Problem with the CH341 driver in Ubuntu 20.04

[Augusto Ciuffoletti]

I run into this problem trying to program an ESP8266 board, which uses
the CH341 chip in the programming interface as a USB-to-Serial
interface. The problem appeared after an upgrade from Ubuntu 19.10 to
20.04 (that I carried out one week ago).

This is the kernel I am using:

===
$ uname -r
5.4.0-58-generic
===

When I connect the ESP8266 board (a Wemos D1 mini) to the USB there is
no activity on the syslog (or dmesg), and the kernel module is not
loaded. In fact I do not see the /dev/ttyACM0 device in the /dev
directory and no useful device appears in the Arduino GUI.

I have found the module in the kernel tree but, even forcing the
installation, nothing happens:

===
augusto at Legion:~$ ls
/usr/lib/modules/5.4.0-58-generic/kernel/drivers/usb/serial/ch*
/usr/lib/modules/5.4.0-58-generic/kernel/drivers/usb/serial/ch341.ko
augusto at Legion:~$ sudo modprobe ch341
[sudo] password di augusto:
augusto at Legion:~$ lsusb
Bus 002 Device 002: ID 05e3:0626 Genesys Logic, Inc. USB3.1 Hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 003: ID 13d3:56a6 IMC Networks Integrated Camera
Bus 001 Device 005: ID 0cf3:e500 Qualcomm Atheros Communications
Bus 001 Device 006: ID 046d:c517 Logitech, Inc. LX710 Cordless Desktop Laser
Bus 001 Device 004: ID 093a:2510 Pixart Imaging, Inc. Optical Mouse
Bus 001 Device 002: ID 05e3:0610 Genesys Logic, Inc. 4-port hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
augusto at Legion:~$ lsmod | grep ch34
ch341                  20480  0
usbserial              53248  1 ch341
===

Without this module it is impossible to work with a relevant number of
SBC devices, besides the named Wemos D1 Mini.

Trying to solve the problem I also downloaded and installed the module
source from https://github.com/juliagoda/CH341SER and compiled on my
PC, after removing the "secure boot" feature.

Thank you for any help.

Note: I originally posted this question on AskUbuntu
(https://askubuntu.com/questions/1304116/problem-with-the-ch341-driver-in-ubuntu-20-04),
but with no answer after 40+ views. I bounced to the
linux-usb at vger.kernel.org maillist which suggested submitting the
problem to the Ubuntu kernel team. Here I am...