[U-Boot] [PATCH] imx: serial: Wait for ongoing transmission to finish before serial reset

[Lothar Waßmann]

Hi,

On Tue,  3 Oct 2017 11:16:45 +0200 Lukasz Majewski wrote:
> It may happen that the MXC serial IP block is performing some ongoing
> transmission (started at e.g. board_init()) when the "initr_serial" is
> called.
> 
> As a result the serial port IP block is reset, so transmitted data is
> corrupted:
> 
> I2C:   ready
> DRAM:  1 GiB
> jSS('HH��SL_SDHC: 04 rev 0x0
> 
> This patch prevents from this situation, by waiting for transmission
> complete bit set (UART Status Register 2 (UARTx_USR2), bit TXDC):
> 
> I2C:   ready
> DRAM:  1 GiB
> ID:    unit type 0x4 rev 0x0
> 
> Signed-off-by: Lukasz Majewski <lukma at denx.de>
> ---
> 
>  drivers/serial/serial_mxc.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c
> index cce80a8..ef4eb12 100644
> --- a/drivers/serial/serial_mxc.c
> +++ b/drivers/serial/serial_mxc.c
> @@ -141,6 +141,13 @@ struct mxc_uart {
>  
>  static void _mxc_serial_init(struct mxc_uart *base)
>  {
> +	/*
> +	 * Wait for any ongoing transmission to finish - for example
> +	 * from pre-relocation enabled UART
> +	 */
> +	while (!(readl(&base->sr2) & USR2_TXDC))
> +		;
> +
>
Loops that poll for HW activated bits should always have a timeout.
Hardware will definitely break some day and deliver unexpected results.
Software should cope with this as best as it can!


Lothar Waßmann