Messages in this thread | | | Date | Fri, 14 Dec 2012 10:15:25 +0800 | From | Feng Tang <> | Subject | Re: [PATCH 1/3] timekeeping: Add persistent_clock_exist flag |
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On Thu, Dec 13, 2012 at 06:00:23PM -0800, John Stultz wrote: > On 12/13/2012 05:37 PM, Feng Tang wrote: > >On Thu, Dec 13, 2012 at 05:20:36PM -0800, John Stultz wrote: > >>On 12/12/2012 06:05 PM, Feng Tang wrote: > >>>In current kernel, there are several places which need to check > >>>whether there is a persistent clock for the platform. Current check > >>>is done by calling the read_persistent_clock() and validating the > >>>return value. > >>> > >>>Add such a flag to make code more readable and call read_persistent_clock() > >>>only once for all the checks. > >>Sorry.. What the actual benefit of this patch set? (Usually with > >>changelogs its better to explain why you're doing something, rather > >>then just what you're doing.) > >The main benefits is not bother to do the rtc_resume and rtc_suspend work > >if persistent clock exists. Current RTC suspend/resume code will do many > >time calculation and compensation work at first, and then call > >timekeeping_inject_sleeptime() which will just return for platform with > >persistent clock, what I did in this patchset is to put the check at > >the start, also I save the persistent_clock_exist flag for all possible > >check after timekeeping_init(). > > CC'ing Jason as his recent patch is conceptually connected here. > > Ok, Feng, so your patch set is a suspend/resume optimization for the > case where the architecture has a read_persistent_clock() > implementation, but the kernel config has also the rtc > HCTOSYS_DEVICE set, right?
Exactly! Sorry for I didn't make it clear
> > So we basically short-cut the rtc's HCTOSYS_DEVICE suspend/resume > logic, likely to speed up suspend/resume. > > So per Jason's related patch, he's made the point that the > persistent_clock and RTC class functionality are basically exclusive > (well, in his case, he said this with respect to updating the RTC, > not reading it - I don't mean to put words in his mouth - Please do > correct me here Jason. :). In other words, we probably should avoid > configurations where both the rtc hctosys and persistent_clock > interfaces are both active.
Yes, I agree these 2 should be exclusive.
> > So my thought here is that this same behavioral change could be made > via Kconfig constraints rather then extra run-time conditionals. > Basically we add a HAS_PERSISTENT_CLOCK, that architectures select > if they want to use the read/update_persistent_clock calls. Then we > make the HCTOSYS option be dependent on !HAS_PERSISTENT_CLOCK. This > way we avoid having configs where there are conflicting paths that > we chose from.
Sounds good to me, and we may need to add the HAS_PERSISTENT_CLOCK to the default config of platforms who implemente the read_persistent_clock().
One concern is if a platform has read_persistent_clock capability, will it also has the write_persistent_clock? The answer may be no
Thanks, Feng
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