drm/i915: Local debug BUG_ON for intel_wakeref

Avoid pulling in i915_gem.h just so that we can use a conditional BUG_ON
for debugging.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621183801.23252-5-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
index 9cbb2eb..d45e786 100644
--- a/drivers/gpu/drm/i915/intel_wakeref.h
+++ b/drivers/gpu/drm/i915/intel_wakeref.h
@@ -13,6 +13,12 @@
 #include <linux/stackdepot.h>
 #include <linux/timer.h>
 
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG)
+#define INTEL_WAKEREF_BUG_ON(expr) BUG_ON(expr)
+#else
+#define INTEL_WAKEREF_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
+#endif
+
 struct intel_runtime_pm;
 
 typedef depot_stack_handle_t intel_wakeref_t;
@@ -86,6 +92,7 @@ intel_wakeref_put(struct intel_runtime_pm *rpm,
 		  struct intel_wakeref *wf,
 		  int (*fn)(struct intel_wakeref *wf))
 {
+	INTEL_WAKEREF_BUG_ON(atomic_read(&wf->count) <= 0);
 	if (atomic_dec_and_mutex_lock(&wf->count, &wf->mutex))
 		return __intel_wakeref_put_last(rpm, wf, fn);