drm/i915: Replace nested subclassing with explicit subclasses

In the next patch, we will want a third distinct class of timeline that
may overlap with the current pair of client and engine timeline classes.
Rather than use the ad hoc markup of SINGLE_DEPTH_NESTING, initialise
the different timeline classes with an explicit subclass.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180706210710.16251-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem.c

@@ -3095,7 +3095,7 @@ static void engine_skip_context(struct i915_request *request)
 	GEM_BUG_ON(timeline == &engine->timeline);
 
 	spin_lock_irqsave(&engine->timeline.lock, flags);
-	spin_lock_nested(&timeline->lock, SINGLE_DEPTH_NESTING);
+	spin_lock(&timeline->lock);
 
 	list_for_each_entry_continue(request, &engine->timeline.requests, link)
 		if (request->gem_context == hung_ctx)

drivers/gpu/drm/i915/i915_request.c

@@ -503,7 +503,7 @@ static void move_to_timeline(struct i915_request *request,
 	GEM_BUG_ON(request->timeline == &request->engine->timeline);
 	lockdep_assert_held(&request->engine->timeline.lock);
 
-	spin_lock_nested(&request->timeline->lock, SINGLE_DEPTH_NESTING);
+	spin_lock(&request->timeline->lock);
 	list_move_tail(&request->link, &timeline->requests);
 	spin_unlock(&request->timeline->lock);
 }

drivers/gpu/drm/i915/i915_timeline.h

@@ -37,6 +37,8 @@ struct i915_timeline {
 	u32 seqno;
 
 	spinlock_t lock;
+#define TIMELINE_CLIENT 0 /* default subclass */
+#define TIMELINE_ENGINE 1
 
 	/**
 	 * List of breadcrumbs associated with GPU requests currently

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -483,6 +483,7 @@ static void intel_engine_init_execlist(struct intel_engine_cs *engine)
 void intel_engine_setup_common(struct intel_engine_cs *engine)
 {
 	i915_timeline_init(engine->i915, &engine->timeline, engine->name);
+	lockdep_set_subclass(&engine->timeline.lock, TIMELINE_ENGINE);
 
 	intel_engine_init_execlist(engine);
 	intel_engine_init_hangcheck(engine);

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -200,6 +200,8 @@ struct intel_engine_cs *mock_engine(struct drm_i915_private *i915,
 	engine->base.submit_request = mock_submit_request;
 
 	i915_timeline_init(i915, &engine->base.timeline, engine->base.name);
+	lockdep_set_subclass(&engine->base.timeline.lock, TIMELINE_ENGINE);
+
 	intel_engine_init_breadcrumbs(&engine->base);
 	engine->base.breadcrumbs.mock = true; /* prevent touching HW for irqs */