Enable 9bit-mode in a serial device

Hi all, I'm wondering what's the best way to enable the 9bit-mode for a given tty serial device. I have a motherboard with a NCT6102D Nuvoton super IO with 6 UARTs. This device is supported by the 8250/16550 driver already in kernel and I'm able to communicate two serial port with a NULL modem cable.

From NCT6102D Nuvoton datasheet it seems some bits has to be set in order to enable this mode to use the parity bit as the 9 bit.

Any hint? Any driver from drivers/tty/serial/8250 can be used as a guide? Some user space code can be used to get access to registers? Thanks, Jorge