drm/i915: Kconfig for extra driver debugging

v2: Added a submenu based on an idea by Chris Wilson.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/Kconfig

@@ -56,3 +56,9 @@ config DRM_I915_USERPTR
 	  selected to enabled full userptr support.
 
 	  If in doubt, say "Y".
+
+menu "drm/i915 Debugging"
+depends on DRM_I915
+depends on EXPERT
+source drivers/gpu/drm/i915/Kconfig.debug
+endmenu

drivers/gpu/drm/i915/Kconfig.debug

+config DRM_I915_DEBUG
+        bool "Enable additional driver debugging"
+        depends on DRM_I915
+        default n
+        help
+          Choose this option to turn on extra driver debugging that may affect
+          performance but will catch some internal issues.
+
+          Recommended for driver developers only.
+
+          If in doubt, say "N".
+