On Fri, 29 Apr 2022, Tomasz Mon wrote:
> On Thu, 2022-04-28 at 20:11 +0300, Ilpo Järvinen wrote:
> > uart_throttle() assumes that a driver provides a throttle function in
> > uart_ops. But not all drivers do and there seems to nothing in
> > serial_core that would set it either. Thus, check it before calling.
>
> If the driver does not provide throttle function, it should not
> set UPSTAT_AUTORTS nor UPSTAT_AUTOXOFF in port->status.
>
> > diff --git a/drivers/tty/serial/serial_core.c
> > b/drivers/tty/serial/serial_core.c
> > index 6a8963caf954..18c9d46e0b85 100644
> > --- a/drivers/tty/serial/serial_core.c
> > +++ b/drivers/tty/serial/serial_core.c
> > @@ -697,7 +697,8 @@ static void uart_throttle(struct tty_struct *tty)
> > mask |= UPSTAT_AUTORTS;
> >
> > if (port->status & mask) {
>
> This if condition is always false if driver did not set UPSTAT_AUTORTS
> nor UPSTAT_AUTOXOFF in port->status.
>
> > - port->ops->throttle(port);
> > + if (port->ops->throttle)
> > + port->ops->throttle(port);
> > mask &= ~port->status;
> > }
> >
>
> I think this patch is incorrect. The assumption is not ".throttle is
> always set" but rather ".throttle is set when UPSTAT_AUTORTS or
> UPSTAT_AUTOXOFF is set".
Right, I kind of ended up concluding that's likely the case after sending
the patch when looking into 9aba8d5b0111 (SERIAL: core: add
throttle/unthrottle callbacks for hardware assisted flow control).
--
i.
