serial: 8250: reset uart when set baud rate

If external device sends data continuously, then uart is
always busy, and baud rate can't be set. It is useful
to reset uart and set loop back mode to make sure it is
idle.

Change-Id: I87286711870ff685ea29e36e61c97d45be5a6d08
Signed-off-by: Huibin Hong <huibin.hong@rock-chips.com>

Author: Huibin Hong

drivers/tty/serial/8250/8250_port.c

@@ -2207,6 +2207,10 @@ static void serial8250_set_divisor(struct uart_port *port, unsigned int baud,
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 
+#ifdef CONFIG_ARCH_ROCKCHIP
+	serial_port_out(port, UART_MCR, UART_MCR_LOOP);
+#endif
+
 	/* Workaround to enable 115200 baud on OMAP1510 internal ports */
 	if (is_omap1510_8250(up)) {
 		if (baud == 115200) {
@@ -2227,6 +2231,13 @@ static void serial8250_set_divisor(struct uart_port *port, unsigned int baud,
 
 	serial_dl_write(up, quot);
 
+#ifdef CONFIG_ARCH_ROCKCHIP
+	serial_port_out(port, UART_MCR, up->mcr);
+	if (quot != serial_dl_read(up))
+		pr_warn_ratelimited("ttyS%d set divisor fail, quot:%d != dll,dlh:%d\n",
+					 serial_index(port), quot, serial_dl_read(up));
+#endif
+
 	/* XR17V35x UARTs have an extra fractional divisor register (DLD) */
 	if (up->port.type == PORT_XR17V35X) {
 		/* Preserve bits not related to baudrate; DLD[7:4]. */
@@ -2330,6 +2341,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	if ((termios->c_cflag & CREAD) == 0)
 		port->ignore_status_mask |= UART_LSR_DR;
 
+#ifndef CONFIG_ARCH_ROCKCHIP
 	/*
 	 * CTS flow control flag and modem status interrupts
 	 */
@@ -2343,6 +2355,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 		up->ier |= UART_IER_RTOIE;
 
 	serial_port_out(port, UART_IER, up->ier);
+#endif
 
 	if (up->capabilities & UART_CAP_EFR) {
 		unsigned char efr = 0;
@@ -2361,7 +2374,13 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 			serial_port_out(port, UART_EFR, efr);
 	}
 
+#ifdef CONFIG_ARCH_ROCKCHIP
+	/* Reset uart to make sure it is idle, then set buad rate */
+	serial_port_out(port, 0x88 >> 2, 0x7);
+#endif
+
 	serial8250_set_divisor(port, baud, quot, frac);
+
 #ifdef CONFIG_ARCH_ROCKCHIP
 	up->fcr = UART_FCR_ENABLE_FIFO | UART_FCR_T_TRIG_10 | UART_FCR_R_TRIG_10;
 #endif
@@ -2380,6 +2399,23 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 		serial_port_out(port, UART_FCR, up->fcr);	/* set fcr */
 	}
 	serial8250_set_mctrl(port, port->mctrl);
+
+#ifdef CONFIG_ARCH_ROCKCHIP
+	/*
+	 * CTS flow control flag and modem status interrupts
+	 */
+	up->ier &= ~UART_IER_MSI;
+	if (!(up->bugs & UART_BUG_NOMSR) &&
+			UART_ENABLE_MS(&up->port, termios->c_cflag))
+		up->ier |= UART_IER_MSI;
+	if (up->capabilities & UART_CAP_UUE)
+		up->ier |= UART_IER_UUE;
+	if (up->capabilities & UART_CAP_RTOIE)
+		up->ier |= UART_IER_RTOIE;
+
+	serial_port_out(port, UART_IER, up->ier);
+#endif
+
 	spin_unlock_irqrestore(&port->lock, flags);
 	serial8250_rpm_put(up);