enumerated and userspace can obtain the hotplug event of the UART
target devices. Linux kernel is lack of an overall enumeration
mechanism for UART target devices.

ls /sys/class/tty/

In order to send uevent, a device need to be a class device or a bus
device. This patch introduces a bus_type subsystem to manage the new

I still don't see why the existing tty class interfaces cannot be used,
the hints from ACPI (or anywhere else) cannot be attached as properties
to the tty driver and device sysfs

Alan