Documentation/admin-guide: Document Thunderbolt/USB4 tunneling events

Add documentation about the Thunderbolt/USB4 tunneling events to the
user’s and administrator’s guide.

Signed-off-by: Alan Borzeszkowski <alan.borzeszkowski@linux.intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/Documentation/admin-guide/thunderbolt.rst b/Documentation/admin-guide/thunderbolt.rst
index d0502691dfa1..240fee618e06 100644
--- a/Documentation/admin-guide/thunderbolt.rst
+++ b/Documentation/admin-guide/thunderbolt.rst
@@ -296,6 +296,39 @@ information is missing.
 To recover from this mode, one needs to flash a valid NVM image to the
 host controller in the same way it is done in the previous chapter.
 
+Tunneling events
+----------------
+The driver sends ``KOBJ_CHANGE`` events to userspace when there is a
+tunneling change in the ``thunderbolt_domain``. The notification carries
+following environment variables::
+
+  TUNNEL_EVENT=<EVENT>
+  TUNNEL_DETAILS=0:12 <-> 1:20 (USB3)
+
+Possible values for ``<EVENT>`` are:
+
+  activated
+    The tunnel was activated (created).
+
+  changed
+    There is a change in this tunnel. For example bandwidth allocation was
+    changed.
+
+  deactivated
+    The tunnel was torn down.
+
+  low bandwidth
+    The tunnel is not getting optimal bandwidth.
+
+  insufficient bandwidth
+    There is not enough bandwidth for the current tunnel requirements.
+
+The ``TUNNEL_DETAILS`` is only provided if the tunnel is known. For
+example, in case of Firmware Connection Manager this is missing or does
+not provide full tunnel information. In case of Software Connection Manager
+this includes full tunnel details. The format currently matches what the
+driver uses when logging. This may change over time.
+
 Networking over Thunderbolt cable
 ---------------------------------
 Thunderbolt technology allows software communication between two hosts