linux-kernel - Re: [STLinux Kernel] [PATCH 4/8] serial: st-asc: (De)Register GPIOD and swap Pinctrl profiles

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Message-ID: <20170125112459.GF5680@griffinp-ThinkPad-X1-Carbon-2nd>
Date:   Wed, 25 Jan 2017 11:24:59 +0000
From:   Peter Griffin <peter.griffin@...aro.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     gregkh@...uxfoundation.org, jslaby@...e.com,
        linux-serial@...r.kernel.org, robh+dt@...nel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kernel@...inux.com
Subject: Re: [STLinux Kernel] [PATCH 4/8] serial: st-asc: (De)Register GPIOD
 and swap Pinctrl profiles

Hi Lee,

On Tue, 24 Jan 2017, Lee Jones wrote:

> When hardware flow-control is disabled, manual toggling of the UART's
> reset line (RTS) using userland applications (e.g. stty) is not
> possible, since the ASC IP does not provide this functionality in the
> same was as some other IPs do.  Thus, we have to do this manually.
> 
> This patch ensures that when HW flow-control is disabled the RTS/CTS
> lines are free to be registered via the GPIO API.  It also ensures
> any registered GPIO lines are unregistered when HW flow-control is
> requested, allowing the IP to control them automatically.

Apart from my comment in previous mail about switching the meaning of
default & manual-rts groupings. It seems like a neat solution.

Acked-by: Peter Griffin <peter.griffin@...aro.org>

> 
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  drivers/tty/serial/st-asc.c | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
> index 03801ed..2c4b5f5 100644
> --- a/drivers/tty/serial/st-asc.c
> +++ b/drivers/tty/serial/st-asc.c
> @@ -512,6 +512,8 @@ static void asc_set_termios(struct uart_port *port, struct ktermios *termios,
>  			    struct ktermios *old)
>  {
>  	struct asc_port *ascport = to_asc_port(port);
> +	struct device_node *np = port->dev->of_node;
> +	struct gpio_desc *gpiod;
>  	unsigned int baud;
>  	u32 ctrl_val;
>  	tcflag_t cflag;
> @@ -555,9 +557,32 @@ static void asc_set_termios(struct uart_port *port, struct ktermios *termios,
>  		ctrl_val |= ASC_CTL_PARITYODD;
>  
>  	/* hardware flow control */
> -	if ((cflag & CRTSCTS))
> +	if ((cflag & CRTSCTS)) {
>  		ctrl_val |= ASC_CTL_CTSENABLE;
>  
> +		/* If flow-control selected, stop handling RTS manually */
> +		if (ascport->rts) {
> +			devm_gpiod_put(port->dev, ascport->rts);
> +			ascport->rts = NULL;
> +
> +			pinctrl_select_state(ascport->pinctrl,
> +					     ascport->states[DEFAULT]);
> +		}
> +	} else {
> +		/* If flow-control disabled, it's safe to handle RTS manually */
> +		if (!ascport->rts && ascport->states[MANUAL_RTS]) {
> +			pinctrl_select_state(ascport->pinctrl,
> +					     ascport->states[MANUAL_RTS]);
> +
> +			gpiod =	devm_get_gpiod_from_child(port->dev, "rts",
> +							  &np->fwnode);
> +			if (!IS_ERR(gpiod)) {
> +				gpiod_direction_output(gpiod, 0);
> +				ascport->rts = gpiod;
> +			}
> +		}
> +	}
> +
>  	if ((baud < 19200) && !ascport->force_m1) {
>  		asc_out(port, ASC_BAUDRATE, (port->uartclk / (16 * baud)));
>  	} else {