tty: serial: altera_uart: Use port->regshift to store bus shift

Use the regshift member of struct uart_port to store the address stride
from platform data. This way we can save one dereference per call of
altera_uart_readl and altera_uart_writel.

This also allows us to use the driver without platform data, which is
needed for device tree support in the Nios2 port.
Acked-by: NAnton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: NTobias Klauser <tklauser@distanz.ch>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/tty/serial/altera_uart.c

@@ -86,16 +86,12 @@ struct altera_uart {
 
 static u32 altera_uart_readl(struct uart_port *port, int reg)
 {
-	struct altera_uart_platform_uart *platp = port->private_data;
-
-	return readl(port->membase + (reg << platp->bus_shift));
+	return readl(port->membase + (reg << port->regshift));
 }
 
 static void altera_uart_writel(struct uart_port *port, u32 dat, int reg)
 {
-	struct altera_uart_platform_uart *platp = port->private_data;
-
-	writel(dat, port->membase + (reg << platp->bus_shift));
+	writel(dat, port->membase + (reg << port->regshift));
 }
 
 static unsigned int altera_uart_tx_empty(struct uart_port *port)
@@ -546,13 +542,17 @@ static int __devinit altera_uart_probe(struct platform_device *pdev)
 	if (!port->membase)
 		return -ENOMEM;
 
+	if (platp)
+		port->regshift = platp->bus_shift;
+	else
+		port->regshift = 0;
+
 	port->line = i;
 	port->type = PORT_ALTERA_UART;
 	port->iotype = SERIAL_IO_MEM;
 	port->uartclk = platp->uartclk;
 	port->ops = &altera_uart_ops;
 	port->flags = UPF_BOOT_AUTOCONF;
-	port->private_data = platp;
 
 	uart_add_one_port(&altera_uart_driver, port);