usb to serial converter doesn't enumerate

bigbrettt · 2023-05-22 21:52:35

I can't seem to find my PL2303 usb-to-serial converter anywhere in /dev/tty. I thought it should show up as /dev/ttyUSB0 (or similar) but it doesn't. My user is already a member of uucp.

dmesg shows the following when I plug it in:

[2420518.790602] usb 1-1: new full-speed USB device number 7 using xhci_hcd
[2420518.934685] usb 1-1: New USB device found, idVendor=067b, idProduct=2303, bcdDevice= 4.00
[2420518.934699] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[2420518.934705] usb 1-1: Product: USB-Serial Controller
[2420518.934710] usb 1-1: Manufacturer: Prolific Technology Inc.

But again, nothing about which tty it is bound to. Any tips for using it appreciated.

System:
Linux archlinux 6.1.25-1-lts #1 SMP PREEMPT_DYNAMIC Thu, 20 Apr 2023 14:01:39 +0000 x86_64 GNU/Linux

Last edited by bigbrettt (2023-05-22 22:01:53)

ewaller · 2023-05-22 22:01:44

And the output of pacman -Q linux-lts ? Does it match the version number of the uname output you provided?

bigbrettt · 2023-05-22 22:03:43

ewaller wrote:

And the output of pacman -Q linux-lts ? Does it match the version number of the uname output you provided?

...interesting, it does not. Output of that shows "linux-lts 6.1.27-1". Is something about my system misconfigured?

bigbrettt · 2023-05-22 22:08:44

I should also mention that this happens with multiple brands of adapter, so not a HW issue

ewaller · 2023-05-22 22:40:39

Yeah, what is happening is the kernel is looking for its loadable modules in response to a device being attached. At some point, your kernel has been upgraded. When that happens, a couple things happen. The modules for the old kernel are removed. The modules for the new kernel are installed, and (the important one) The new kernel is written to /boot. This makes the assumption that your boot partition is mounted on /boot. If it is not, the new kernel is written to the DIRECTORY called /boot, but does not get written to the boot partition since it was not mounted. Because of this, the kernel cannot find the necessary module (driver).

You can check this with the mount command. I also bet there is not a line in /etc/fstab that causes the boot partition to be mounted. What happens is the boot process loads the old kernel from the boot volume, mounts /root and starts the init process. Unfortunately, your root partition has the newer modules.

To fix this, mount your boot partition on /boot and reinstall the kernel. Reboot and see if things work (and if uname reports the newer kernel)
Then, to really fix it, you will want to remove the kernel and init ram disk image from /boot (since they are never used and are a waste of space), then fix /etc/fstab to automatically mount the boot partition so this never happens again.

That is the 10,000 ft view. We can help with any specifics.

Last edited by ewaller (2023-05-22 22:43:55)

bigbrettt · 2023-05-22 22:45:53

okay, didn't expect to run into this when just faffing around with serial ports! I see the problem now when I try to modprobe usbserial...it is looking in the wrong location for modules (one that doesn't exist since the kernel version is different).

If I boot regular kernel (not LTS) it all seem to work, so might just remove the (misconfigured) lts kernel and call it a day. I'll make a new issue if I have problems. Thanks!

Last edited by bigbrettt (2023-05-22 22:58:40)

ewaller · 2023-05-22 22:55:32

Okay, but be advised.... The same /etc/fstab file is used regardless of the kernel, so you should have the same issue if you update the mainline kernel. Both the mainline kernel and the lts kernel are written to /boot -- they just have different file names. The kernel that gets loaded is selected by the bootloader.

Arch Linux

#1 2023-05-22 21:52:35

usb to serial converter doesn't enumerate

#2 2023-05-22 22:01:44

Re: usb to serial converter doesn't enumerate

#3 2023-05-22 22:03:43

Re: usb to serial converter doesn't enumerate

#4 2023-05-22 22:08:44

Re: usb to serial converter doesn't enumerate

#5 2023-05-22 22:40:39

Re: usb to serial converter doesn't enumerate

#6 2023-05-22 22:45:53

Re: usb to serial converter doesn't enumerate

#7 2023-05-22 22:55:32

Re: usb to serial converter doesn't enumerate

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