Commit 85700ac1 authored by Daniel S. Trevitz's avatar Daniel S. Trevitz Committed by Marc Kleine-Budde
Browse files

can: add termination resistor documentation 



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

Signed-off-by: default avatarDaniel Trevitz <dan@sstrev.com>
Link: https://lore.kernel.org/all/3441354.44csPzL39Z@daniel6430


Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent a526a3cc

Documentation/networking/can.rst

+33 −0
Original line number Diff line number Diff line
@@ -1148,6 +1148,39 @@ 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)

-----------------------------