Messages in this thread | | | Date | Thu, 25 Apr 2013 15:02:31 -0600 | From | Jason Gunthorpe <> | Subject | Re: CONFIG_RTC_HCTOSYS lost on x86 with ALWAYS_USE_PERSISTENT_CLOCK changes? |
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On Thu, Apr 25, 2013 at 01:03:00PM -0700, John Stultz wrote: > On 04/25/2013 11:33 AM, Jason Gunthorpe wrote: > >John mentioned they might be kept for embedded - eg size reduction. > >The issue with that idea is if you do not enable the class RTC > >subsystem then there is no way for a small embedded userspace to set > >the RTC. The /dev/rtc* device obviously goes away, but it also turns > >out that that CONFIG_GENERIC_CMOS_UPDATE only works when combined with > >a heavy weight userspace NTPD that runs the kernel PLL properly. The > >kernel NTP code is enormously conservative and it is actually quite > >hard to get it to write to the RTC. An RTC that cannot be set is > >useless, so these days I feel CONFIG_RTC is pragmatically mandatory - > >and my space constrained embedded systems do set it, for these > >reasons. > > So I mentioned that the size-reduciton focused folks might not like > the generic rtc core over the persistent_clock code, but I'm not > convinced that's a reason to keep the persistent clock code (which
What I mean is you can't actually choose to use persistent_clock over rtc core, that is not a choice. The only choice these days it to omit the user space interface to the RTC (eg rtc core). On some platforms the RTC will still get *read* during boot via persisent_clock, but no platform has a way for userspace to *set* via persisent_clock. update_persisent_clock is not connected to userspace anymore.
An unsettable RTC is useless, IMHO.
> I only noted it, because it has come up prior as a complaint when > switching to the RTC core was proposed.
Sure, but, AFAIK, that was a general concern of /dev/rtc vs /dev/rtc0 - however since then we have lost /dev/rtc completely. That means there is no longer any way to access the persistent_clock functions from userspace.
Jason
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