Re: [PATCH] rtc: class: Fix max epoch in rtc_hctosys on 32-bit systems

[Alexandre Belloni <alexandre.belloni@bootlin.com>]

On 18/02/2025 13:45:56+0100, Einar Jón wrote:
> Hello again
> 
> On second thought, removing is too general.
> But it's still very much broken. Is there any reason why this was not
> merged?
> https://lore.kernel.org/all/c5e8ab50-aacb-4651-8893-a6dd9edcd155@app.fastmail.com/T/
> 
> Any thoughts on how this should be handled?

The first step is to convince Lennart that mandating RTC_HCTOSYS xwas a
bad idea, the second step is to let userspace set the time instead. The
kernel can't take the proper decision because it simply doesn't know
whether userspace is TIME64 ready or not.

> 
> Best regards
> Einar Jón
> 
> On Tue, 18 Feb 2025 at 12:12, Einar Jon Gunnarsson <tolvupostur@gmail.com>
> wrote:
> 
> > The check for BITS_PER_LONG == 32 makes no sense after calling
> > tv64.tv_sec = rtc_tm_to_time64(&tm);
> >
> > With this check, any 32-bit system will silently return an -ERANGE error
> > instead of setting the correct time if the hardware clock is storing a
> > date after Y2K38 (2038-01-19).
> > Without this check they should all work as intended, since the rest of
> > the function is perfectly 64-bit safe.
> >
> > Fixes: f9b2a4d6a5f1 ("rtc: class: support hctosys from modular RTC
> > drivers")
> >
> > Signed-off-by: Einar Jon Gunnarsson <tolvupostur@gmail.com>
> > ---
> >  drivers/rtc/class.c | 7 -------
> >  1 file changed, 7 deletions(-)
> >
> > diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
> > index e31fa0ad127e..df58edf99ed3 100644
> > --- a/drivers/rtc/class.c
> > +++ b/drivers/rtc/class.c
> > @@ -72,13 +72,6 @@ static void rtc_hctosys(struct rtc_device *rtc)
> >
> >         tv64.tv_sec = rtc_tm_to_time64(&tm);
> >
> > -#if BITS_PER_LONG == 32
> > -       if (tv64.tv_sec > INT_MAX) {
> > -               err = -ERANGE;
> > -               goto err_read;
> > -       }
> > -#endif
> > -
> >         err = do_settimeofday64(&tv64);
> >
> >         dev_info(rtc->dev.parent, "setting system clock to %ptR UTC
> > (%lld)\n",
> > --
> > 2.34.1
> >
> >
> 
> -- 
> Regards
> Einar Jón

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com