Re: Changes to UART ns8250

On Mon, 2013-10-07 at 14:56 -0600, Ian Lepore wrote:
> On Mon, 2013-10-07 at 22:36 +0200, Zbigniew Bodek wrote:
> > Hello Adrian,
> > 
> > Thank you for your remarks.
> > Please check my answers in-line.
> > 
> > Best regards
> > Zbigniew Bodek
> > 
> > 
> > 2013/10/7 Adrian Chadd <adrian_at_freebsd.org>
> > 
> > > Hi,
> > >
> > > You should add:
> > >
> > > * a loop counter, to break out after a while;
> > >
> > [ZBB] In general as long as UART is busy we cannot proceed but if the
> > timeout occurs we could return an error. Do you agree?
> > 
> > > * a DELAY(1) or something.
> > >
> > [ZBB] DELAY is also a busy wait after all. The reasonable solution might be
> > to use ns8250_delay() to get the transmission time and use it for timeout
> > from the first point. I would DELAY(1) in each loop and decrement value
> > acquired from ns8250_delay(). The loop should break during that time or we
> > return an error. What do you think?
> > 
> 
> Is it possible to not busy-wait at all?  Something like the attached?
> 
> -- Ian
> 
> differences between files attachment (temp.diff)
> Index: sys/dev/uart/uart_dev_ns8250.c
> ===================================================================
> --- sys/dev/uart/uart_dev_ns8250.c	(revision 255916)
> +++ sys/dev/uart/uart_dev_ns8250.c	(working copy)
> _at__at_ -614,6 +614,7 _at__at_ ns8250_bus_ipend(struct uart_softc *sc)
>  
>  	if (ns8250->busy_detect && (iir & IIR_BUSY) == IIR_BUSY) {
>  		(void)uart_getreg(bas, DW_REG_USR);
> +		wakeup(&ns8250->busy_detect);
>  		uart_unlock(sc->sc_hwmtx);
>  		return (0);
>  	}
> _at__at_ -652,6 +653,16 _at__at_ ns8250_bus_param(struct uart_softc *sc, int baudra
>  
>  	bas = &sc->sc_bas;
>  	uart_lock(sc->sc_hwmtx);
> +       /*
> +	* When using DW UART with BUSY detection it is necessary to wait
> +	* until all serial transfers are finished before manipulating the
> +	* line control. LCR will not be affected when UART is busy.
> +	*/
> +	while (ns8250->busy_detect && 
> +	    (uart_getreg(bas, DW_REG_USR) & USR_BUSY) == 0) {
> +		msleep(&ns8250->busy_detect, sc->sc_hwmtx, "dwbusy", 10);
> +	}
> +
>  	error = ns8250_param(bas, baudrate, databits, stopbits, parity);
>  	uart_unlock(sc->sc_hwmtx);
>  	return (error);

Ooops, that should be != 0 in that USR_BUSY test.  Also, I haven't
tested this at all because I don't I have any boards that use DW uarts.

-- Ian