Fixes and improvements for RS485 (RESEND)

[RESEND PATCH v4 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

Posted by Lino Sanfilippo 2 years, 1 month ago

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 an
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.

Since both setting the term and the rx-during-tx GPIO is done at the same
code place, move it into a common function.

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@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
---
 drivers/tty/serial/imx.c         |  4 ----
 drivers/tty/serial/serial_core.c | 15 +++++++++++----
 drivers/tty/serial/stm32-usart.c |  5 +----
 3 files changed, 12 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..ab766f48c172 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1392,14 +1392,21 @@ static void uart_sanitize_serial_rs485(struct uart_port *port, struct serial_rs4
 	memset(rs485->padding1, 0, sizeof(rs485->padding1));
 }
 
-static void uart_set_rs485_termination(struct uart_port *port,
-				       const struct serial_rs485 *rs485)
+/*
+ * Set optional RS485 GPIOs for bus termination and data reception during
+ * transmission. These GPIOs are controlled by the serial core independently
+ * from the UART driver.
+ */
+static void uart_set_rs485_gpios(struct uart_port *port,
+				 const struct serial_rs485 *rs485)
 {
 	if (!(rs485->flags & SER_RS485_ENABLED))
 		return;
 
 	gpiod_set_value_cansleep(port->rs485_term_gpio,
 				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
+	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)
@@ -1412,7 +1419,7 @@ static int uart_rs485_config(struct uart_port *port)
 		return 0;
 
 	uart_sanitize_serial_rs485(port, rs485);
-	uart_set_rs485_termination(port, rs485);
+	uart_set_rs485_gpios(port, rs485);
 
 	uart_port_lock_irqsave(port, &flags);
 	ret = port->rs485_config(port, NULL, rs485);
@@ -1456,7 +1463,7 @@ static int uart_set_rs485_config(struct tty_struct *tty, struct uart_port *port,
 	if (ret)
 		return ret;
 	uart_sanitize_serial_rs485(port, &rs485);
-	uart_set_rs485_termination(port, &rs485);
+	uart_set_rs485_gpios(port, &rs485);
 
 	uart_port_lock_irqsave(port, &flags);
 	ret = port->rs485_config(port, &tty->termios, &rs485);
diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 3048620315d6..ec9a72a5bea9 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -226,10 +226,7 @@ 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
+	if (!port->rs485_rx_during_tx_gpio)
 		rs485conf->flags |= SER_RS485_RX_DURING_TX;
 
 	if (rs485conf->flags & SER_RS485_ENABLED) {
-- 
2.42.0

Re: [RESEND PATCH v4 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

Posted by Lino Sanfilippo 2 years, 1 month ago

On 19.11.23 12:28, 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 an
> 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.
> 
> Since both setting the term and the rx-during-tx GPIO is done at the same
> code place, move it into a common function.

> -				       const struct serial_rs485 *rs485)
> +/*
> + * Set optional RS485 GPIOs for bus termination and data reception during
> + * transmission. These GPIOs are controlled by the serial core independently
> + * from the UART driver.
> + */
> +static void uart_set_rs485_gpios(struct uart_port *port,
> +				 const struct serial_rs485 *rs485)
>  {
>  	if (!(rs485->flags & SER_RS485_ENABLED))
>  		return;
>  
>  	gpiod_set_value_cansleep(port->rs485_term_gpio,
>  				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
> +	gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> +				 !!(rs485->flags & SER_RS485_RX_DURING_TX));
>  }
>  

Rasmus is about to add support for another RS485 related GPIO (see 
https://lore.kernel.org/all/20231120151056.148450-3-linux@rasmusvillemoes.dk/ )
which has to be configured both before and after port->rs485_config(). This
does not fit very well with the idea of handling all these GPIOs in
one function. 

So I would like to revise this patch and send an updated version in a v5
of this series in which the suggestion from Hugo
(see https://lore.kernel.org/all/20231011183656.5111ba32ec0c9d43171662a1@hugovil.com/)
is implemented to use separate functions for the GPIO configurations.

Regards,
Lino

Re: [RESEND PATCH v4 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO

Posted by Greg KH 2 years, 1 month ago

On Wed, Nov 22, 2023 at 12:55:49PM +0100, Lino Sanfilippo wrote:
> 
> 
> On 19.11.23 12:28, 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 an
> > 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.
> > 
> > Since both setting the term and the rx-during-tx GPIO is done at the same
> > code place, move it into a common function.
> 
> > -				       const struct serial_rs485 *rs485)
> > +/*
> > + * Set optional RS485 GPIOs for bus termination and data reception during
> > + * transmission. These GPIOs are controlled by the serial core independently
> > + * from the UART driver.
> > + */
> > +static void uart_set_rs485_gpios(struct uart_port *port,
> > +				 const struct serial_rs485 *rs485)
> >  {
> >  	if (!(rs485->flags & SER_RS485_ENABLED))
> >  		return;
> >  
> >  	gpiod_set_value_cansleep(port->rs485_term_gpio,
> >  				 !!(rs485->flags & SER_RS485_TERMINATE_BUS));
> > +	gpiod_set_value_cansleep(port->rs485_rx_during_tx_gpio,
> > +				 !!(rs485->flags & SER_RS485_RX_DURING_TX));
> >  }
> >  
> 
> Rasmus is about to add support for another RS485 related GPIO (see 
> https://lore.kernel.org/all/20231120151056.148450-3-linux@rasmusvillemoes.dk/ )
> which has to be configured both before and after port->rs485_config(). This
> does not fit very well with the idea of handling all these GPIOs in
> one function. 
> 
> So I would like to revise this patch and send an updated version in a v5
> of this series in which the suggestion from Hugo
> (see https://lore.kernel.org/all/20231011183656.5111ba32ec0c9d43171662a1@hugovil.com/)
> is implemented to use separate functions for the GPIO configurations.
> 

I'll drop this, thanks for letting me know.

There are WAY too many different "enable 485 in this way" patches that
are all conflicting with each other.  Can you all decide on a common way
to handle this, otherwise none of these are going to be acceptable :(

thanks,

greg k-h

[RESEND PATCH v4 1/7] serial: Do not hold the port lock when setting rx-during-tx GPIO
[RESEND PATCH v4 2/7] serial: core: set missing supported flag for RX during TX GPIO
[RESEND PATCH v4 3/7] serial: core: fix sanitizing check for RTS settings
[RESEND PATCH v4 4/7] serial: core: make sure RS485 cannot be enabled when it is not supported
[RESEND PATCH v4 5/7] serial: core, imx: do not set RS485 enabled if it is not supported
[RESEND PATCH v4 6/7] serial: omap: do not override settings for RS485 support
[RESEND PATCH v4 7/7] serial: 8250_exar: Set missing rs485_supported flag