diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 50eb0e5..196ba17 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -203,6 +203,14 @@
   enabled and the driver is using NAPI. The struct contains also two
   other fields, but they are reserved and undefined.
 
+SOF_TIMESTAMPING_OPT_TX_SWHW:
+
+  Request both hardware and software timestamps for outgoing packets
+  when SOF_TIMESTAMPING_TX_HARDWARE and SOF_TIMESTAMPING_TX_SOFTWARE
+  are enabled at the same time. If both timestamps are generated,
+  two separate messages will be looped to the socket's error queue,
+  each containing just one timestamp.
+
 New applications are encouraged to pass SOF_TIMESTAMPING_OPT_ID to
 disambiguate timestamps and SOF_TIMESTAMPING_OPT_TSONLY to operate
 regardless of the setting of sysctl net.core.tstamp_allow_data.