device name changes sporadically

[parhamk75]

Description

The device file name under /dev changes sporadically; Rebooting the system fixes the issue, but it'll change again after a while. I didn't have this issue on the RPi I was using before; That's why I think it might be because of the driver and the kernel version.

Before:

After: (The numbers are shifted by 8 which is the number of the channels on the device)

Setup

• I'm using WaveShare's USB TO 8CH RS485 which uses CH348L
• Ubuntu 24.04 (Kernel: 6.14.0)
• Driver commit: 4e7a4890ada6d6db3fde50beb1c7f7ec21b68816

The RPi setup I was using before:

[WCHSoftGroup]

Hi, this happens because you plugged and unplugged the USB device while opening the tty device. Re-plugging the device changes the minor device number the driver obtains from the system. This is normal. To completely fix this, you can use the udev rules file or modify the driver to force a specific minor number (but this may have side effects).

[mattwelly]

Hi, there is no unique id like interface# to use with udev role, any suggestions? can the driver be patched to provide a unique and stable path?

[WCHSoftGroup]

Yes, this chip does indeed have only one single interface, and all serial ports share this interface and endpoint for communication. Udev rules like below maybe helpful.

This script is used to fix the device name under the specified USB path.

SUBSYSTEM=="usb", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="55d9", MODE="0666"

KERNEL=="ttyCH9344USB0" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM0"
KERNEL=="ttyCH9344USB1" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM1"
KERNEL=="ttyCH9344USB2" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM2"
KERNEL=="ttyCH9344USB3" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM3"
KERNEL=="ttyCH9344USB4" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM4"
KERNEL=="ttyCH9344USB5" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM5"
KERNEL=="ttyCH9344USB6" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM6"
KERNEL=="ttyCH9344USB7" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM7"

KERNEL=="ttyCH9344USB8" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM0"
KERNEL=="ttyCH9344USB9" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM1"
KERNEL=="ttyCH9344USB10" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM2"
KERNEL=="ttyCH9344USB11" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM3"
KERNEL=="ttyCH9344USB12" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM4"
KERNEL=="ttyCH9344USB13" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM5"
KERNEL=="ttyCH9344USB14" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM6"
KERNEL=="ttyCH9344USB15" KERNELS=="3-2.1:1.0", SUBSYSTEMS=="usb", MODE:="0666", SYMLINK+="ttyCHCOM7"