AT91: Small fix on AT91 USART initialization code

Before reset dbgu transmitter, we just wait TXEMPTY to drain the
transmitter register(Just in case). If not doing this, we may sometimes
see several weird characters from DBGU.

A short delay is also added to make sure the new serial settings are
settled.

Signed-off-by: Hong Xu <hong.xu@atmel.com>
[cherry-picked from u-boot-atmel/old-next]
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>

diff --git a/drivers/serial/atmel_usart.c b/drivers/serial/atmel_usart.c
index e326b2bcff9867985d94720b4fbc2a8033568d88..943ef70fa601f7d4d8093183c9d1a6220a32c0dc 100644 (file)
--- a/drivers/serial/atmel_usart.c
+++ b/drivers/serial/atmel_usart.c
@@ -49,17 +49,26 @@ int serial_init(void)
 {
        atmel_usart3_t *usart = (atmel_usart3_t *)CONFIG_USART_BASE;
 
+       /*
+        * Just in case: drain transmitter register
+        * 1000us is enough for baudrate >= 9600
+        */
+       if (!(readl(&usart->csr) & USART3_BIT(TXEMPTY)))
+               __udelay(1000);
+
        writel(USART3_BIT(RSTRX) | USART3_BIT(RSTTX), &usart->cr);
 
        serial_setbrg();
 
-       writel(USART3_BIT(RXEN) | USART3_BIT(TXEN), &usart->cr);
        writel((USART3_BF(USART_MODE, USART3_USART_MODE_NORMAL)
                           | USART3_BF(USCLKS, USART3_USCLKS_MCK)
                           | USART3_BF(CHRL, USART3_CHRL_8)
                           | USART3_BF(PAR, USART3_PAR_NONE)
                           | USART3_BF(NBSTOP, USART3_NBSTOP_1)),
                           &usart->mr);
+       writel(USART3_BIT(RXEN) | USART3_BIT(TXEN), &usart->cr);
+       /* 100us is enough for the new settings to be settled */
+       __udelay(100);
 
        return 0;
 }