USB serial not work after install rt kernel

[tom9672]

I use a usb-to-485 needs pl2303 driver. It works as expected before installing rt kernel.
I checked there is pl2303.ko in the driver/usb/serial folder.
I use dmesg | tail, it shows unknow device of pl2303. and I use ls -l /dev/tty* , there's no ttyUSB0.
I reinstall the RPi OS system with its default kernel. it can recoganize the serial driver.

I also tried to use sudo modprobe usbserial and sudo modprobe pl2303

It seems the pl2303 driver not work after installing the rtkernel. Is there any solutions for this issue?

[kdoren]

pl2303 driver is a kernel module that is not loaded by default.

Your modprobe command should have loaded it though.

Try adding the line "pl2303" at the end of /etc/modules, and rebooting. That should load it automatically on boot.

Then you should see it working under /sys/bus/usb-serial/

This is not likely rt related. But to be sure, you can also try the llat kernel posted in releases. I think it can work better with USB devices anyway.

[tom9672]

@kdoren Thanks for your answer. BTW, can I use the 5.15.32-rt39 to replace the default kernel 5.15.xx or 5.10.xx, the xx is not 32.

[kdoren]

Yes in general you can run any kernel (kernel is largely independent of user space), but I would recommend 5.15.32 which is currently the latest. For my use case (usb audio) I actually get better results with -llat kernel. So you might want to try that as well as rt.

[tom9672]

@kdoren Thank you.
'Try adding the line "pl2303" at the end of /etc/modules, and rebooting' not work, and pl2303 at under /sys/bus/usb-serial/. the usbport still unable recognize pl2303device. demsg|tail show unknown pl2303. and no ttyUSB0. I'm using 5.15.32-rt39.

I tried both the latest rt and lt, it will show a message at the right top of the desktop says 'no kernelname/cmdline.txt'.
And the pl2303 still not work. Is the warning message causing by some errors, and how to use pl2303 in rt or llt. Do you have any suggestions about it.

[kdoren]

What make & model of usb-to-serial device are you using?

You could try 5.10 kernel (in case problem is a bug in 5.15) or -llat kernel (in case problem is with rt).

[kdoren]

I do see reports of problems with pl2303, including some introduced in 5.13 kernel but supposedly fixed. I suggest trying the 5.10.90-rt61 or 5.10.95-llat kernels, and load the pl2303 driver as above.

[kdoren]

The notification about cmdline is not a problem. If it bothers you, you can set notifications=0 in /home/pi/.config/lxpanel/LXDE-pi/panels

[tom9672]

Thank you for your reply.
I use Prolific pl2303, SC-US + isolation USB to RS485 converter,
(It works well on the RPi default kernel. When I insert the usb, I can see the serial -> ttyUSB0 )
Will try the 5.10 later, hope the device works.

[tom9672]

Boom, the pl2303 works well on 5.10.90-rt61 v8+