netdev - [PATCH net-next 01/29] can: add termination resistor documentation

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Message-Id: <20221026084007.1583333-2-mkl@pengutronix.de>
Date:   Wed, 26 Oct 2022 10:39:39 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, "Daniel S. Trevitz" <dan@...rev.com>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net-next 01/29] can: add termination resistor documentation

From: "Daniel S. Trevitz" <dan@...rev.com>

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

Signed-off-by: Daniel Trevitz <dan@...rev.com>
Link: https://lore.kernel.org/all/3441354.44csPzL39Z@daniel6430
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 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)
 -----------------------------
 

base-commit: a526a3cc9c8d426713f8bebc18ebbe39a8495d82
-- 
2.35.1