linux-kernel - Re: [PATCH 2/8] serial: core, 8250: set RS485 termination gpio in serial core

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Date:   Sat, 25 Jun 2022 13:40:16 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        vz@...ia.com, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, lukas@...ner.de,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH 2/8] serial: core, 8250: set RS485 termination gpio in
 serial core

On Wed, 22 Jun 2022, Lino Sanfilippo wrote:

> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
> 
> In serial8250_em485_config() the termination GPIO is set with the uart_port
> spinlock held. This is an issue if setting the GPIO line can sleep (e.g.
> since the concerning GPIO expander is connected via SPI or I2C).
> 
> Fix this by setting the termination line outside of the uart_port spinlock
> in the serial core.
> 
> This also makes setting the termination GPIO generic for all uart drivers.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/tty/serial/8250/8250_port.c |  3 ---
>  drivers/tty/serial/serial_core.c    | 12 ++++++++++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 3e3d784aa628..5245c179cc51 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -675,9 +675,6 @@ int serial8250_em485_config(struct uart_port *port, struct serial_rs485 *rs485)
>  		rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
>  	}
>  
> -	gpiod_set_value(port->rs485_term_gpio,
> -			rs485->flags & SER_RS485_TERMINATE_BUS);
> -
>  	/*
>  	 * Both serial8250_em485_init() and serial8250_em485_destroy()
>  	 * are idempotent.
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 015f4e1da647..b387376e6fa2 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1352,12 +1352,23 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
>  	memset(rs485->padding, 0, sizeof(rs485->padding));
>  }
>  
> +static void uart_set_rs485_termination(struct uart_port *port,
> +				       const struct serial_rs485 *rs485)
> +{
> +	if (!port->rs485_term_gpio || !(rs485->flags & SER_RS485_ENABLED))
> +		return;
> +
> +	gpiod_set_value_cansleep(port->rs485_term_gpio,
> +				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
> +}
> +
>  int uart_rs485_config(struct uart_port *port)
>  {
>  	struct serial_rs485 *rs485 = &port->rs485;
>  	int ret;
>  
>  	uart_sanitize_serial_rs485(port, rs485);
> +	uart_set_rs485_termination(port, rs485);
>  
>  	ret = port->rs485_config(port, rs485);
>  	if (ret)
> @@ -1400,6 +1411,7 @@ static int uart_set_rs485_config(struct uart_port *port,
>  	if (ret)
>  		return ret;
>  	uart_sanitize_serial_rs485(port, &rs485);
> +	uart_set_rs485_termination(port, &rs485);
>  
>  	spin_lock_irqsave(&port->lock, flags);
>  	ret = port->rs485_config(port, &rs485);

When port->rs485_config(port, &rs485) returns non-zero, the input got 
partially applied?


-- 
 i.