debugfs: Document that debugfs_create functions need not be error checked

As talked about in commit b792e64021 ("drm: no need to check return
value of debugfs_create functions"), in many cases we can get away
with totally skipping checking the errors of debugfs functions. Let's
document that so people don't add new code that needlessly checks
these errors.

Probably this note could be added to a boatload of functions, but
that's a lot of duplication.  Let's just add it to the two most
frequent ones and hope people will get the idea.

Suggested-by: Javier Martinez Canillas <[email protected]>
Reviewed-by: Javier Martinez Canillas <[email protected]>
Signed-off-by: Douglas Anderson <[email protected]>
Link: https://lore.kernel.org/r/20220222154555.1.I26d364db7a007f8995e8f0dac978673bc8e9f5e2@changeid
Signed-off-by: Greg Kroah-Hartman <[email protected]>

fs/debugfs/inode.c

@@ -450,6 +450,11 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
+ *
+ * NOTE: it's expected that most callers should _ignore_ the errors returned
+ * by this function. Other debugfs functions handle the fact that the "dentry"
+ * passed to them could be an error and they don't crash in that case.
+ * Drivers should generally work fine even if debugfs fails to init anyway.
  */
 struct dentry *debugfs_create_file(const char *name, umode_t mode,
 				   struct dentry *parent, void *data,
@@ -551,6 +556,11 @@ EXPORT_SYMBOL_GPL(debugfs_create_file_size);
  *
  * If debugfs is not enabled in the kernel, the value -%ENODEV will be
  * returned.
+ *
+ * NOTE: it's expected that most callers should _ignore_ the errors returned
+ * by this function. Other debugfs functions handle the fact that the "dentry"
+ * passed to them could be an error and they don't crash in that case.
+ * Drivers should generally work fine even if debugfs fails to init anyway.
  */
 struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
 {