Documentation: devres: note checking needs when converting

There are a number of cases where conversions to devm_* API have been
done but developers forgot that this conversion may imply that return
values need to be checked for failure of internal resource handling
like allocation. While this should be clear, it does seem to be a
relatively common issue with API conversions or maybe "managed" is
being misunderstood ? So add a note to make the scope of "managed" clear.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/driver-model/devres.txt

@@ -132,6 +132,13 @@ devres.  Complexity is shifted from less maintained low level drivers
 to better maintained higher layer.  Also, as init failure path is
 shared with exit path, both can get more testing.
 
+Note though that when converting current calls or assignments to
+managed devm_* versions it is up to you to check if internal operations
+like allocating memory, have failed. Managed resources pertains to the
+freeing of these resources *only* - all other checks needed are still
+on you. In some cases this may mean introducing checks that were not
+necessary before moving to the managed devm_* calls.
+
 
   3. Devres group
   ---------------