Many devices containing switches have a cable test function available in the UI of the stock firmware, that leverages VCT functions available in e.g. the AR9331, QCA8337, and other chips.
I tried searching for tool, that I could use on Openwrt to (automatically?) measure cable lengths for all devices/individual_ports, but wasn't successful. Or is this built in, and some SNMP MIB makes this info available, if enabled somewhere?
Does somebody know a way? Or could I cobble (easily?) something together using some command-line MDIO-Write/Read tool?
Testing on Openwrt complains about missing netlink support in ethtool, which doesn't seem to be an explicit option in the build system, but may be included in ethtool-full. I'll try that later today.