On Thursday 12 January 2023 18:19:50 Loic Poulain wrote:
> The u-boot console may show some corrupted characters when
> printing in board_init() due to reset or baudrate change
> of the UART (probe) before the TX FIFO has been completely
> drained.
>
> To fix this issue, and in case UART is still running, we now
> try to flush the FIFO before proceeding to UART reinitialization.
> For this we're waiting for Transmitter Complete bit, indicating
> that the FIFO and the shift register are empty.
>
> flushing has a 4ms timeout guard, which is normally more than
> enough to consume the FIFO @ low baudrate (9600bps).
>
> Signed-off-by: Loic Poulain <loic.poul...@linaro.org>
> Tested-by: Lothar Waßmann <l...@karo-electronics.de>
Acked-by: Pali Rohár <p...@kernel.org>
> ---
> v2: Add this commit to the series
> v3: Fix typo & reordering commits for good bisectabilit
> v4: Wait for transfer completion before baudrate change as well
>
> drivers/serial/serial_mxc.c | 26 +++++++++++++++++++++++++-
> 1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
> index 82c0d84628..9e5b987994 100644
> --- a/drivers/serial/serial_mxc.c
> +++ b/drivers/serial/serial_mxc.c
> @@ -13,6 +13,7 @@
> #include <dm/platform_data/serial_mxc.h>
> #include <serial.h>
> #include <linux/compiler.h>
> +#include <linux/delay.h>
>
> /* UART Control Register Bit Fields.*/
> #define URXD_CHARRDY (1<<15)
> @@ -144,8 +145,22 @@ struct mxc_uart {
> u32 ts;
> };
>
> +static void _mxc_serial_flush(struct mxc_uart *base)
> +{
> + unsigned int timeout = 4000;
> +
> + if (!(readl(&base->cr1) & UCR1_UARTEN) ||
> + !(readl(&base->cr2) & UCR2_TXEN))
> + return;
> +
> + while (!(readl(&base->sr2) & USR2_TXDC) && --timeout)
> + udelay(1);
> +}
> +
> static void _mxc_serial_init(struct mxc_uart *base, int use_dte)
> {
> + _mxc_serial_flush(base);
> +
> writel(0, &base->cr1);
> writel(0, &base->cr2);
>
> @@ -169,6 +184,8 @@ static void _mxc_serial_setbrg(struct mxc_uart *base,
> unsigned long clk,
> {
> u32 tmp;
>
> + _mxc_serial_flush(base);
> +
> tmp = RFDIV << UFCR_RFDIV_SHF;
> if (use_dte)
> tmp |= UFCR_DCEDTE;
> @@ -252,10 +269,17 @@ static int mxc_serial_init(void)
> return 0;
> }
>
> +static int mxc_serial_stop(void)
> +{
> + _mxc_serial_flush(mxc_base);
> +
> + return 0;
> +}
> +
> static struct serial_device mxc_serial_drv = {
> .name = "mxc_serial",
> .start = mxc_serial_init,
> - .stop = NULL,
> + .stop = mxc_serial_stop,
> .setbrg = mxc_serial_setbrg,
> .putc = mxc_serial_putc,
> .puts = default_serial_puts,
> --
> 2.34.1
>
