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Date:   Tue, 21 Nov 2023 00:28:03 +0100
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Subject: Re: [PATCH 2/2] serial: core: implement support for rs485-mux-gpios
Content-Language: en-US
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>
Cc:     devicetree@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Lukas Wunner <lukas@wunner.de>, linux-kernel@vger.kernel.org,
        linux-serial@vger.kernel.org
References: <20231120151056.148450-1-linux@rasmusvillemoes.dk>
 <20231120151056.148450-3-linux@rasmusvillemoes.dk>
From:   Lino Sanfilippo <l.sanfilippo@kunbus.com>
In-Reply-To: <20231120151056.148450-3-linux@rasmusvillemoes.dk>
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Hi,

On 20.11.23 16:10, Rasmus Villemoes wrote:
> Add code for handling a rs485-mux-gpio specified in device tree.
> 
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
>  drivers/tty/serial/serial_core.c | 35 ++++++++++++++++++++++++++++++--
>  include/linux/serial_core.h      |  1 +
>  2 files changed, 34 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index f1348a509552..410b17ea7444 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1402,14 +1402,20 @@ static void uart_set_rs485_termination(struct uart_port *port,
>  				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
>  }
>  
> +static void uart_set_rs485_mux(struct uart_port *port, const struct serial_rs485 *rs485)
> +{
> +	gpiod_set_value_cansleep(port->rs485_mux_gpio,
> +				 !!(rs485->flags & SER_RS485_ENABLED));
> +}
> +
>  static int uart_rs485_config(struct uart_port *port)
>  {
>  	struct serial_rs485 *rs485 = &port->rs485;
>  	unsigned long flags;
> -	int ret;
> +	int ret = 0;
>  
>  	if (!(rs485->flags & SER_RS485_ENABLED))
> -		return 0;
> +		goto out;
>  
>  	uart_sanitize_serial_rs485(port, rs485);
>  	uart_set_rs485_termination(port, rs485);
> @@ -1420,6 +1426,9 @@ static int uart_rs485_config(struct uart_port *port)
>  	if (ret)
>  		memset(rs485, 0, sizeof(*rs485));
>  
> +out:
> +	uart_set_rs485_mux(port, rs485);
> +
>  	return ret;
>  }
>  
> @@ -1457,6 +1466,14 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
>  		return ret;
>  	uart_sanitize_serial_rs485(port, &rs485);
>  	uart_set_rs485_termination(port, &rs485);
> +	/*
> +	 * To avoid glitches on the transmit enable pin, the mux must
> +	 * be set before calling the driver's ->rs485_config when
> +	 * disabling rs485 mode, but after when enabling rs485
> +	 * mode.
> +	 */
> +	if (!(rs485.flags & SER_RS485_ENABLED))
> +		uart_set_rs485_mux(port, &rs485);
>  
>  	uart_port_lock_irqsave(port, &flags);
>  	ret = port->rs485_config(port, &tty->termios, &rs485);
> @@ -1468,6 +1485,13 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
>  			port->ops->set_mctrl(port, port->mctrl);
>  	}
>  	uart_port_unlock_irqrestore(port, flags);
> +
> +	/*
> +	 * The ->rs485_config might have failed. Regardless, set the
> +	 * mux according to the port's effective rs485 config.
> +	 */
> +	uart_set_rs485_mux(port, &port->rs485);
> +
>  	if (ret)
>  		return ret;
>  
> @@ -3621,6 +3645,13 @@ int uart_get_rs485_mode(struct uart_port *port)
>  		return dev_err_probe(dev, PTR_ERR(desc), "Cannot get rs485-rx-during-tx-gpios\n");
>  	port->rs485_rx_during_tx_gpio = desc;
>  
> +	dflags = (rs485conf->flags & SER_RS485_ENABLED) ? GPIOD_OUT_HIGH : GPIOD_OUT_LOW;
> +	desc = devm_gpiod_get_optional(dev, "rs485-mux", dflags);
> +	if (IS_ERR(desc))
> +		return dev_err_probe(dev, PTR_ERR(port->rs485_mux_gpio),
> +				     "Cannot get rs485-mux-gpios\n");
> +	port->rs485_mux_gpio = desc;
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(uart_get_rs485_mode);
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 89f7b6c63598..943818209c49 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -584,6 +584,7 @@ struct uart_port {
>  	struct serial_rs485	rs485_supported;	/* Supported mask for serial_rs485 */
>  	struct gpio_desc	*rs485_term_gpio;	/* enable RS485 bus termination */
>  	struct gpio_desc	*rs485_rx_during_tx_gpio; /* Output GPIO that sets the state of RS485 RX during TX */
> +	struct gpio_desc	*rs485_mux_gpio;	/* gpio for selecting RS485 mode */
>  	struct serial_iso7816   iso7816;
>  	void			*private_data;		/* generic platform data pointer */
>  };

FWIW

Reviewed-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>

Regards,
Lino