[PATCH V2] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[PATCH V2] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[Matthias Fuchs]

Some Exar UARTs support a auto rs485 mode. In this mode
the UART's RTS# pin is activated during transmitting and
can be used to enable a rs485 line driver. This has nothing
to do with attempts to do this by manually by asserting/
deasserting handshake lines.

Signed-off-by: Matthias Fuchs <mfuchs@ma-fu.de>
---
 drivers/serial/8250.c      |   64 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/serial_reg.h |    1 +
 2 files changed, 65 insertions(+), 0 deletions(-)

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 303272a..4b89f8a 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -2511,6 +2511,69 @@ serial8250_type(struct uart_port *port)
 	return uart_config[type].name;
 }
 
+static int
+serial8250_ioctl_port(struct uart_port *port, unsigned int cmd, unsigned long arg)
+{
+	struct uart_8250_port *up = (struct uart_8250_port *)port;
+	unsigned long flags;
+
+	switch (cmd) {
+	case TIOCSRS485:
+	{
+		struct serial_rs485 rs485ctrl;
+		unsigned char fctr;
+
+		if (port->type != PORT_16850)
+			return -ENOTTY;
+
+		if (copy_from_user(&rs485ctrl,
+				   (struct serial_rs485 *)arg,
+				   sizeof(rs485ctrl)))
+			return -EFAULT;
+
+		spin_lock_irqsave(&up->port.lock, flags);
+		serial_outp(up, UART_LCR, 0xbf);
+		fctr = serial_inp(up, UART_FCTR);
+		if (rs485ctrl.flags & SER_RS485_ENABLED)
+			fctr |= UART_FCTR_RS485;
+		else
+			fctr &= ~UART_FCTR_RS485;
+		serial_outp(up, UART_FCTR, fctr);
+		serial_outp(up, UART_LCR, 0);
+		spin_unlock_irqrestore(&up->port.lock, flags);
+		return 0;
+	}
+
+	case TIOCGRS485:
+	{
+		struct serial_rs485 rs485ctrl;
+
+		if (port->type != PORT_16850)
+			return -ENOTTY;
+
+		spin_lock_irqsave(&up->port.lock, flags);
+		serial_outp(up, UART_LCR, 0xbf);
+		if (serial_inp(up, UART_FCTR) & UART_FCTR_RS485)
+			rs485ctrl.flags = SER_RS485_ENABLED;
+		else
+			rs485ctrl.flags = 0;
+		serial_outp(up, UART_LCR, 0);
+		spin_unlock_irqrestore(&up->port.lock, flags);
+
+		if (copy_to_user((struct serial_rs485 *)arg,
+				 &rs485ctrl,
+				 sizeof(rs485ctrl)))
+			return -EFAULT;
+		return 0;
+	}
+
+	default:
+		return -ENOIOCTLCMD;
+	}
+
+	return 0;
+}
+
 static struct uart_ops serial8250_pops = {
 	.tx_empty	= serial8250_tx_empty,
 	.set_mctrl	= serial8250_set_mctrl,
@@ -2529,6 +2592,7 @@ static struct uart_ops serial8250_pops = {
 	.request_port	= serial8250_request_port,
 	.config_port	= serial8250_config_port,
 	.verify_port	= serial8250_verify_port,
+	.ioctl		= serial8250_ioctl_port,
 #ifdef CONFIG_CONSOLE_POLL
 	.poll_get_char = serial8250_get_poll_char,
 	.poll_put_char = serial8250_put_poll_char,
diff --git a/include/linux/serial_reg.h b/include/linux/serial_reg.h
index 96c0d93..086c3e2 100644
--- a/include/linux/serial_reg.h
+++ b/include/linux/serial_reg.h
@@ -191,6 +191,7 @@
 #define UART_FCTR_RTS_8DELAY	0x03
 #define UART_FCTR_IRDA		0x04  /* IrDa data encode select */
 #define UART_FCTR_TX_INT	0x08  /* Tx interrupt type select */
+#define UART_FCTR_RS485		0x08  /* Auto RS485 mode */
 #define UART_FCTR_TRGA		0x00  /* Tx/Rx 550 trigger table select */
 #define UART_FCTR_TRGB		0x10  /* Tx/Rx 650 trigger table select */
 #define UART_FCTR_TRGC		0x20  /* Tx/Rx 654 trigger table select */
-- 
1.5.6.3

Re: [PATCH V2] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[Laurent Pinchart]

Hi Mathias,

On Friday 02 January 2009 17:26:09 Matthias Fuchs wrote:
> Some Exar UARTs support a auto rs485 mode. In this mode
> the UART's RTS# pin is activated during transmitting and
> can be used to enable a rs485 line driver. This has nothing
> to do with attempts to do this by manually by asserting/
> deasserting handshake lines.

I've tested your patch and it mostly works. See comments inline.

> Signed-off-by: Matthias Fuchs <mfuchs@ma-fu.de>
> ---
>  drivers/serial/8250.c      |   64
> ++++++++++++++++++++++++++++++++++++++++++++ include/linux/serial_reg.h |  
>  1 +
>  2 files changed, 65 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index 303272a..4b89f8a 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -2511,6 +2511,69 @@ serial8250_type(struct uart_port *port)
>  	return uart_config[type].name;
>  }
>
> +static int
> +serial8250_ioctl_port(struct uart_port *port, unsigned int cmd, unsigned
> long arg) +{
> +	struct uart_8250_port *up = (struct uart_8250_port *)port;
> +	unsigned long flags;
> +
> +	switch (cmd) {
> +	case TIOCSRS485:
> +	{
> +		struct serial_rs485 rs485ctrl;
> +		unsigned char fctr;
> +
> +		if (port->type != PORT_16850)
> +			return -ENOTTY;
> +
> +		if (copy_from_user(&rs485ctrl,
> +				   (struct serial_rs485 *)arg,
> +				   sizeof(rs485ctrl)))
> +			return -EFAULT;
> +
> +		spin_lock_irqsave(&up->port.lock, flags);
> +		serial_outp(up, UART_LCR, 0xbf);

You need to save the current LCR and restore it when you're done.

> +		fctr = serial_inp(up, UART_FCTR);
> +		if (rs485ctrl.flags & SER_RS485_ENABLED)
> +			fctr |= UART_FCTR_RS485;
> +		else
> +			fctr &= ~UART_FCTR_RS485;
> +		serial_outp(up, UART_FCTR, fctr);
> +		serial_outp(up, UART_LCR, 0);
> +		spin_unlock_irqrestore(&up->port.lock, flags);
> +		return 0;
> +	}
> +
> +	case TIOCGRS485:
> +	{
> +		struct serial_rs485 rs485ctrl;
> +
> +		if (port->type != PORT_16850)
> +			return -ENOTTY;
> +
> +		spin_lock_irqsave(&up->port.lock, flags);
> +		serial_outp(up, UART_LCR, 0xbf);

Same here.

> +		if (serial_inp(up, UART_FCTR) & UART_FCTR_RS485)
> +			rs485ctrl.flags = SER_RS485_ENABLED;
> +		else
> +			rs485ctrl.flags = 0;
> +		serial_outp(up, UART_LCR, 0);
> +		spin_unlock_irqrestore(&up->port.lock, flags);
> +
> +		if (copy_to_user((struct serial_rs485 *)arg,
> +				 &rs485ctrl,
> +				 sizeof(rs485ctrl)))
> +			return -EFAULT;
> +		return 0;
> +	}
> +
> +	default:
> +		return -ENOIOCTLCMD;
> +	}
> +
> +	return 0;
> +}
> +
>  static struct uart_ops serial8250_pops = {
>  	.tx_empty	= serial8250_tx_empty,
>  	.set_mctrl	= serial8250_set_mctrl,

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussee de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75

Re: [PATCH V2] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[Christopher Gibson]

On Fri, 2009-01-02 at 17:26 +0100, Matthias Fuchs wrote:
> Some Exar UARTs support a auto rs485 mode. In this mode
> the UART's RTS# pin is activated during transmitting and
> can be used to enable a rs485 line driver.
 --->8----

> +
> +	case TIOCGRS485:
> +	{
> +		struct serial_rs485 rs485ctrl;

Should the TIOCGRS485 call set delay_rts_before_send structure element
to 0 to demonstrate that there is no delay ability?  memset(&rs485ctrl,
0, sizeof(struct serial_rs485)); missing?

> +
> +		if (port->type != PORT_16850)
> +			return -ENOTTY;
> +
> +		spin_lock_irqsave(&up->port.lock, flags);
> +		serial_outp(up, UART_LCR, 0xbf);
> +		if (serial_inp(up, UART_FCTR) & UART_FCTR_RS485)
> +			rs485ctrl.flags = SER_RS485_ENABLED;
> +		else
> +			rs485ctrl.flags = 0;
> +		serial_outp(up, UART_LCR, 0);
> +		spin_unlock_irqrestore(&up->port.lock, flags);
> +
> +		if (copy_to_user((struct serial_rs485 *)arg,
> +				 &rs485ctrl,
> +				 sizeof(rs485ctrl)))
> +			return -EFAULT;
> +		return 0;
> +	}

-- 
Christopher Gibson <chris@toftronix.com.au>

Re: [PATCH V2] serial: Add ioctl to enable auto rs485 mode with some Exar UARTs

[Matthias Fuchs]

> On Fri, 2009-01-02 at 17:26 +0100, Matthias Fuchs wrote:
> > Some Exar UARTs support a auto rs485 mode. In this mode
> > the UART's RTS# pin is activated during transmitting and
> > can be used to enable a rs485 line driver.
>  --->8----
> 
> > +
> > +	case TIOCGRS485:
> > +	{
> > +		struct serial_rs485 rs485ctrl;
> 
> Should the TIOCGRS485 call set delay_rts_before_send structure element
> to 0 to demonstrate that there is no delay ability?  memset(&rs485ctrl,
> 0, sizeof(struct serial_rs485)); missing?
Yes, that makes sense. I will add the memset and also add the saving of the LCR 
as Laurent requested.

Matthias