serial: core: Add minor field to uart_port

UART drivers that share ttyS namespace cannot trivially compute the
ttyS index from the port->line value since the minor_start may be
offset from minor 64. Further, to do so requires a pointer to the
uart driver since there is no back pointer from uart_port to
uart_driver.

Rather than have UART drivers computing the minor value by themselves,
encapsulate within the serial core at port registration time.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_core.c

@@ -2682,6 +2682,7 @@ int uart_add_one_port(struct uart_driver *drv, struct uart_port *uport)
 
 	state->pm_state = UART_PM_STATE_UNDEFINED;
 	uport->cons = drv->cons;
+	uport->minor = drv->tty_driver->minor_start + uport->line;
 
 	/*
 	 * If this port is a console, then the spinlock is already

include/linux/serial_core.h

@@ -235,6 +235,7 @@ struct uart_port {
 	const struct uart_ops	*ops;
 	unsigned int		custom_divisor;
 	unsigned int		line;			/* port index */
+	unsigned int		minor;
 	resource_size_t		mapbase;		/* for ioremap */
 	struct device		*dev;			/* parent device */
 	unsigned char		hub6;			/* this should be in the 8250 driver */