On 30/04/2019 15:20:08+0300, Baruch Siach wrote: > Hi Alexandre, > > On Tue, Apr 30 2019, Alexandre Belloni wrote: > > On 30/04/2019 14:36:24+0300, Baruch Siach wrote: > >> Hi Alexandre, > >> > >> On Tue, Apr 30 2019, Alexandre Belloni wrote: > >> > >> > While the range of REFERENCE + TIME is actually 33 bits, the counter > >> > itself (TIME) is a 32-bits seconds counter. > >> > > >> > Signed-off-by: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> > >> > --- > >> > drivers/rtc/rtc-digicolor.c | 1 + > >> > 1 file changed, 1 insertion(+) > >> > > >> > diff --git a/drivers/rtc/rtc-digicolor.c b/drivers/rtc/rtc-digicolor.c > >> > index 5bb14c56bc9a..e6e16aaac254 100644 > >> > --- a/drivers/rtc/rtc-digicolor.c > >> > +++ b/drivers/rtc/rtc-digicolor.c > >> > @@ -206,6 +206,7 @@ static int __init dc_rtc_probe(struct platform_device *pdev) > >> > platform_set_drvdata(pdev, rtc); > >> > > >> > rtc->rtc_dev->ops = &dc_rtc_ops; > >> > + rtc->rtc_dev->range_max = U32_MAX; > >> > >> Where can I find documentation on the meaning and usage of the range_max > >> value? I could not find anything in the kernel source. > > > > It should be set to the maximum UNIX timestamp the RTC can be set to > > while keeping range_min to range_max contiguous. > > > > In the digicolor case, you could go up to 8589934590 (Wed Mar 16 > > 12:56:30 UTC 2242) but the driver only writes DC_RTC_REFERENCE and I'm > > not sure it can also update DC_RTC_TIME safely. > > DC_RTC_TIME resets to zero whenever dc_rtc_write writes CMD_RESET to the > DC_RTC_CONTROL register. DC_RTC_REFERENCE keeps the value that > dc_rtc_write stores there. So the driver will return values larger than > U32_MAX if you happen to cross this point in time between dc_rtc_write > and dc_rtc_read. But you can't store a value larger than U32_MAX in > DC_RTC_REFERENCE. > > Will the core RTC code handle the U32_MAX cross correctly? > Yes, this is ok to return a valid value that is higher than range_max. However, at that time, you will not be able to set any alarms anymore as the core doesn't allow to set alarms after range_max. I would think that this is fine because this will happen in 2106 and we have a way to offset the time (the whole goal of setting the range) using device tree. -- Alexandre Belloni, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
