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can: add termination resistor documentation 

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

Signed-off-by: Daniel Trevitz <dan@sstrev.com>
Link: https://lore.kernel.org/all/3441354.44csPzL39Z@daniel6430
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Daniel S. Trevitz 2022-10-07 07:53:02 -04:00 committed by Marc Kleine-Budde
parent a526a3cc9c
commit 85700ac19a
1 changed files with 33 additions and 0 deletions
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33
Documentation/networking/can.rst
View File

@ -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)
-----------------------------