On Sunday 24 July 2022 14:28:43 Johan Hovold wrote:
> On Tue, Jul 12, 2022 at 01:53:05PM +0200, Marek Behún wrote:
> > From: Pali Rohár <pali@xxxxxxxxxx>
> >
> > When ASYNC_SPD_CUST is used, update custom_divisor and c_*speed fields
> > so that they correspond to the newly set baud rate value, so that
> > userspace GET ioctls will see the true baud rate that is being used.
>
> No, this is wrong.
>
> In fact, there's a long-standing bug in this driver which started
> reporting back the actual baud rate when using SPD_CUST.
Hello! And this commit is fixing also this bug as a side change.
> The rate should be left unchanged at 38400 in that case.
With this change, rate in c_cflag is unchanged and stays at B38400.
What is updated is the real baudrate in c_ispeed and c_ospeed
extensions.
It is really wrong? I thought that c_cflag should stay unchanged at
B38400 when ASYNC_SPD_CUST is used.
> > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
> > Tested-by: Marek Behún <kabel@xxxxxxxxxx>
> > Signed-off-by: Marek Behún <kabel@xxxxxxxxxx>
> > ---
> > drivers/usb/serial/ftdi_sio.c | 16 ++++++++++++++++
> > 1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
> > index 5db1293bb7a2..39e8c5d06157 100644
> > --- a/drivers/usb/serial/ftdi_sio.c
> > +++ b/drivers/usb/serial/ftdi_sio.c
> > @@ -1303,6 +1303,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> > {
> > struct ftdi_private *priv = usb_get_serial_port_data(port);
> > struct device *dev = &port->dev;
> > + int fix_custom_divisor = 0;
> > int div_value = 0;
> > int div_okay = 1;
> > int baud;
> > @@ -1317,6 +1318,7 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> > if (baud == 38400 &&
> > ((priv->flags & ASYNC_SPD_MASK) == ASYNC_SPD_CUST) &&
> > (priv->custom_divisor)) {
> > + fix_custom_divisor = 1;
> > baud = DIV_ROUND_CLOSEST(priv->baud_base, priv->custom_divisor);
> > dev_dbg(dev, "%s - custom divisor %d sets baud rate to %d\n",
> > __func__, priv->custom_divisor, baud);
> > @@ -1401,7 +1403,19 @@ static u32 get_ftdi_divisor(struct tty_struct *tty,
> > ftdi_chip_name[priv->chip_type]);
> > }
> >
> > + /* Fix deprecated async-compatible custom_divisor hack and update tty baud rate */
> > + if (fix_custom_divisor) {
> > + priv->custom_divisor = DIV_ROUND_CLOSEST(priv->baud_base, baud);
> > + old_baud = baud;
> > + baud = 38400;
> > + }
> > +
> > tty_encode_baud_rate(tty, baud, baud);
> > +
> > + /* For async-compatible custom_divisor store into TCGETS2 c_*speed fields real baud rate */
> > + if (fix_custom_divisor)
> > + tty->termios.c_ispeed = tty->termios.c_ospeed = old_baud;
> > +
> > return div_value;
> > }
> >
> > @@ -2674,6 +2688,8 @@ static void ftdi_set_termios(struct tty_struct *tty,
> > dev_dbg(ddev, "%s: forcing baud rate for this device\n", __func__);
> > tty_encode_baud_rate(tty, priv->force_baud,
> > priv->force_baud);
> > + termios->c_ispeed = termios->c_ospeed =
> > + DIV_ROUND_CLOSEST(priv->baud_base, priv->custom_divisor);
> > }
> >
> > /* Force RTS-CTS if this device requires it. */
>
> Johan
