drm: Document drm_atomic_*_get_property

Yes these are internal functions and not exported and we generally
don't document them. But for symmetry with the _set_property functions
(which are exported for the atomic helpers) I'd like to document them.
Upcoming vtable kerneldoc will reference both the set and get_property
functions.

v2: Suggestions from Thierry.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-17-git-send-email-daniel.vetter@ffwll.ch

Documentation/DocBook/gpu.tmpl

@@ -946,6 +946,7 @@ int max_width, max_height;</synopsis>
     <sect2>
       <title>Atomic Mode Setting Function Reference</title>
 !Edrivers/gpu/drm/drm_atomic.c
+!Idrivers/gpu/drm/drm_atomic.c
     </sect2>
     <sect2>
       <title>Frame Buffer Creation</title>

drivers/gpu/drm/drm_atomic.c

@@ -429,11 +429,20 @@ int drm_atomic_crtc_set_property(struct drm_crtc *crtc,
 }
 EXPORT_SYMBOL(drm_atomic_crtc_set_property);
 
-/*
+/**
+ * drm_atomic_crtc_get_property - get property value from CRTC state
+ * @crtc: the drm CRTC to set a property on
+ * @state: the state object to get the property value from
+ * @property: the property to set
+ * @val: return location for the property value
+ *
  * This function handles generic/core properties and calls out to
  * driver's ->atomic_get_property() for driver properties.  To ensure
  * consistent behavior you must call this function rather than the
  * driver hook directly.
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
  */
 static int
 drm_atomic_crtc_get_property(struct drm_crtc *crtc,
@@ -616,11 +625,20 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
 }
 EXPORT_SYMBOL(drm_atomic_plane_set_property);
 
-/*
+/**
+ * drm_atomic_plane_get_property - get property value from plane state
+ * @plane: the drm plane to set a property on
+ * @state: the state object to get the property value from
+ * @property: the property to set
+ * @val: return location for the property value
+ *
  * This function handles generic/core properties and calls out to
  * driver's ->atomic_get_property() for driver properties.  To ensure
  * consistent behavior you must call this function rather than the
  * driver hook directly.
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
  */
 static int
 drm_atomic_plane_get_property(struct drm_plane *plane,
@@ -872,11 +890,20 @@ int drm_atomic_connector_set_property(struct drm_connector *connector,
 }
 EXPORT_SYMBOL(drm_atomic_connector_set_property);
 
-/*
+/**
+ * drm_atomic_connector_get_property - get property value from connector state
+ * @connector: the drm connector to set a property on
+ * @state: the state object to get the property value from
+ * @property: the property to set
+ * @val: return location for the property value
+ *
  * This function handles generic/core properties and calls out to
  * driver's ->atomic_get_property() for driver properties.  To ensure
  * consistent behavior you must call this function rather than the
  * driver hook directly.
+ *
+ * RETURNS:
+ * Zero on success, error code on failure
  */
 static int
 drm_atomic_connector_get_property(struct drm_connector *connector,