quoted

We just need a set of type names for the sysfs node I think "bluetooth", "ups",
"loconet", "serial", "modem", "cir" etc...

Is it a good idea to introduce uart_device driver in the kernel to fill a new 'ldisc' member in the uart_device or to load ldisc by default for the corresponding tty_port?

No but it can provide information to help user space. In many cases the
decision isn't about a line discipline but about automatically setting
permissions or linking ports to the right driver.

The hints need to be generic - they can come from open firmware, from pci
identifiers, from ACPI and so on.

Shall we change the uart_bus to the tty_bus, then introduce tty_host / tty_target for the bus?

We have a tty class - is that not sufficient ?

Alan