[PATCH] serial: mxc: Wait until TX FIFO is not full

[Fabio Estevam <festevam@gmail.com>]

From: Fabio Estevam <festevam@denx.de>

Tim Harvey reported the console garbage on imx6 since
commit c7878a0483c5 ("serial: mxc: have putc use the TXFIFO").

Do as suggested by Pali Rohár where the the driver should
not return -EAGAIN when the TX FIFO  is full.

It should keep waiting until the TX FIFO is no longer full.

This also aligns with the implementation of the imx serial driver
in the kernel:

static void imx_uart_console_putchar(struct uart_port *port, unsigned char ch)
{
    struct imx_port *sport = (struct imx_port *)port;

    while (imx_uart_readl(sport, imx_uart_uts_reg(sport)) & UTS_TXFULL)
        barrier();

    imx_uart_writel(sport, ch, URTX0);
}

Fixes: c7878a0483c5 ("serial: mxc: have putc use the TXFIFO")
Reported-by: Tim Harvey <tharvey@gateworks.com>
Suggested-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Fabio Estevam <festevam@denx.de>
---
 drivers/serial/serial_mxc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
index 4cf79c1ca24f..332219fa87fc 100644
--- a/drivers/serial/serial_mxc.c
+++ b/drivers/serial/serial_mxc.c
@@ -311,8 +311,8 @@ static int mxc_serial_putc(struct udevice *dev, const char ch)
 	struct mxc_serial_plat *plat = dev_get_plat(dev);
 	struct mxc_uart *const uart = plat->reg;
 
-	if (readl(&uart->ts) & UTS_TXFULL)
-		return -EAGAIN;
+	while (readl(&uart->ts) & UTS_TXFULL)
+		barrier();
 
 	writel(ch, &uart->txd);
 
-- 
2.25.1