drm/i915: Add a wakeref getter for iff the wakeref is already active

For use in the next patch, we want to acquire a wakeref without having
to wake the device up -- i.e. only acquire the engine wakeref if the
engine is already active.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190626154549.10066-1-chris@chris-wilson.co.uk
(cherry picked from commit de5147b8ce)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/gt/intel_engine_pm.h

@@ -7,12 +7,20 @@
 #ifndef INTEL_ENGINE_PM_H
 #define INTEL_ENGINE_PM_H
 
+#include "intel_engine_types.h"
+#include "intel_wakeref.h"
+
 struct drm_i915_private;
-struct intel_engine_cs;
 
 void intel_engine_pm_get(struct intel_engine_cs *engine);
 void intel_engine_pm_put(struct intel_engine_cs *engine);
 
+static inline bool
+intel_engine_pm_get_if_awake(struct intel_engine_cs *engine)
+{
+	return intel_wakeref_get_if_active(&engine->wakeref);
+}
+
 void intel_engine_park(struct intel_engine_cs *engine);
 
 void intel_engine_init__pm(struct intel_engine_cs *engine);

drivers/gpu/drm/i915/intel_wakeref.h

@@ -65,6 +65,21 @@ intel_wakeref_get(struct intel_runtime_pm *rpm,
 	return 0;
 }
 
+/**
+ * intel_wakeref_get_if_in_use: Acquire the wakeref
+ * @wf: the wakeref
+ *
+ * Acquire a hold on the wakeref, but only if the wakeref is already
+ * active.
+ *
+ * Returns: true if the wakeref was acquired, false otherwise.
+ */
+static inline bool
+intel_wakeref_get_if_active(struct intel_wakeref *wf)
+{
+	return atomic_inc_not_zero(&wf->count);
+}
+
 /**
  * intel_wakeref_put: Release the wakeref
  * @i915: the drm_i915_private device