1 files changed, 7 insertions, 0 deletions
diff --git a/include/linux/stm.h b/include/linux/stm.h
index 9d0083d364e6..ab8ceca4f570 100644
--- a/include/linux/stm.h
+++ b/include/linux/stm.h
@@ -67,6 +67,13 @@ struct stm_device;
  * description. That is, the lowest master that can be allocated to software
  * writers is @sw_start and data from this writer will appear is @sw_start
  * master in the STP stream.
+ *
+ * The @packet callback should adhere to the following rules:
+ *   1) it must return the number of bytes it consumed from the payload;
+ *   2) therefore, if it sent a packet that does not have payload (like FLAG),
+ *      it must return zero;
+ *   3) if it does not support the requested packet type/flag combination,
+ *      it must return -ENOTSUPP.
  */
 struct stm_data {
 	const char		*name;