Re: [PATCH tty-linus] serial: Reduce spinlocked portion of uart_rs485_config()

[Lukas Wunner <lukas@wunner.de>]

On Fri, Sep 22, 2023 at 06:02:28AM +0200, Lukas Wunner wrote:
> On Thu, Sep 21, 2023 at 06:01:41PM +0300, Ilpo Järvinen wrote:
> > On Thu, 21 Sep 2023, Lukas Wunner wrote:
> > > --- a/drivers/tty/serial/serial_core.c
> > > +++ b/drivers/tty/serial/serial_core.c
> > > @@ -1404,12 +1404,18 @@ static void uart_set_rs485_termination(struct uart_port *port,
> > >  static int uart_rs485_config(struct uart_port *port)
> > >  {
> > >  	struct serial_rs485 *rs485 = &port->rs485;
> > > +	unsigned long flags;
> > >  	int ret;
> > >  
> > > +	if (!(rs485->flags & SER_RS485_ENABLED))
> > > +		return 0;
> > > +
> > >  	uart_sanitize_serial_rs485(port, rs485);
> > 
> > There's a subtle change in behavior here, uart_sanitize_serial_rs485() 
> > memset()s rs485 if RS485 is not enabled but the early return above does 
> > not.
> 
> The two callers of uart_rs485_config() only call it if
> (!(uport->rs485.flags & SER_RS485_ENABLED)).

I meant to say "if (uport->rs485.flags & SER_RS485_ENABLED)"
(i.e. without negation).

Otherwise my point still stands. :)

> Adding that early return ensures that the behavior doesn't change.
> 
> So I don't quite see why you think there's a change in behavior?
> Am I missing something?