[PATCH v2 1/2] rtc: add rtc-lpc24xx driver

[Josh Cartwright]

On Fri, May 15, 2015 at 06:31:53PM +0200, Joachim Eastwood wrote:
> On 15 May 2015 at 17:23, Josh Cartwright <joshc at ni.com> wrote:
> > Hello again,
> >
> > On Fri, May 15, 2015 at 03:25:05PM +0200, Joachim Eastwood wrote:
> >> Add driver for the RTC found on NXP LPC24xx/178x/18xx/43xx devices.
> >> The RTC provides calendar and clock functionality together with
> >> periodic tick and alarm interrupt support.
> >>
> >> Signed-off-by: Joachim Eastwood <manabian at gmail.com>
> >> ---
[..]
> >> +static int lpc24xx_rtc_read_time(struct device *dev, struct rtc_time *tm)
> >> +{
> >> +     struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
> >> +     u32 ct0, ct1, ct2;
> >> +
> >> +     ct0 = rtc_readl(rtc, LPC24XX_CTIME0);
> >> +     ct1 = rtc_readl(rtc, LPC24XX_CTIME1);
> >> +     ct2 = rtc_readl(rtc, LPC24XX_CTIME2);
> >> +
> >> +     tm->tm_sec  = CT0_SECS(ct0);
> >> +     tm->tm_min  = CT0_MINS(ct0);
> >> +     tm->tm_hour = CT0_HOURS(ct0);
> >> +     tm->tm_wday = CT0_DOW(ct0);
> >> +     tm->tm_mon  = CT1_MONTH(ct1);
> >> +     tm->tm_mday = CT1_DOM(ct1);
> >> +     tm->tm_year = CT1_YEAR(ct1);
> >> +     tm->tm_yday = CT2_DOY(ct2);
> >> +
> >> +     if (rtc_valid_tm(tm) < 0) {
> >> +             dev_warn(dev, "retrieved date and time is invalid\n");
> >> +             rtc_time64_to_tm(0, tm);
> >> +             lpc24xx_rtc_set_time(dev, tm);
> >> +     }
> >> +
> >> +     return 0;
> >
> > Forcing the read time to be the epoch on failure seems like a pretty
> > poor way to handle errors, in my opinion.
> 
> When the device doesn't have battery the CTIME registers contains an
> invalid value. So if you don't set them to something valid you will
> get a warning each time you try to read the RTC. To "fix" that problem
> I set the time at epoch which make the CTIME registers to contain a
> valid value. Since the value is already useless I think setting it to
> epoch is an improvement in this case.

I see.  I think doing this setting in your read_time callback is the
wrong place to do this check.  I'm thinking a better place for it would
be in your driver's probe().

> I guess it deserves a comment in the driver.

Yes, I agree.

  Josh
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