Re: [PATCH 1/1] Termination resistor documentation

["Daniel S. Trevitz" <dan@sstrev.com>]

On Friday, October 7, 2022 3:41:17 AM EDT Marc Kleine-Budde wrote:
> On 06.10.2022 15:27:50, Daniel S. Trevitz wrote:
> > 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 | 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:
> You need double :: followed by a newline to mark as code.
This whole section is a code block; :: is up three lines.
> 
> > +      $ ip -details link show can0
> > +      ...
> > +      termination 120 [ 0, 120
> 
> The closing ] is missing, please add it, even if the current ip command
> doesn't print it. I just noticed it got lost in a cleanup patch in
> iproute2.
Okay
> 
> > +
> 
> > +  - Activate the terminating resistor:
> same here
> 
> > +      $ ip link set dev can0 type can termination 120
> > +
> 
> > +  - Deactivate the terminating resistor:
> same here
> 
> > +      $ 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)
> >  -----------------------------
> 
> Marc

-Dan