linux-kernel - Re: CONFIG_RTC_HCTOSYS lost on x86 with ALWAYS_USE_PERSISTENT

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Date:	Tue, 23 Apr 2013 20:19:32 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Kay Sievers <kay@...y.org>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: CONFIG_RTC_HCTOSYS lost on x86 with ALWAYS_USE_PERSISTENT_CLOCK
 changes?

On 04/23/2013 08:05 PM, Kay Sievers wrote:
> On Wed, Apr 24, 2013 at 4:43 AM, John Stultz <john.stultz@...aro.org> wrote:
>> On 04/23/2013 06:34 PM, Kay Sievers wrote:
>>> Hey,
>>>
>>> what's the intention of:
>>>     e90c83f757fffdacec8b3c5eee5617dcc038338f ?
>>>     x86: Select HAS_PERSISTENT_CLOCK on x86
>>>
>>> It unconditionally sets:
>>>     HAS_PERSISTENT_CLOCK
>>> but:
>>>     RTC_SYSTOHC
>>> got a depends on !HAS_PERSISTENT_CLOCK
>>>
>>> This makes it impossible to sync the system time from the RTC on x86.
>>> What's going on here?
>>
>> So I suspect just some confusion, but let me know if thats wrong and you're
>> actually seeing an issue.
>>
>> SYSTOHC is what *sets the RTC* to the system time when we're synced with
>> NTP.
>>
>> HCTOSYS is what sets the system time from the RTC.
> Right, and RTC_HCTOSYS is not NTP related. It just reads the time from
> the RTC_HCTOSYS_DEVICE at bootup so we do not boot in 1970 time mode.
> We need that it in all cases, at every bootup on x86. But it's no
> longer there with the above commits. :)
On x86 the persistent_clock() is backed by the 
CMOS/EFI/kvm-wall/xen/vrtc clock (all via x86_platform.get_wallclock) 
should be present and we'll initialize the time in timekeeping_init() there.

Its only systems where there isn't a persistent_clock is where the RTC 
layer and the HCTOSYS is helpful.

Again, if you're having a problem where an x86 system isn't getting its 
time initialized correctly, please let me know the details of the system.

thanks
-john



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