RFC: add support for switchable termination

[marckleinebudde]

Hello

@ryedwards and me are planing to add switchable termination to the gs_usb USB interface. The current idea is to add a new feature bit indicating support, and 2 control messages, one to set and one to get the current termination status. Similar to the IDENTIFY feature.

I'll add these to the candleLight firmware repo and send a PR when ready.

[fenugrec]

Cool. I see mention of something similar in the docs of CANdevstudio, where some drivers support usage such as
sudo ip link set can0 type can termination 1

Is that already in the socketcan layer or other linux drivers, or something entirely driver-specific ?

[marckleinebudde]

There is complete support form the user space through the kernel into the CAN drivers. The driver has to implement the do_set_termination callback and fill out the termination_const and termination_const_cnt describing the supported resistor values.