uart: pl011: Improve LCRH register access decision

Improve LCRH register access decision as ARM PL011 lcrh
register serve as both TX and RX, while other SOC may
implement TX and RX function with separated register.
Signed-off-by: Jun Nie <jun.nie@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -249,6 +249,11 @@ struct uart_amba_port {
 #endif
 };
 
+static bool is_implemented(struct uart_amba_port *uap, unsigned int reg)
+{
+	return uap->reg_lut[reg] != (u16)~0;
+}
+
 static unsigned int pl011_readw(struct uart_amba_port *uap, int index)
 {
 	WARN_ON(index > REG_NR);
@@ -1649,7 +1654,7 @@ static int pl011_hwinit(struct uart_port *port)
 static void pl011_write_lcr_h(struct uart_amba_port *uap, unsigned int lcr_h)
 {
 	pl011_writew(uap, lcr_h, uap->lcrh_rx);
-	if (uap->lcrh_rx != uap->lcrh_tx) {
+	if (is_implemented(uap, REG_ST_LCRH_RX)) {
 		int i;
 		/*
 		 * Wait 10 PCLKs before writing LCRH_TX register,
@@ -1784,7 +1789,7 @@ static void pl011_disable_uart(struct uart_amba_port *uap)
 	 * disable break condition and fifos
 	 */
 	pl011_shutdown_channel(uap, uap->lcrh_rx);
-	if (uap->lcrh_rx != uap->lcrh_tx)
+	if (is_implemented(uap, REG_ST_LCRH_RX))
 		pl011_shutdown_channel(uap, uap->lcrh_tx);
 }