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

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Date:	Thu, 25 Apr 2013 09:13:32 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Alexander Holler <holler@...oftware.de>
CC:	Kay Sievers <kay@...y.org>, LKML <linux-kernel@...r.kernel.org>,
	Feng Tang <feng.tang@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Subject: Re: CONFIG_RTC_HCTOSYS lost on x86 with ALWAYS_USE_PERSISTENT_CLOCK
 changes?

On 04/25/2013 12:11 AM, Alexander Holler wrote:
> Am 24.04.2013 18:07, schrieb John Stultz:
>
>>> And why is RTC_SYSTOHC now gone on x86?
>>
>> So summarizing the above, because as much as I'm aware, its always been
>> redundant and unnecessary on x86.  Thus being able at build time to mark
>> it as unnecessary was attractive, since it reduced the code paths
>> running at suspend/resume.
>
> Hmm, I thought RTC_SYSTOHC was there to update the used RTC clock with 
> the time from NTP (and liked that). Therefor I don't understand why it 
> is redundant and unnecessary on x86. Of course, most systems do have 
> something in userspace to set the RTC on shutdown, so it isn't really 
> needed.

Prior to SYSTOHC being introduced, we only synced system time to the RTC 
via update_persistent_clock() on systems that had that interface. 
SYSTOHC is relatively new and lets the system sync to RTCs that don't 
have the persistent clock.

thanks
-john

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