[PATCH 1/1 v2] Termination resistor documentation

[PATCH 1/1 v2] Termination resistor documentation

[Daniel S. Trevitz]

Add documentation for how to use and setup the switchable termination
resistor support for the can-controllers.

Signed-off-by: Daniel Trevitz <dan@sstrev.com>
---
 Documentation/networking/can.rst | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
index ebc822e605f5..bb39cfa4c502 100644
--- a/Documentation/networking/can.rst
+++ b/Documentation/networking/can.rst
@@ -1148,6 +1148,36 @@ tuning on deep embedded systems'. The author is running a MPC603e
 load without any problems ...


+Switchable Termination Resistors
+--------------------------------
+
+CAN bus requires a specific impedance across the differential pair,
+typically provided by two 120Ohm resistors on the farthest nodes of
+the bus. Some CAN controllers support activating / deactivating a
+termination resistor(s) to provide the correct impedance::
+
+  - Query the available resistances:
+      $ ip -details link show can0
+      ...
+      termination 120 [ 0, 120 ]
+
+  - Activate the terminating resistor:
+      $ ip link set dev can0 type can termination 120
+
+  - Deactivate the terminating resistor:
+      $ ip link set dev can0 type can termination 0
+
+To enable termination resistor support to a can-controller, either
+implement in the controller's struct can-priv::
+
+    termination_const
+    termination_const_cnt
+    do_set_termination
+
+or add gpio control with the device tree entries from
+Documentation/devicetree/bindings/net/can/can-controller.yaml
+
+
 The Virtual CAN Driver (vcan)
 -----------------------------

--
2.35.1