On Sat, Aug 03, 2019 at 03:55:37PM +0200, Greg Kroah-Hartman wrote: > On Sat, Aug 03, 2019 at 03:23:23PM +0200, Adam Borowski wrote: > > On Fri, Aug 02, 2019 at 09:59:06PM +0200, Paul Menzel wrote: > > > Because the cable is always connected to the port on the back side, and > > > sometimes the port in the front has ID 0, and the one in the back 1, and > > > other times vice versa. We do not want to track that, and it would be > > > convenient to just write to both ports. > > > > Sounds like an XY problem then: what you want is not writing to all ports, > > but to have the port assignments stable (see also: disk device reordering). > > You can get that information from the symlinks in /dev/serial/ which > udev creates. Doesn't seem to work for me, for any ttyS0 ttyS1 ttySAC1 device: Box one, PCIe card + one USB dongle: 07:00.0 Serial controller: MosChip Semiconductor Technology Ltd. MCS9922 PCIe Multi-I/O Controller 07:00.1 Serial controller: MosChip Semiconductor Technology Ltd. MCS9922 PCIe Multi-I/O Controller Bus 003 Device 004: ID 1a86:7523 QinHeng Electronics HL-340 USB-Serial adapter /dev/serial/by-id/usb-1a86_USB2.0-Serial-if00-port0 /dev/serial/by-path/pci-0000:0b:00.3-usb-0:4:1.0-port0 Only ttyUSB0 is there. Box two, on-board + one USB dongle: [ 3.404340] Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled [ 3.431287] 00:01: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A Bus 001 Device 002: ID 10c4:ea60 Cygnal Integrated Products, Inc. CP2102/CP2109 UART Bridge Controller [CP210x family] /dev/serial/by-id/usb-Silicon_Labs_CP2104_USB_to_UART_Bridge_Controller_00DB1604-if00-port0 /dev/serial/by-path/pci-0000:00:14.0-usb-0:1:1.0-port0 Box three: RockPro64, euler + USB dongle, kernel 4.4. Box four: Pine64, euler. Box five: Odroid-U2, something GPIOish (ttySAC1), kernel 5.0. Most are running kernel 5.2, Debian unstable. And indeed, in /lib/udev/rules.d/60-serial.rules : # /dev/serial/by-path/, /dev/serial/by-id/ for USB devices KERNEL!="ttyUSB[0-9]*|ttyACM[0-9]*", GOTO="serial_end" Like me, Paul is using ttyS0 for server-side. Meow! -- ⢀⣴⠾⠻⢶⣦⠀ ⣾⠁⢰⠒⠀⣿⡁ 10 people enter a bar: 1 who understands binary, ⢿⡄⠘⠷⠚⠋⠀ 1 who doesn't, D who prefer to write it as hex, ⠈⠳⣄⠀⠀⠀⠀ and 1 who narrowly avoided an off-by-one error.
