diff mbox series

[v2,4/7] USB: serial: ftdi_sio: Do not reset baud rate to 9600 Baud on error

Message ID 20220712115306.26471-5-kabel@kernel.org
State New
Headers show
Series ftdi_sio driver improvements | expand

Commit Message

Marek Behún July 12, 2022, 11:53 a.m. UTC 
From: Pali Rohár <pali@kernel.org>

If setting new baud rate fails, all other drivers leave the device at
previous baud rate, only ftdi_sio resets to 9600 Baud.

Change this behavior to that of other drivers so that /dev/ttyUSB*
devices behave in the same way.

Signed-off-by: Pali Rohár <pali@kernel.org>
Tested-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
---
Greg pointed out that this make break some people's workflow, that they
may depend on this behavior.

This is of course possible, although IMO improbable: it would be weird
to depend on the fall back to 9600 Baud on error, instead of expecting
that the baud rate didn't change at all (like in other /dev/ttyUSB*
drivers).

Nonetheless if someone complains that they workflow got broken, we will
need to revert this.
---
 drivers/usb/serial/ftdi_sio.c | 38 ++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 12 deletions(-)

Comments

Johan Hovold July 24, 2022, 12:20 p.m. UTC | #1 
On Tue, Jul 12, 2022 at 01:53:03PM +0200, Marek Behún wrote:
> From: Pali Rohár <pali@kernel.org>
> 
> If setting new baud rate fails, all other drivers leave the device at
> previous baud rate, only ftdi_sio resets to 9600 Baud.

> Change this behavior to that of other drivers so that /dev/ttyUSB*
> devices behave in the same way.

These statements are not true. Several USB serial driver set 9600 baud
on errors for historical reasons. Yet others clamp. It's inconsistent at
best.

> Signed-off-by: Pali Rohár <pali@kernel.org>
> Tested-by: Marek Behún <kabel@kernel.org>
> Signed-off-by: Marek Behún <kabel@kernel.org>
> ---
> Greg pointed out that this make break some people's workflow, that they
> may depend on this behavior.
> 
> This is of course possible, although IMO improbable: it would be weird
> to depend on the fall back to 9600 Baud on error, instead of expecting
> that the baud rate didn't change at all (like in other /dev/ttyUSB*
> drivers).
> 
> Nonetheless if someone complains that they workflow got broken, we will
> need to revert this.

>  static u32 get_ftdi_divisor(struct tty_struct *tty,
> -						struct usb_serial_port *port)
> +			    struct usb_serial_port *port, speed_t old_baud)
>  {
>  	struct ftdi_private *priv = usb_get_serial_port_data(port);
>  	struct device *dev = &port->dev;
> @@ -1322,6 +1322,8 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
>  			__func__, priv->custom_divisor, baud);
>  	}
>  
> +	if (!baud)
> +		baud = old_baud;
>  	if (!baud)
>  		baud = 9600;

This looks like it breaks B0 handling. Either way, an unrelated change.

>  	switch (priv->chip_type) {
> @@ -1330,8 +1332,12 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
>  		if (div_value == -1) {
>  			dev_dbg(dev, "%s - Baudrate (%d) requested is not supported\n",
>  				__func__,  baud);
> -			baud = 9600;
> +			baud = old_baud ? old_baud : 9600;
>  			div_value = ftdi_sio_baud_to_divisor(baud);
> +			if (div_value == -1) {
> +				baud = 9600;
> +				div_value = ftdi_sio_baud_to_divisor(baud);
> +			}
>  			div_okay = 0;
>  		}
>  		break;
> @@ -1340,8 +1346,8 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
>  			div_value = ftdi_232am_baud_to_divisor(baud);
>  		} else {
>  			dev_dbg(dev, "%s - Baud rate too high!\n", __func__);
> -			baud = 9600;
> -			div_value = ftdi_232am_baud_to_divisor(9600);
> +			baud = (old_baud >= 183 && old_baud <= 3000000) ? old_baud : 9600;

And please avoid using the ternary operator which tend to just hurt
readability.

Looks like this needs to be refactored in some way.

> @@ -1525,7 +1536,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
>  		if (priv->flags & ASYNC_SPD_MASK)
>  			dev_warn_ratelimited(&port->dev, "use of SPD flags is deprecated\n");
>  
> -		change_speed(tty, port);
> +		change_speed(tty, port, 0);

Zero has a special meaning (B0).

>  	}
>  	mutex_unlock(&priv->cfg_lock);
>  	return 0;
> @@ -2774,9 +2785,12 @@ static void ftdi_set_termios(struct tty_struct *tty,
>  		/* Drop RTS and DTR */
>  		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
>  	} else {
> +		speed_t old_baud =
> +			old_termios ? tty_termios_baud_rate(old_termios) : 0;

Just use 9600 if you don't have an old termios. The termios rate should
be valid in that case.

Johan
Pali Rohár Aug. 18, 2022, 2:12 p.m. UTC | #2 
On Sunday 24 July 2022 14:20:58 Johan Hovold wrote:
> On Tue, Jul 12, 2022 at 01:53:03PM +0200, Marek Behún wrote:
> > From: Pali Rohár <pali@kernel.org>
> > 
> > If setting new baud rate fails, all other drivers leave the device at
> > previous baud rate, only ftdi_sio resets to 9600 Baud.
> 
> > Change this behavior to that of other drivers so that /dev/ttyUSB*
> > devices behave in the same way.
> 
> These statements are not true. Several USB serial driver set 9600 baud
> on errors for historical reasons. Yet others clamp. It's inconsistent at
> best.
> 
> > Signed-off-by: Pali Rohár <pali@kernel.org>
> > Tested-by: Marek Behún <kabel@kernel.org>
> > Signed-off-by: Marek Behún <kabel@kernel.org>
> > ---
> > Greg pointed out that this make break some people's workflow, that they
> > may depend on this behavior.
> > 
> > This is of course possible, although IMO improbable: it would be weird
> > to depend on the fall back to 9600 Baud on error, instead of expecting
> > that the baud rate didn't change at all (like in other /dev/ttyUSB*
> > drivers).
> > 
> > Nonetheless if someone complains that they workflow got broken, we will
> > need to revert this.
> 
> >  static u32 get_ftdi_divisor(struct tty_struct *tty,
> > -						struct usb_serial_port *port)
> > +			    struct usb_serial_port *port, speed_t old_baud)
> >  {
> >  	struct ftdi_private *priv = usb_get_serial_port_data(port);
> >  	struct device *dev = &port->dev;
> > @@ -1322,6 +1322,8 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> >  			__func__, priv->custom_divisor, baud);
> >  	}
> >  
> > +	if (!baud)
> > +		baud = old_baud;
> >  	if (!baud)
> >  		baud = 9600;
> 
> This looks like it breaks B0 handling. Either way, an unrelated change.

Unreleased to this change.

> >  	switch (priv->chip_type) {
> > @@ -1330,8 +1332,12 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> >  		if (div_value == -1) {
> >  			dev_dbg(dev, "%s - Baudrate (%d) requested is not supported\n",
> >  				__func__,  baud);
> > -			baud = 9600;
> > +			baud = old_baud ? old_baud : 9600;
> >  			div_value = ftdi_sio_baud_to_divisor(baud);
> > +			if (div_value == -1) {
> > +				baud = 9600;
> > +				div_value = ftdi_sio_baud_to_divisor(baud);
> > +			}
> >  			div_okay = 0;
> >  		}
> >  		break;
> > @@ -1340,8 +1346,8 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> >  			div_value = ftdi_232am_baud_to_divisor(baud);
> >  		} else {
> >  			dev_dbg(dev, "%s - Baud rate too high!\n", __func__);
> > -			baud = 9600;
> > -			div_value = ftdi_232am_baud_to_divisor(9600);
> > +			baud = (old_baud >= 183 && old_baud <= 3000000) ? old_baud : 9600;
> 
> And please avoid using the ternary operator which tend to just hurt
> readability.
> 
> Looks like this needs to be refactored in some way.
> 
> > @@ -1525,7 +1536,7 @@ static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
> >  		if (priv->flags & ASYNC_SPD_MASK)
> >  			dev_warn_ratelimited(&port->dev, "use of SPD flags is deprecated\n");
> >  
> > -		change_speed(tty, port);
> > +		change_speed(tty, port, 0);
> 
> Zero has a special meaning (B0).
> 
> >  	}
> >  	mutex_unlock(&priv->cfg_lock);
> >  	return 0;
> > @@ -2774,9 +2785,12 @@ static void ftdi_set_termios(struct tty_struct *tty,
> >  		/* Drop RTS and DTR */
> >  		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
> >  	} else {
> > +		speed_t old_baud =
> > +			old_termios ? tty_termios_baud_rate(old_termios) : 0;
> 
> Just use 9600 if you don't have an old termios. The termios rate should
> be valid in that case.

Ok
Johan Hovold Sept. 13, 2022, 2:54 p.m. UTC | #3 
On Thu, Aug 18, 2022 at 04:12:54PM +0200, Pali Rohár wrote:
> On Sunday 24 July 2022 14:20:58 Johan Hovold wrote:

> > > @@ -2774,9 +2785,12 @@ static void ftdi_set_termios(struct tty_struct *tty,
> > >  		/* Drop RTS and DTR */
> > >  		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
> > >  	} else {
> > > +		speed_t old_baud =
> > > +			old_termios ? tty_termios_baud_rate(old_termios) : 0;
> > 
> > Just use 9600 if you don't have an old termios. The termios rate should
> > be valid in that case.
> 
> Ok

Please trim your replies.

Johan
diff mbox series

Patch

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 5b109714612f..cdbba1a9edd9 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1299,7 +1299,7 @@  static int update_mctrl(struct usb_serial_port *port, unsigned int set,
 
 
 static u32 get_ftdi_divisor(struct tty_struct *tty,
-						struct usb_serial_port *port)
+			    struct usb_serial_port *port, speed_t old_baud)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	struct device *dev = &port->dev;
@@ -1322,6 +1322,8 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 			__func__, priv->custom_divisor, baud);
 	}
 
+	if (!baud)
+		baud = old_baud;
 	if (!baud)
 		baud = 9600;
 	switch (priv->chip_type) {
@@ -1330,8 +1332,12 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 		if (div_value == -1) {
 			dev_dbg(dev, "%s - Baudrate (%d) requested is not supported\n",
 				__func__,  baud);
-			baud = 9600;
+			baud = old_baud ? old_baud : 9600;
 			div_value = ftdi_sio_baud_to_divisor(baud);
+			if (div_value == -1) {
+				baud = 9600;
+				div_value = ftdi_sio_baud_to_divisor(baud);
+			}
 			div_okay = 0;
 		}
 		break;
@@ -1340,8 +1346,8 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 			div_value = ftdi_232am_baud_to_divisor(baud);
 		} else {
 			dev_dbg(dev, "%s - Baud rate too high!\n", __func__);
-			baud = 9600;
-			div_value = ftdi_232am_baud_to_divisor(9600);
+			baud = (old_baud >= 183 && old_baud <= 3000000) ? old_baud : 9600;
+			div_value = ftdi_232am_baud_to_divisor(baud);
 			div_okay = 0;
 		}
 		break;
@@ -1363,9 +1369,9 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 			div_value = ftdi_232bm_baud_to_divisor(baud);
 		} else {
 			dev_dbg(dev, "%s - Baud rate too high!\n", __func__);
-			div_value = ftdi_232bm_baud_to_divisor(9600);
+			baud = (old_baud >= 183 && old_baud <= 3000000) ? old_baud : 9600;
+			div_value = ftdi_232bm_baud_to_divisor(baud);
 			div_okay = 0;
-			baud = 9600;
 		}
 		break;
 	case FT2232H: /* FT2232H chip */
@@ -1377,9 +1383,14 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 			div_value = ftdi_232bm_baud_to_divisor(baud);
 		} else {
 			dev_dbg(dev, "%s - Baud rate too high!\n", __func__);
-			div_value = ftdi_232bm_baud_to_divisor(9600);
+			if (old_baud >= 183 && old_baud < 1200) {
+				baud = old_baud;
+				div_value = ftdi_232bm_baud_to_divisor(baud);
+			} else {
+				baud = (old_baud >= 1200 && old_baud <= 12000000) ? old_baud : 9600;
+				div_value = ftdi_2232h_baud_to_divisor(baud);
+			}
 			div_okay = 0;
-			baud = 9600;
 		}
 		break;
 	} /* priv->chip_type */
@@ -1394,7 +1405,7 @@  static u32 get_ftdi_divisor(struct tty_struct *tty,
 	return div_value;
 }
 
-static int change_speed(struct tty_struct *tty, struct usb_serial_port *port)
+static int change_speed(struct tty_struct *tty, struct usb_serial_port *port, speed_t old_baud)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 	u16 value;
@@ -1402,7 +1413,7 @@  static int change_speed(struct tty_struct *tty, struct usb_serial_port *port)
 	u32 index_value;
 	int rv;
 
-	index_value = get_ftdi_divisor(tty, port);
+	index_value = get_ftdi_divisor(tty, port, old_baud);
 	value = (u16)index_value;
 	index = (u16)(index_value >> 16);
 	if (priv->chip_type == FT2232C || priv->chip_type == FT2232H ||
@@ -1525,7 +1536,7 @@  static int set_serial_info(struct tty_struct *tty, struct serial_struct *ss)
 		if (priv->flags & ASYNC_SPD_MASK)
 			dev_warn_ratelimited(&port->dev, "use of SPD flags is deprecated\n");
 
-		change_speed(tty, port);
+		change_speed(tty, port, 0);
 	}
 	mutex_unlock(&priv->cfg_lock);
 	return 0;
@@ -2774,9 +2785,12 @@  static void ftdi_set_termios(struct tty_struct *tty,
 		/* Drop RTS and DTR */
 		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 	} else {
+		speed_t old_baud =
+			old_termios ? tty_termios_baud_rate(old_termios) : 0;
+
 		/* set the baudrate determined before */
 		mutex_lock(&priv->cfg_lock);
-		if (change_speed(tty, port))
+		if (change_speed(tty, port, old_baud))
 			dev_err(ddev, "%s urb failed to set baudrate\n", __func__);
 		mutex_unlock(&priv->cfg_lock);
 		/* Ensure RTS and DTR are raised when baudrate changed from 0 */