device property: Add a note to the fwnode.h

Add a note to the fwnode.h that the header should not be used
directly in the leaf drivers, they all should use the higher
level APIs and the respective headers.

The purpose of this note is to give guidance to driver writers
to avoid repeating a common mistake.

Signed-off-by: Andy Shevchenko <[email protected]>
Reviewed-by: Sakari Ailus <[email protected]>
Reviewed-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Zijun Hu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: andy-shev

include/linux/fwnode.h

@@ -2,6 +2,11 @@
 /*
  * fwnode.h - Firmware device node object handle type definition.
  *
+ * This header file provides low-level data types and definitions for firmware
+ * and device property providers. The respective API header files supplied by
+ * them should contain all of the requisite data types and definitions for end
+ * users, so including it directly should not be necessary.
+ *
  * Copyright (C) 2015, Intel Corporation
  * Author: Rafael J. Wysocki <[email protected]>
  */