Source: linux Version: 4.18.10-2 Severity: normal Dear Maintainer, Since the upgrade of our system from Debian 9 (Stretch) to 10 (Buster), but also from Ubuntu 16.04 LTS (Xenial) to 18.04 LTS (Bionic), the serial port of our Atom E3950-based board can no longer be used. I have traced the cause to the enabling of CONFIG_SERIAL_DEV_BUS=y and CONFIG_SERIAL_DEV_CTRL_TTYPORT=y in the kernel config of versions 4.17.0-3 (Debian) and 4.15.0.36.38 (Ubuntu).
A fix was merged for this in upstream kernel. See commitc5ee0b3104e0b ("serdev: Don't claim unsupported ACPI serial devices") It was also backported to v4.19 stable kernel (released in v4.19.96).