* Johan Hovold <johan@xxxxxxxxxx> [220411 09:54]:
> On Mon, Apr 11, 2022 at 12:48:04PM +0300, Tony Lindgren wrote:
> > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> > --- a/drivers/tty/serial/8250/8250_port.c
> > +++ b/drivers/tty/serial/8250/8250_port.c
> > @@ -1681,8 +1681,10 @@ static void serial8250_start_tx(struct uart_port *port)
> > return;
> >
> > if (em485 &&
> > - em485->active_timer == &em485->start_tx_timer)
> > + em485->active_timer == &em485->start_tx_timer) {
> > + serial8250_rpm_put_tx(up);
> > return;
> > + }
>
> I was just taking a quick look at your report about this and also
> noticed this return statement.
>
> The runtime PM implementation is a bit of mess as we've discussed
> elsewhere, but the change you propose here doesn't look right.
Frankly "a bit of mess" applies "a bit more" than just the serial runtime
PM :)
> start_tx() can be deferred in the rs485 case, but that doesn't mean you
> should suspend the device here. In fact, that look like it would just
> break runtime PM (the parts that may work to some extent).
AFAIK there's currently nothing paired with the serial8250_rpm_get_tx(up)
call at the beginning of serial8250_start_tx() for the early exit cases
if start_tx_rs485() or __start_tx() won't get called.
Care to clarify a bit more what you have in mind?
Regards,
Tony
