linux-kernel - Re: [PATCH v7 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

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Date: Wed, 3 Jan 2024 13:10:33 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Lino Sanfilippo <l.sanfilippo@...bus.com>
cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, u.kleine-koenig@...gutronix.de, 
    shawnguo@...nel.org, s.hauer@...gutronix.de, mcoquelin.stm32@...il.com, 
    alexandre.torgue@...s.st.com, cniedermaier@...electronics.com, 
    hugo@...ovil.com, m.brock@...mierlo.com, 
    LKML <linux-kernel@...r.kernel.org>, 
    linux-serial <linux-serial@...r.kernel.org>, LinoSanfilippo@....de, 
    Lukas Wunner <lukas@...ner.de>, p.rosenberger@...bus.com, 
    stable@...r.kernel.org
Subject: Re: [PATCH v7 1/7] serial: Do not hold the port lock when setting
 rx-during-tx GPIO

On Wed, 3 Jan 2024, Lino Sanfilippo wrote:

> Both the imx and stm32 driver set the rx-during-tx GPIO in rs485_config().
> Since this function is called with the port lock held, this can be a
> problem in case that setting the GPIO line can sleep (e.g. if a GPIO
> expander is used which is connected via SPI or I2C).
> 
> Avoid this issue by moving the GPIO setting outside of the port lock into
> the serial core and thus making it a generic feature.
> 
> Also with commit c54d48543689 ("serial: stm32: Add support for rs485
> RX_DURING_TX output GPIO") the SER_RS485_RX_DURING_TX flag is only set if a
> rx-during-tx GPIO is _not_ available, which is wrong. Fix this, too.

This doesn't explain why it's wrong and I could figure it out myself 
either.

> Furthermore reset old GPIO settings in case that changing the RS485
> configuration failed.
> 
> Fixes: c54d48543689 ("serial: stm32: Add support for rs485 RX_DURING_TX output GPIO")
> Fixes: ca530cfa968c ("serial: imx: Add support for RS485 RX_DURING_TX output GPIO")
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: stable@...r.kernel.org
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/tty/serial/imx.c         |  4 ----
>  drivers/tty/serial/serial_core.c | 26 ++++++++++++++++++++++++--
>  drivers/tty/serial/stm32-usart.c |  8 ++------
>  3 files changed, 26 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 708b9852a575..9cffeb23112b 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1943,10 +1943,6 @@ static int imx_uart_rs485_config(struct uart_port *port, struct ktermios *termio
>  	    rs485conf->flags & SER_RS485_RX_DURING_TX)
>  		imx_uart_start_rx(port);
>  
> -	if (port->rs485_rx_during_tx_gpio)
> -		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> -					 !!(rs485conf->flags & SER_RS485_RX_DURING_TX));
> -
>  	return 0;
>  }
>  
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index f1348a509552..d155131f221d 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1402,6 +1402,16 @@ static void uart_set_rs485_termination(struct uart_port *port,
>  				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
>  }
>  
> +static void uart_set_rs485_rx_during_tx(struct uart_port *port,
> +					const struct serial_rs485 *rs485)
> +{
> +	if (!(rs485->flags & SER_RS485_ENABLED))
> +		return;
> +
> +	gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> +				 !!(rs485->flags & SER_RS485_RX_DURING_TX));
> +}
> +
>  static int uart_rs485_config(struct uart_port *port)
>  {
>  	struct serial_rs485 *rs485 = &port->rs485;
> @@ -1413,12 +1423,17 @@ static int uart_rs485_config(struct uart_port *port)
>  
>  	uart_sanitize_serial_rs485(port, rs485);
>  	uart_set_rs485_termination(port, rs485);
> +	uart_set_rs485_rx_during_tx(port, rs485);
>  
>  	uart_port_lock_irqsave(port, &flags);
>  	ret = port->rs485_config(port, NULL, rs485);
>  	uart_port_unlock_irqrestore(port, flags);
> -	if (ret)
> +	if (ret) {
>  		memset(rs485, 0, sizeof(*rs485));
> +		/* unset GPIOs */
> +		gpiod_set_value_cansleep(port->rs485_term_gpio, 0);
> +		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio, 0);
> +	}
>  
>  	return ret;
>  }
> @@ -1457,6 +1472,7 @@ 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);
> +	uart_set_rs485_rx_during_tx(port, &rs485);
>  
>  	uart_port_lock_irqsave(port, &flags);
>  	ret = port->rs485_config(port, &tty->termios, &rs485);
> @@ -1468,8 +1484,14 @@ 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);
> -	if (ret)
> +	if (ret) {
> +		/* restore old GPIO settings */
> +		gpiod_set_value_cansleep(port->rs485_term_gpio,
> +			!!(port->rs485.flags & SER_RS485_TERMINATE_BUS));
> +		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> +			!!(port->rs485.flags & SER_RS485_RX_DURING_TX));
>  		return ret;
> +	}
>  
>  	if (copy_to_user(rs485_user, &port->rs485, sizeof(port->rs485)))
>  		return -EFAULT;
> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
> index 3048620315d6..fc7fd40bca98 100644
> --- a/drivers/tty/serial/stm32-usart.c
> +++ b/drivers/tty/serial/stm32-usart.c
> @@ -226,12 +226,6 @@ static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *ter
>  
>  	stm32_usart_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
>  
> -	if (port->rs485_rx_during_tx_gpio)
> -		gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> -					 !!(rs485conf->flags & SER_RS485_RX_DURING_TX));
> -	else
> -		rs485conf->flags |= SER_RS485_RX_DURING_TX;
> -
>  	if (rs485conf->flags & SER_RS485_ENABLED) {
>  		cr1 = readl_relaxed(port->membase + ofs->cr1);
>  		cr3 = readl_relaxed(port->membase + ofs->cr3);
> @@ -256,6 +250,8 @@ static int stm32_usart_config_rs485(struct uart_port *port, struct ktermios *ter
>  
>  		writel_relaxed(cr3, port->membase + ofs->cr3);
>  		writel_relaxed(cr1, port->membase + ofs->cr1);
> +
> +		rs485conf->flags |= SER_RS485_RX_DURING_TX;

Is it really intentional to force this on even if user requests it not to 
be enabled (and after GPIO set value code used the value user provided)?

Other than that, this change looks fine.

-- 
 i.