drm/i915: Enable i915_gem_wait_for_idle() without holding struct_mutex

The principal motivation for this was to try and eliminate the
struct_mutex from i915_gem_suspend - but we still need to hold the mutex
current for the i915_gem_context_lost(). (The issue there is that there
may be an indirect lockdep cycle between cpu_hotplug (i.e. suspend) and
struct_mutex via the stop_machine().) For the moment, enabling last
request tracking for the engine, allows us to do busyness checking and
waiting without requiring the struct_mutex - which is useful in its own
right.

As a side-effect of having a robust means for tracking engine busyness,
we can replace our other busyness heuristic, that of comparing against
the last submitted seqno. For paranoid reasons, we have a semi-ordered
check of that seqno inside the hangchecker, which we can now improve to
an ordered check of the engine's busyness (removing a locked xchg in the
process).

v2: Pass along "bool interruptible" as being unlocked we cannot rely on
i915->mm.interruptible being stable or even under our control.
v3: Replace check Ironlake i915_gpu_busy() with the common precalculated value

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-6-git-send-email-chris@chris-wilson.co.uk

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index f495969..e9b301a 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -166,6 +166,12 @@ void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
 	memset(&engine->hangcheck, 0, sizeof(engine->hangcheck));
 }
 
+static void intel_engine_init_requests(struct intel_engine_cs *engine)
+{
+	init_request_active(&engine->last_request, NULL);
+	INIT_LIST_HEAD(&engine->request_list);
+}
+
 /**
  * intel_engines_setup_common - setup engine state not requiring hw access
  * @engine: Engine to setup.
@@ -177,13 +183,13 @@ void intel_engine_init_hangcheck(struct intel_engine_cs *engine)
  */
 void intel_engine_setup_common(struct intel_engine_cs *engine)
 {
-	INIT_LIST_HEAD(&engine->request_list);
 	INIT_LIST_HEAD(&engine->buffers);
 	INIT_LIST_HEAD(&engine->execlist_queue);
 	spin_lock_init(&engine->execlist_lock);
 
 	engine->fence_context = fence_context_alloc(1);
 
+	intel_engine_init_requests(engine);
 	intel_engine_init_hangcheck(engine);
 	i915_gem_batch_pool_init(engine, &engine->batch_pool);
 }