,6 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
        if (first)
                smp_store_mb(b->first_signal, request);
 
-unlock:
        spin_unlock(&b->lock);
 
        if (wakeup)