Add documentation for how to use and setup the switchable termination resistor support for the can-controllers. Signed-off-by: Daniel Trevitz <dan@xxxxxxxxxx> --- 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
