linux-kernel - Re: [PATCH v2 08/11] serial: sh-sci: Correct pin initialization on (H)SCIF

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Date:	Fri, 29 Apr 2016 08:59:37 -0700
From:	Peter Hurley <peter@...leysoftware.com>
To:	Geert Uytterhoeven <geert+renesas@...der.be>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	linux-serial@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
	linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 08/11] serial: sh-sci: Correct pin initialization on
 (H)SCIF

On 04/29/2016 05:58 AM, Geert Uytterhoeven wrote:
> Correct pin initialization on (H)SCIF:
>   - RTS must be deasserted (it's active low),
>   - SCK must be an input, as it may be used as the optional external
>     clock input.
> 
> Initial pin configuration must always be done:
>   - Regardless of the presence of dedicated RTS and CTS pins: if the
>     register exists, the RTS/CTS bits exist, too,
>   - Regardless of hardware flow control being enabled or not: RTS must
>     be deasserted.

This is always setting RTS active; why?

Normally you want to program RTS only in response to ->set_mctrl()
from serial core.  For example, this will set RTS active even though
baud might be set to B0.


> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> v2:
>   - New.
> ---
>  drivers/tty/serial/sh-sci.c | 23 ++++++++---------------
>  1 file changed, 8 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
> index ce7bd165929ea078..c46999f20917964e 100644
> --- a/drivers/tty/serial/sh-sci.c
> +++ b/drivers/tty/serial/sh-sci.c
> @@ -712,21 +712,14 @@ static void sci_init_pins(struct uart_port *port, unsigned int cflag)
>  		return;
>  	}
>  
> -	/*
> -	 * For the generic path SCSPTR is necessary. Bail out if that's
> -	 * unavailable, too.
> -	 */
> -	if (!sci_getreg(port, SCSPTR)->size)
> -		return;
> -
> -	if ((s->cfg->capabilities & SCIx_HAVE_RTSCTS) &&
> -	    ((!(cflag & CRTSCTS)))) {
> -		unsigned short status;
> -
> -		status = serial_port_in(port, SCSPTR);
> -		status &= ~SCSPTR_CTSIO;
> -		status |= SCSPTR_RTSIO;
> -		serial_port_out(port, SCSPTR, status); /* Set RTS = 1 */
> +	if (sci_getreg(port, SCSPTR)->size) {
> +		u16 status = serial_port_in(port, SCSPTR);
> +
> +		/* RTS# is output, driven 1 */
> +		status |= SCSPTR_RTSIO | SCSPTR_RTSDT;
> +		/* CTS# and SCK are inputs */
> +		status &= ~(SCSPTR_CTSIO | SCSPTR_SCKIO);
> +		serial_port_out(port, SCSPTR, status);
>  	}
>  }
>  
>