Move RS485 implementation from drivers to serial core (v4 RESEND)

Move RS485 implementation from drivers to serial core (v4 RESEND)

[Lino Sanfilippo]

This patch series is an attempt to simplify rs485 implementation in drivers
by moving the following tasks out of the drivers into the serial core:

- ensure sane RTS settings: in case of an invalid configuration (both RTS
  after send and RTS on send set or both unset) enable RTS on send and
  disable RTS after send

- nullify the padding field of the serial_rs485 struct before it is
  returned to userspace

- copy the configuration stored in the serial_rs485 struct to the port
  configuration if setting the configuration in the driver was successfull

- limit the RTS delay to 100ms


Redundant code has been removed from the following drivers for now:

- atmel
- fsl_lpuart
- amba
- imx
- max310x
- omap-serial
- sc16is7xx
- stm32-usart

The code has been tested with the amba pl011 driver. This series applies
against Gregs tty-testing branch.

Changes in v2:
- use a makro for max RTS delays and comment it (as requested by Jiri)
- add a comment concerning the memset of a structures padding field - correct
  typos in the commit message (found by Uwe) 
- rephrase all commit messages to make more clear that function
  uart_set_rs485_config() has been extended by checks and other functionalities
  (as requested by Uwe)

Changes in v3:
- add warning messages if the serial core corrects RS485 values (as requested by
  Lukas Wunner)
- dont expose the macro for max RTS delays to userspace (as requested by Greg)

Changes in v4:
- use ratelimit warning messages and also print device, uart port name and line
  (as requested by Jiri)

[PATCH v4 RESEND 1/9] serial: core: move RS485 configuration tasks from drivers into core

[Lino Sanfilippo]

Several drivers that support setting the RS485 configuration via userspace
implement one or more of the following tasks:

- in case of an invalid RTS configuration (both RTS after send and RTS on
  send set or both unset) fall back to enable RTS on send and disable RTS
  after send

- nullify the padding field of the returned serial_rs485 struct

- copy the configuration into the uart port struct

- limit RTS delays to 100 ms

Move these tasks into the serial core to make them generic and to provide
a consistent behaviour among all drivers.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/serial_core.c | 33 ++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 6a8963caf954..108b389e6e12 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -42,6 +42,11 @@ static struct lock_class_key port_lock_key;
 
 #define HIGH_BITS_OFFSET	((sizeof(long)-sizeof(int))*8)
 
+/*
+ * Max time with active RTS before/after data is sent.
+ */
+#define RS485_MAX_RTS_DELAY	100 /* msecs */
+
 static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
 					struct ktermios *old_termios);
 static void uart_wait_until_sent(struct tty_struct *tty, int timeout);
@@ -1296,8 +1301,36 @@ static int uart_set_rs485_config(struct uart_port *port,
 	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
 		return -EFAULT;
 
+	/* pick sane settings if the user hasn't */
+	if (!(rs485.flags & SER_RS485_RTS_ON_SEND) ==
+	    !(rs485.flags & SER_RS485_RTS_AFTER_SEND)) {
+		dev_warn_ratelimited(port->dev,
+			"%s (%d): invalid RTS setting, using RTS_ON_SEND instead\n",
+			port->name, port->line);
+		rs485.flags |= SER_RS485_RTS_ON_SEND;
+		rs485.flags &= ~SER_RS485_RTS_AFTER_SEND;
+	}
+
+	if (rs485.delay_rts_before_send > RS485_MAX_RTS_DELAY) {
+		rs485.delay_rts_before_send = RS485_MAX_RTS_DELAY;
+		dev_warn_ratelimited(port->dev,
+			"%s (%d): RTS delay before sending clamped to %u ms\n",
+			port->name, port->line, rs485.delay_rts_before_send);
+	}
+
+	if (rs485.delay_rts_after_send > RS485_MAX_RTS_DELAY) {
+		rs485.delay_rts_after_send = RS485_MAX_RTS_DELAY;
+		dev_warn_ratelimited(port->dev,
+			"%s (%d): RTS delay after sending clamped to %u ms\n",
+			port->name, port->line, rs485.delay_rts_after_send);
+	}
+	/* Return clean padding area to userspace */
+	memset(rs485.padding, 0, sizeof(rs485.padding));
+
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, &rs485);
+	if (!ret)
+		port->rs485 = rs485;
 	spin_unlock_irqrestore(&port->lock, flags);
 	if (ret)
 		return ret;

base-commit: 3123109284176b1532874591f7c81f3837bbdc17
-- 
2.35.1

[PATCH v4 RESEND 2/9] serial: amba-pl011: remove redundant code in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already

- ensures that only one of both options RTS on send or RTS after send is
  set

- nullifies the padding field of the passed serial_rs485 struct

- clamps the RTS delays

- assigns the passed serial_rs485 struct to the uart port

So remove these tasks from the code of the drivers rs485_config() function
to avoid redundancy.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/amba-pl011.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 51ecb050ae40..de2c4dc6257e 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2170,25 +2170,11 @@ static int pl011_rs485_config(struct uart_port *port,
 	struct uart_amba_port *uap =
 		container_of(port, struct uart_amba_port, port);
 
-	/* pick sane settings if the user hasn't */
-	if (!(rs485->flags & SER_RS485_RTS_ON_SEND) ==
-	    !(rs485->flags & SER_RS485_RTS_AFTER_SEND)) {
-		rs485->flags |= SER_RS485_RTS_ON_SEND;
-		rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
-	}
-	/* clamp the delays to [0, 100ms] */
-	rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
-	rs485->delay_rts_after_send = min(rs485->delay_rts_after_send, 100U);
-	memset(rs485->padding, 0, sizeof(rs485->padding));
-
 	if (port->rs485.flags & SER_RS485_ENABLED)
 		pl011_rs485_tx_stop(uap);
 
-	/* Set new configuration */
-	port->rs485 = *rs485;
-
 	/* Make sure auto RTS is disabled */
-	if (port->rs485.flags & SER_RS485_ENABLED) {
+	if (rs485->flags & SER_RS485_ENABLED) {
 		u32 cr = pl011_read(uap, REG_CR);
 
 		cr &= ~UART011_CR_RTSEN;
-- 
2.35.1

[PATCH v4 RESEND 3/9] serial: stm32: remove redundant code in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already ensures that only one of
both options RTS on send or RTS after send is set. It also assigns the
passed serial_rs485 struct to the uart port.

So remove the check and the assignment from the drivers rs485_config()
function to avoid redundancy.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/stm32-usart.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 87b5cd4c9743..f886976daef6 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -107,8 +107,6 @@ static int stm32_usart_config_rs485(struct uart_port *port,
 
 	stm32_usart_clr_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
 
-	port->rs485 = *rs485conf;
-
 	rs485conf->flags |= SER_RS485_RX_DURING_TX;
 
 	if (rs485conf->flags & SER_RS485_ENABLED) {
@@ -128,13 +126,10 @@ static int stm32_usart_config_rs485(struct uart_port *port,
 					     rs485conf->delay_rts_after_send,
 					     baud);
 
-		if (rs485conf->flags & SER_RS485_RTS_ON_SEND) {
+		if (rs485conf->flags & SER_RS485_RTS_ON_SEND)
 			cr3 &= ~USART_CR3_DEP;
-			rs485conf->flags &= ~SER_RS485_RTS_AFTER_SEND;
-		} else {
+		else
 			cr3 |= USART_CR3_DEP;
-			rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
-		}
 
 		writel_relaxed(cr3, port->membase + ofs->cr3);
 		writel_relaxed(cr1, port->membase + ofs->cr1);
-- 
2.35.1

[PATCH v4 RESEND 4/9] serial: sc16is7xx: remove redundant check in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already ensures that only one of
both options RTS on send or RTS after send is set.

So remove this check from the drivers rs485_config() function to avoid
redundancy.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/sc16is7xx.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index e857fb61efbf..bb939d2877db 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1134,16 +1134,6 @@ static int sc16is7xx_config_rs485(struct uart_port *port,
 	struct sc16is7xx_one *one = to_sc16is7xx_one(port, port);
 
 	if (rs485->flags & SER_RS485_ENABLED) {
-		bool rts_during_rx, rts_during_tx;
-
-		rts_during_rx = rs485->flags & SER_RS485_RTS_AFTER_SEND;
-		rts_during_tx = rs485->flags & SER_RS485_RTS_ON_SEND;
-
-		if (rts_during_rx == rts_during_tx)
-			dev_err(port->dev,
-				"unsupported RTS signalling on_send:%d after_send:%d - exactly one of RS485 RTS flags should be set\n",
-				rts_during_tx, rts_during_rx);
-
 		/*
 		 * RTS signal is handled by HW, it's timing can't be influenced.
 		 * However, it's sometimes useful to delay TX even without RTS
-- 
2.35.1

[PATCH v4 RESEND 5/9] serial: omap: remove redundant code in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already clamps the RTS delays.
It also assigns the passed serial_rs485 struct to the uart port.

So remove these tasks from the drivers rs485_config() function to avoid
redundancy.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/omap-serial.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
index 8d5ffa196097..46f4d4cacb6e 100644
--- a/drivers/tty/serial/omap-serial.c
+++ b/drivers/tty/serial/omap-serial.c
@@ -1336,18 +1336,11 @@ serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
 	up->ier = 0;
 	serial_out(up, UART_IER, 0);
 
-	/* Clamp the delays to [0, 100ms] */
-	rs485->delay_rts_before_send = min(rs485->delay_rts_before_send, 100U);
-	rs485->delay_rts_after_send  = min(rs485->delay_rts_after_send, 100U);
-
-	/* store new config */
-	port->rs485 = *rs485;
-
 	if (up->rts_gpiod) {
 		/* enable / disable rts */
-		val = (port->rs485.flags & SER_RS485_ENABLED) ?
+		val = (rs485->flags & SER_RS485_ENABLED) ?
 			SER_RS485_RTS_AFTER_SEND : SER_RS485_RTS_ON_SEND;
-		val = (port->rs485.flags & val) ? 1 : 0;
+		val = (rs485->flags & val) ? 1 : 0;
 		gpiod_set_value(up->rts_gpiod, val);
 	}
 
@@ -1358,7 +1351,7 @@ serial_omap_config_rs485(struct uart_port *port, struct serial_rs485 *rs485)
 	/* If RS-485 is disabled, make sure the THR interrupt is fired when
 	 * TX FIFO is below the trigger level.
 	 */
-	if (!(port->rs485.flags & SER_RS485_ENABLED) &&
+	if (!(rs485->flags & SER_RS485_ENABLED) &&
 	    (up->scr & OMAP_UART_SCR_TX_EMPTY)) {
 		up->scr &= ~OMAP_UART_SCR_TX_EMPTY;
 		serial_out(up, UART_OMAP_SCR, up->scr);
-- 
2.35.1

[PATCH v4 RESEND 6/9] serial: max310: remove redundant memset in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already nullifies the padding
field of the passed serial_rs485 struct before returning it to userspace.

Doing the same in the drivers rs485_config() function is redundant, so
remove the concerning memset in this function.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/max310x.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/tty/serial/max310x.c b/drivers/tty/serial/max310x.c
index 3112b4a05448..a0b6ea52d133 100644
--- a/drivers/tty/serial/max310x.c
+++ b/drivers/tty/serial/max310x.c
@@ -1037,7 +1037,6 @@ static int max310x_rs485_config(struct uart_port *port,
 
 	rs485->flags &= SER_RS485_RTS_ON_SEND | SER_RS485_RX_DURING_TX |
 			SER_RS485_ENABLED;
-	memset(rs485->padding, 0, sizeof(rs485->padding));
 	port->rs485 = *rs485;
 
 	schedule_work(&one->rs_work);
-- 
2.35.1

[PATCH v4 RESEND 7/9] serial: imx: remove redundant assignment in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already assigns the passed
serial_rs485 struct to the uart port.

So remove the assignment in the drivers rs485_config() function to avoid
reduncancy.

Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/imx.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index fd38e6ed4fda..e934880febe8 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1937,8 +1937,6 @@ static int imx_uart_rs485_config(struct uart_port *port,
 	    rs485conf->flags & SER_RS485_RX_DURING_TX)
 		imx_uart_start_rx(port);
 
-	port->rs485 = *rs485conf;
-
 	return 0;
 }
 
-- 
2.35.1

[PATCH v4 RESEND 8/9] serial: fsl_lpuart: remove redundant code in rs485_config functions

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already ensures that only one of
both options RTS on send or RTS after send is set. It also assigns the
passed serial_rs485 struct to the uart port.

So remove the check and the assignment from the drivers rs485_config()
function to avoid redundancy.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/fsl_lpuart.c | 32 --------------------------------
 1 file changed, 32 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 87789872f400..8fea7fd915d2 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1377,19 +1377,6 @@ static int lpuart_config_rs485(struct uart_port *port,
 		/* Enable auto RS-485 RTS mode */
 		modem |= UARTMODEM_TXRTSE;
 
-		/*
-		 * RTS needs to be logic HIGH either during transfer _or_ after
-		 * transfer, other variants are not supported by the hardware.
-		 */
-
-		if (!(rs485->flags & (SER_RS485_RTS_ON_SEND |
-				SER_RS485_RTS_AFTER_SEND)))
-			rs485->flags |= SER_RS485_RTS_ON_SEND;
-
-		if (rs485->flags & SER_RS485_RTS_ON_SEND &&
-				rs485->flags & SER_RS485_RTS_AFTER_SEND)
-			rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
-
 		/*
 		 * The hardware defaults to RTS logic HIGH while transfer.
 		 * Switch polarity in case RTS shall be logic HIGH
@@ -1402,9 +1389,6 @@ static int lpuart_config_rs485(struct uart_port *port,
 			modem |= UARTMODEM_TXRTSPOL;
 	}
 
-	/* Store the new configuration */
-	sport->port.rs485 = *rs485;
-
 	writeb(modem, sport->port.membase + UARTMODEM);
 	return 0;
 }
@@ -1428,19 +1412,6 @@ static int lpuart32_config_rs485(struct uart_port *port,
 		/* Enable auto RS-485 RTS mode */
 		modem |= UARTMODEM_TXRTSE;
 
-		/*
-		 * RTS needs to be logic HIGH either during transfer _or_ after
-		 * transfer, other variants are not supported by the hardware.
-		 */
-
-		if (!(rs485->flags & (SER_RS485_RTS_ON_SEND |
-				SER_RS485_RTS_AFTER_SEND)))
-			rs485->flags |= SER_RS485_RTS_ON_SEND;
-
-		if (rs485->flags & SER_RS485_RTS_ON_SEND &&
-				rs485->flags & SER_RS485_RTS_AFTER_SEND)
-			rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
-
 		/*
 		 * The hardware defaults to RTS logic HIGH while transfer.
 		 * Switch polarity in case RTS shall be logic HIGH
@@ -1453,9 +1424,6 @@ static int lpuart32_config_rs485(struct uart_port *port,
 			modem |= UARTMODEM_TXRTSPOL;
 	}
 
-	/* Store the new configuration */
-	sport->port.rs485 = *rs485;
-
 	lpuart32_write(&sport->port, modem, UARTMODIR);
 	return 0;
 }
-- 
2.35.1

[PATCH v4 RESEND 9/9] serial: atmel: remove redundant assignment in rs485_config

[Lino Sanfilippo]

In uart_set_rs485_config() the serial core already assigns the passed
serial_rs485 struct to the uart port.

So remove the assignment from the drivers rs485_config() function to avoid
redundancy.

Acked-by: Richard Genoud <richard.genoud@gmail.com>
Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
---
 drivers/tty/serial/atmel_serial.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 3a45e4fc7993..dd1c7e4bd1c9 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -299,11 +299,9 @@ static int atmel_config_rs485(struct uart_port *port,
 	/* Resetting serial mode to RS232 (0x0) */
 	mode &= ~ATMEL_US_USMODE;
 
-	port->rs485 = *rs485conf;
-
 	if (rs485conf->flags & SER_RS485_ENABLED) {
 		dev_dbg(port->dev, "Setting UART to RS485\n");
-		if (port->rs485.flags & SER_RS485_RX_DURING_TX)
+		if (rs485conf->flags & SER_RS485_RX_DURING_TX)
 			atmel_port->tx_done_mask = ATMEL_US_TXRDY;
 		else
 			atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
-- 
2.35.1

Re: [PATCH v4 RESEND 9/9] serial: atmel: remove redundant assignment in rs485_config

[Claudiu.Beznea]

On 10.04.2022 13:46, Lino Sanfilippo wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> In uart_set_rs485_config() the serial core already assigns the passed
> serial_rs485 struct to the uart port.
> 
> So remove the assignment from the drivers rs485_config() function to avoid
> redundancy.
> 
> Acked-by: Richard Genoud <richard.genoud@gmail.com>
> Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>

Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>


> ---
>  drivers/tty/serial/atmel_serial.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 3a45e4fc7993..dd1c7e4bd1c9 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -299,11 +299,9 @@ static int atmel_config_rs485(struct uart_port *port,
>         /* Resetting serial mode to RS232 (0x0) */
>         mode &= ~ATMEL_US_USMODE;
> 
> -       port->rs485 = *rs485conf;
> -
>         if (rs485conf->flags & SER_RS485_ENABLED) {
>                 dev_dbg(port->dev, "Setting UART to RS485\n");
> -               if (port->rs485.flags & SER_RS485_RX_DURING_TX)
> +               if (rs485conf->flags & SER_RS485_RX_DURING_TX)
>                         atmel_port->tx_done_mask = ATMEL_US_TXRDY;
>                 else
>                         atmel_port->tx_done_mask = ATMEL_US_TXEMPTY;
> --
> 2.35.1
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: Move RS485 implementation from drivers to serial core (v4 RESEND)

[Lukas Wunner]

On Sun, Apr 10, 2022 at 12:46:33PM +0200, Lino Sanfilippo wrote:
> This patch series is an attempt to simplify rs485 implementation in drivers
> by moving the following tasks out of the drivers into the serial core:
> 
> - ensure sane RTS settings: in case of an invalid configuration (both RTS
>   after send and RTS on send set or both unset) enable RTS on send and
>   disable RTS after send
[...]
> Redundant code has been removed from the following drivers for now:
> 
> - atmel
> - fsl_lpuart
> - amba
> - imx
> - max310x
> - omap-serial
> - sc16is7xx
> - stm32-usart

It looks like there's more of this cruft left at least in
serial8250_em485_config()...

Thanks,

Lukas