* [PATCH 1/1 v3] Termination resistor documentation
@ 2022-10-07 11:53 Daniel S. Trevitz
2022-10-07 11:57 ` Marc Kleine-Budde
0 siblings, 1 reply; 2+ messages in thread
From: Daniel S. Trevitz @ 2022-10-07 11:53 UTC (permalink / raw)
To: linux-can; +Cc: Marc Kleine-Budde, Daniel Trevitz, Ryan Edwards
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 | 33 ++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/Documentation/networking/can.rst b/Documentation/networking/can.rst
index ebc822e605f5..90121deef217 100644
--- a/Documentation/networking/can.rst
+++ b/Documentation/networking/can.rst
@@ -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)
-----------------------------
--
2.35.1
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2022-10-07 11:53 [PATCH 1/1 v3] Termination resistor documentation Daniel S. Trevitz
2022-10-07 11:57 ` Marc Kleine-Budde
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