Re: [PATCH] rtc: class: Make the time32 hctosys limit configurable

[Arnd Bergmann]

On Tue, Sep 22, 2026, at 23:37, Alexandre Belloni wrote:
> On 19/09/2026 11:16:29+0200, Arnd Bergmann wrote:
>> On Sat, Sep 19, 2026, at 02:10, Karl Mehltretter wrote:
>>
>> config RTC_HCTOSYS_TIME32_LIMIT
>> 	bool "Reject RTC dates after the 2038 cutoff"
>> 	depends on RTC_HCTOSYS && !64BIT && COMPAT_32BIT_TIME
>> 	default y
>> 
>> to completely disallow it. I think we should wait for Alexandre
>> to comment here, as it's his subsystem in the end and I'm sure
>> he has an opinion on the matter.
>> 
>
> I gave it some thought for the past month as this is an issue that is
> regularly brought up.
>
> The first thing is that this is an issue that disappears as soon as
> RTC_HCTOSYS is not used. RTC_HCTOSYS has plenty of issue and one of
> those is that is doesn't actually work well with NTP. There is a fix for
> this and it would slow down every boot by a second or two.

Sure, simply disallowing RTC_HCTOSYS on any build that contains support
for time32 userspace would also avoid this.

> The main issue is that systemd decided to mandate RTC_HCTOSYS when
> raising up the issue, the answer is that it is unacceptable to have logs
> that are not properly dated until userspace sets the system time. But
> letting userspace set the system time simply solves the issue as it will
> always set a time that it can handle, even if not correct.

Not sure what exactly you are suggesting here. Do you mean we should
try again to address this in systemd in order to no longer need
the RTC_HCTOSYS hack?

      Arnd