Re: [PATCH 2/2] serial: imx: Fix the CTS_B polarity in RS485 mode

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On Mon, Jan 30, 2017 at 09:12:12AM -0200, Fabio Estevam wrote:
> When userspace passes the SER_RS485_RTS_ON_SEND flag it means that the
> CTS_B pin should go to logic level high before the transmission begins.
> 
> CTS_B goes to logic level high when both CTSC and CTS bits are cleared.
> 
> When userspace passes the SER_RS485_RTS_AFTER_SEND flag it means that the
> CTS_B pin should go to logic level low after the transmission finishes.
> 
> CTS_B goes to logic level low when CTSC bit is cleared and CTS bit is set.
> 
> So fix the CTS_B polarity logic.
> 
> Signed-off-by: Fabio Estevam <fabio.estevam@xxxxxxx>
> ---
> I do not have access to a board that uses CTS_B pin connected to a 
> RS485 transceiver.
> 
> I have tested with a scope that the polarity of CTS_B is correct when
> this patch is applied.
> 
>  drivers/tty/serial/imx.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 29dd57c..e3e152c 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -336,15 +336,15 @@ static void imx_port_ucrs_restore(struct uart_port *port,
>  
>  static void imx_port_rts_active(struct imx_port *sport, unsigned long *ucr2)
>  {
> -	*ucr2 &= ~UCR2_CTSC;
> -	*ucr2 |= UCR2_CTS;
> +	*ucr2 &= ~(UCR2_CTSC | UCR2_CTS);
>  
>  	mctrl_gpio_set(sport->gpios, sport->port.mctrl | TIOCM_RTS);
>  }
>  
>  static void imx_port_rts_inactive(struct imx_port *sport, unsigned long *ucr2)
>  {
> -	*ucr2 &= ~(UCR2_CTSC | UCR2_CTS);
> +	*ucr2 &= ~UCR2_CTSC;
> +	*ucr2 |= UCR2_CTS;
>  
>  	mctrl_gpio_set(sport->gpios, sport->port.mctrl & ~TIOCM_RTS);
>  }
> -- 
> 2.7.4
>

Tested on a board with the RS-485 transceivers TE signal connected to
the CTS_B pin of the i.MX6Q. Works fine and is much more consistent with
the naming of the flags in struct serial_rs485!

Tested-by: Clemens Gruber <clemens.gruber@xxxxxxxxxxxx>

Regards,
Clemens
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