USB: serial: cp210x: add minimun baud rate for CP2105 SCI

USB: serial: cp210x: add minimun baud rate for CP2105 SCI

[Johanna Abrahamsson]

From: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>

This patch adds a minimum baud rate of 2400 for CP2105 SCI

According to the datasheet for CP2105, the SCI supports 2400 as the
lowest baud rate. As this is not heeded in the current code, an error
message 'failed set req 0x1e size 4 status: -32' when trying to set a
lower baud rate such as 300.

Since this is, as far as I can tell, the only cp210x chip with a minimum
baud rate higher than 300, I've added a special case to
cp210x_change_speed rather than adding a min_speed field in
cp210x_serial_private.

Signed-off-by: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>
---
 drivers/usb/serial/cp210x.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index 336a3c0f9f2c..181abf7bb8c0 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -1111,9 +1111,12 @@ static void cp210x_change_speed(struct tty_struct *tty,
 	 */
 	if (priv->use_actual_rate)
 		baud = cp210x_get_actual_rate(serial, baud);
-	else if (baud < 1000000)
+	else if (baud < 1000000) {
+		if (priv->partnum == CP210X_PARTNUM_CP2105 &&
+		    cp210x_interface_num(serial) == 1)
+			baud = clamp(baud, 2400u, priv->max_speed);
 		baud = cp210x_get_an205_rate(baud);
-	else if (baud > priv->max_speed)
+	} else if (baud > priv->max_speed)
 		baud = priv->max_speed;
 
 	dev_dbg(&port->dev, "%s - setting baud rate to %u\n", __func__, baud);

USB: serial: cp210x: add minimun baud rate for CP2105 SCI

[Johan Hovold]

On Mon, Feb 04, 2019 at 12:21:30PM +0100, Johanna Abrahamsson wrote:
> From: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>
> 
> This patch adds a minimum baud rate of 2400 for CP2105 SCI
> 
> According to the datasheet for CP2105, the SCI supports 2400 as the
> lowest baud rate. As this is not heeded in the current code, an error
> message 'failed set req 0x1e size 4 status: -32' when trying to set a
> lower baud rate such as 300.

Good to hear to you found the root cause of that failed baudrate
request.

> Since this is, as far as I can tell, the only cp210x chip with a minimum
> baud rate higher than 300, I've added a special case to
> cp210x_change_speed rather than adding a min_speed field in
> cp210x_serial_private.

But please do add a min_speed field instead of special casing which
tends to make the code harder to read.

> Signed-off-by: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>
> ---
>  drivers/usb/serial/cp210x.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> index 336a3c0f9f2c..181abf7bb8c0 100644
> --- a/drivers/usb/serial/cp210x.c
> +++ b/drivers/usb/serial/cp210x.c
> @@ -1111,9 +1111,12 @@ static void cp210x_change_speed(struct tty_struct *tty,
>  	 */
>  	if (priv->use_actual_rate)
>  		baud = cp210x_get_actual_rate(serial, baud);
> -	else if (baud < 1000000)
> +	else if (baud < 1000000) {
> +		if (priv->partnum == CP210X_PARTNUM_CP2105 &&
> +		    cp210x_interface_num(serial) == 1)
> +			baud = clamp(baud, 2400u, priv->max_speed);
>  		baud = cp210x_get_an205_rate(baud);

We already have a clamp in place in cp210x_get_actual_rate() so just add
a similar construct to cp210x_get_actual_rate() and amend
cp210x_init_max_speed() as needed.

> -	else if (baud > priv->max_speed)
> +	} else if (baud > priv->max_speed)
>  		baud = priv->max_speed;
>  
>  	dev_dbg(&port->dev, "%s - setting baud rate to %u\n", __func__, baud);

Johan

USB: serial: cp210x: add minimun baud rate for CP2105 SCI

[Johan Hovold]

On Mon, Feb 04, 2019 at 04:57:00PM +0100, Johan Hovold wrote:
> On Mon, Feb 04, 2019 at 12:21:30PM +0100, Johanna Abrahamsson wrote:
> > From: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>
> > 
> > This patch adds a minimum baud rate of 2400 for CP2105 SCI
> > 
> > According to the datasheet for CP2105, the SCI supports 2400 as the
> > lowest baud rate. As this is not heeded in the current code, an error
> > message 'failed set req 0x1e size 4 status: -32' when trying to set a
> > lower baud rate such as 300.
> 
> Good to hear to you found the root cause of that failed baudrate
> request.
> 
> > Since this is, as far as I can tell, the only cp210x chip with a minimum
> > baud rate higher than 300, I've added a special case to
> > cp210x_change_speed rather than adding a min_speed field in
> > cp210x_serial_private.
> 
> But please do add a min_speed field instead of special casing which
> tends to make the code harder to read.
> 
> > Signed-off-by: Johanna Abrahamsson <johanna.abrahamsson@afconsult.com>
> > ---
> >  drivers/usb/serial/cp210x.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
> > index 336a3c0f9f2c..181abf7bb8c0 100644
> > --- a/drivers/usb/serial/cp210x.c
> > +++ b/drivers/usb/serial/cp210x.c
> > @@ -1111,9 +1111,12 @@ static void cp210x_change_speed(struct tty_struct *tty,
> >  	 */
> >  	if (priv->use_actual_rate)
> >  		baud = cp210x_get_actual_rate(serial, baud);
> > -	else if (baud < 1000000)
> > +	else if (baud < 1000000) {
> > +		if (priv->partnum == CP210X_PARTNUM_CP2105 &&
> > +		    cp210x_interface_num(serial) == 1)
> > +			baud = clamp(baud, 2400u, priv->max_speed);
> >  		baud = cp210x_get_an205_rate(baud);
> 
> We already have a clamp in place in cp210x_get_actual_rate() so just add
> a similar construct to cp210x_get_actual_rate() and amend
> cp210x_init_max_speed() as needed.

Or better still, move the clamp from cp210x_get_actual_rate() to above
these conditionals and make sure to honour min_speed. Then you can drop
the final else-if here too.

> > -	else if (baud > priv->max_speed)
> > +	} else if (baud > priv->max_speed)
> >  		baud = priv->max_speed;
> >  
> >  	dev_dbg(&port->dev, "%s - setting baud rate to %u\n", __func__, baud);

Johan