Re: [PATCH 1/2] rtc: m5441x: add MCF5441x on-chip RTC driver

[Geert Uytterhoeven]

Hi Jean-Michel,

On Tue, 2 Jun 2026 at 13:05, Jean-Michel Hautbois
<jeanmichel.hautbois@xxxxxxxxxx> wrote:
> Le 02/06/2026 à 12:04, Geert Uytterhoeven a écrit :
> > On Tue, 2 Jun 2026 at 10:36, Jean-Michel Hautbois
> > <jeanmichel.hautbois@xxxxxxxxxx> wrote:
> >> Add an rtc-class driver for the Freescale MCF5441x on-chip "robust" RTC.
> >> It provides the time/calendar and alarm, and exposes the 2KB
> >> battery-backed standby RAM through the nvmem framework so userspace can
> >> preserve data across a main-power loss (the RAM is retained while
> >> VSTBY_RTC is supplied).
> >>
> >> Register and standby-RAM writes go through the RTC_CR[WE] knock
> >> sequence; the base-2112 year encoding and register map follow the
> >> MCF54418 reference manual. Based on the out-of-tree Freescale 3.0.x
> >> rtc-m5441x driver, rewritten for the current RTC and nvmem APIs.
> >>
> >> Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@xxxxxxxxxx>
> >
> > Thanks for your patch!
> >
> >> +/*
> >> + * The time counters are unstable for an oscillator cycle either side of
> >> + * the one-second boundary. RTC_SR[INVAL] flags this; reads during the
> >> + * window return 0xffff and writes are nullified. Spin until it clears.
> >> + * The window is only a couple of 32kHz cycles (~60us), so bound the
> >> + * busy-wait tightly: it runs with the lock held and interrupts off.
> >> + * Caller holds p->lock.
> >> + */
> >> +static int m5441x_rtc_wait_valid(struct m5441x_rtc *p)
> >> +{
> >> +       unsigned int tries = 10;
> >> +
> >> +       while (rtc_rd(p, M5441X_RTC_SR) & M5441X_RTC_SR_INVAL) {
> >> +               if (!--tries)
> >> +                       return -EIO;
> >> +               udelay(10);
> >> +       }
> >
> > Please use read_poll_timeout().
>
> As wait_valid() is called after spin_lock_irqsave() is called, I suppose
> I should use read_poll_timeout_atomic() ? Because read_poll_timeout()
> sleeps ?

Sorry, I copy and pasted the wrong function name, so you're right.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds