Report extra baud rates supported above the base rate for ports with the UPF_MAGIC_MULTIPLIER property, so that people have a way to find out that they can be used with their system, e.g.: Serial: 8250/16550 driver, 5 ports, IRQ sharing enabled printk: console [ttyS0] disabled serial8250.0: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A serial8250.0: ttyS0 extra baud rates supported: 230400, 460800 printk: console [ttyS0] enabled printk: bootconsole [uart8250] disabled serial8250.0: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A serial8250.0: ttyS1 extra baud rates supported: 230400, 460800 serial8250.0: ttyS2 at MMIO 0x1f000900 (irq = 20, base_baud = 230400) is a 16550A Otherwise there is no clear way to figure this out, as the feature is only reported as an obscure TTY flag in bit 16: $ cat /sys/class/tty/ttyS[0-2]/flags 0x10010040 0x10010040 0x90000040 $ Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx> --- drivers/tty/serial/serial_core.c | 8 ++++++++ 1 file changed, 8 insertions(+) linux-serial-core-magic-multiplier.diff Index: linux-macro-ide-tty/drivers/tty/serial/serial_core.c =================================================================== --- linux-macro-ide-tty.orig/drivers/tty/serial/serial_core.c +++ linux-macro-ide-tty/drivers/tty/serial/serial_core.c @@ -2314,6 +2314,14 @@ uart_report_port(struct uart_driver *drv port->dev ? ": " : "", port->name, address, port->irq, port->uartclk / 16, uart_type(port)); + + /* The magic multiplier feature is a bit obscure, so report it too. */ + if (port->flags & UPF_MAGIC_MULTIPLIER) + pr_info("%s%s%s extra baud rates supported: %d, %d", + port->dev ? dev_name(port->dev) : "", + port->dev ? ": " : "", + port->name, + port->uartclk / 8, port->uartclk / 4); } static void