All devices behind a SPI controller have the same udev ID_PATH property.
This is a problem for predicable network names for CAN controllers.
CAN controllers, in contrast to Ethernet controllers, don't have a MAC
Address, so there's no way to tell two CAN controllers on the same SPI
host controller apart:
$ udevadm info /sys/class/net/can0
P: /devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.1/net/can0
L: 0
E: DEVPATH=/devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.1/net/can0
E: INTERFACE=can0
E: IFINDEX=3
E: SUBSYSTEM=net
E: USEC_INITIALIZED=11187199
E: ID_PATH=platform-fe204000.spi
E: ID_PATH_TAG=platform-fe204000_spi
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/can0
E: TAGS=:systemd:
$ udevadm info /sys/class/net/can1
P: /devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.0/net/can1
L: 0
E: DEVPATH=/devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.0/net/can1
E: INTERFACE=can1
E: IFINDEX=4
E: SUBSYSTEM=net
E: USEC_INITIALIZED=11192211
E: ID_PATH=platform-fe204000.spi
E: ID_PATH_TAG=platform-fe204000_spi
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/can1
E: TAGS=:systemd:
With this the chip select number is added to the ID_PATH, to make
predictable network names possible.
$ sudo udevadm info /sys/class/net/can0
P: /devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.1/net/can0
L: 0
E: DEVPATH=/devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.1/net/can0
E: INTERFACE=can0
E: IFINDEX=3
E: SUBSYSTEM=net
E: USEC_INITIALIZED=11187199
E: ID_PATH=platform-fe204000.spi-cs-1
E: ID_PATH_TAG=platform-fe204000_spi-cs-1
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/can0
E: TAGS=:systemd:
$ sudo udevadm info /sys/class/net/can1
P: /devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.0/net/can1
L: 0
E: DEVPATH=/devices/platform/soc/fe204000.spi/spi_master/spi0/spi0.0/net/can1
E: INTERFACE=can1
E: IFINDEX=4
E: SUBSYSTEM=net
E: USEC_INITIALIZED=11192211
E: ID_PATH=platform-fe204000.spi-cs-0
E: ID_PATH_TAG=platform-fe204000_spi-cs-0
E: SYSTEMD_ALIAS=/sys/subsystem/net/devices/can1
E: TAGS=:systemd: