[U-Boot] [PATCH v4 14/18] serial: 16550: allow the driver to support MediaTek serial

[Ryder Lee]

This patch adds an extra operation in ns16550.c to suuport MediaTek
SoCs as we have a highspeed register which influences the calcualtion
of the divisor.

Note that we don't support the baudrate greater than 115200 currently.

Signed-off-by: Ryder Lee <ryder.lee at mediatek.com>
Tested-by: Matthias Brugger <matthias.bgg at gmail.com>
Reviewed-by: Simon Glass <sjg at chromium.org>
---
Changes since v4: None

@Simon
We have tried the compatible string, but it made the ns16550 driver more complicated.
To use the compatible string we have to add a new field in ns16550_platdata, and change
the flow of ns16550_serial_probe().

Moreover, it's totally useless for debug uart. At present using a macro is the easiest way here.

What do you think?
---
 drivers/serial/ns16550.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
index f9041aa..f5410af 100644
--- a/drivers/serial/ns16550.c
+++ b/drivers/serial/ns16550.c
@@ -148,6 +148,13 @@ int ns16550_calc_divisor(NS16550_t port, int clock, int baudrate)
 
 static void NS16550_setbrg(NS16550_t com_port, int baud_divisor)
 {
+#ifdef CONFIG_ARCH_MEDIATEK
+	/*
+	 * MediaTek UARTs has an extra highspeed register.
+	 * We need to clear it if baudrate <= 115200.
+	 */
+	serial_out(0, &com_port->reg9);
+#endif
 	serial_out(UART_LCR_BKSE | UART_LCRVAL, &com_port->lcr);
 	serial_out(baud_divisor & 0xff, &com_port->dll);
 	serial_out((baud_divisor >> 8) & 0xff, &com_port->dlm);
@@ -261,6 +268,9 @@ static inline void _debug_uart_init(void)
 	serial_dout(&com_port->mcr, UART_MCRVAL);
 	serial_dout(&com_port->fcr, UART_FCR_DEFVAL);
 
+#ifdef CONFIG_ARCH_MEDIATEK
+	serial_dout(&com_port->reg9, 0);
+#endif
 	serial_dout(&com_port->lcr, UART_LCR_BKSE | UART_LCRVAL);
 	serial_dout(&com_port->dll, baud_divisor & 0xff);
 	serial_dout(&com_port->dlm, (baud_divisor >> 8) & 0xff);
-- 
1.9.1