[PATCH] serial: ns16550: Wait in debug_uart_init until tx buffer is empty

[Stefan Roese]

On 23.06.22 14:13, Pali Rohár wrote:
> Commit d293759d55cc ("serial: ns16550: Add support for
> SPL_DEBUG_UART_BASE") fixed support for setting correct early debug UART
> base address in SPL.
> 
> But after this commit, output from Marvell A385 BootROM is truncated or
> lost and not fully present on serial console.
> 
> Debugging this issue showed that BootROM just put bytes into UART HW output
> buffer and does not wait until UART HW transmit all characters. U-Boot
> ns16550 early debug is initialized very early and during its initialization
> is resetting UART HW and flushing remaining transmit buffer (which still
> contains BootROM output).
> 
> Fix this issue by waiting in init function prior resetting UART HW until
> TxEmpty bit in UART Line Status Register is set. TxEmpty is set when all
> remaining bytes from HW buffer are transmitted.
> 
> Signed-off-by: Pali Rohár <pali at kernel.org>

Just checking, do you need a "Fixes" tag as well here?

> ---
>   drivers/serial/ns16550.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/serial/ns16550.c b/drivers/serial/ns16550.c
> index 78bfe6281ce3..13418004e2b0 100644
> --- a/drivers/serial/ns16550.c
> +++ b/drivers/serial/ns16550.c
> @@ -328,6 +328,8 @@ static inline void _debug_uart_init(void)
>   	struct ns16550 *com_port = (struct ns16550 *)CONFIG_VAL(DEBUG_UART_BASE);
>   	int baud_divisor;
>   
> +	while (!(serial_din(&com_port->lsr) & UART_LSR_TEMT));

I personally prefer the ";" in a separate line instead. Not sure what
the official coding style mentions to such constructs.

Anyways:

Reviewed-by: Stefan Roese <sr at denx.de>

Thanks,
Stefan