Date: Mon, 07 Oct 2013 14:56:25 -0600 From: Ian Lepore <ian@FreeBSD.org> To: Zbigniew Bodek <zbb@FreeBSD.org> Cc: freebsd-current <freebsd-current@FreeBSD.org>, "freebsd-arm@freebsd.org" <freebsd-arm@FreeBSD.org>, "freebsd-embedded@freebsd.org" <freebsd-embedded@FreeBSD.org> Subject: Re: Changes to UART ns8250 Message-ID: <1381179385.1130.18.camel@revolution.hippie.lan> In-Reply-To: <CALF_TxmfGGeTzgMNVdz-HUn6G=mdgZjiTo8%2BLC8tcrn%2BVvShHg@mail.gmail.com> References: <CALF_Tx=AwVnr0d75-K-yu97iVgmTJC7aaABoix73zHD%2B5eKJnQ@mail.gmail.com> <CAJ-VmokZHvLpUvvD9s8ES0PT%2BE1oVfHWhdbiXF77osBOK2_Yqg@mail.gmail.com> <CALF_TxmfGGeTzgMNVdz-HUn6G=mdgZjiTo8%2BLC8tcrn%2BVvShHg@mail.gmail.com>
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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@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
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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)
@@ -614,6 +614,7 @@ 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);
}
@@ -652,6 +653,16 @@ 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);
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