On Thu, Dec 13, 2012 at 06:00:23PM -0800, John Stultz wrote: > 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.
I only studied update_persistent_clock, read_persistent_clock is very much different. Looking at it, I don't think that update_persistent_clock is in any way related to read_persistent_clock.. update_persistent_clock is *only* called by NTP, and its *only* purpose is to update the RTC with NTP synchronized time. In many configurations it will never even be called. I think update_persistent_clock is badly named, it should be called platform_save_ntp_time_to_rtc(), keep it divorced from read_presistent_clock :) > 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. On ARM the read_presistent_clock is used to access a true monotonic counter that is divorced from the system RTC - look at arch/arm/plat-omap/counter_32k.c for instance. This seems like a great use of that hardware resource, and no doubt those mach's also have a class RTC driver available talking to different hardware. For mach's without that functionality ARM returns a fixed 0 value from read_persistent_clock, persumably the kernel detects this and falls back to using class rtc functions? Maybe Feng would be better off adjusting read_persistent_clock to return ENODEV in such cases?? So, I think you have to keep your test as a run time test. To support the single image ARM boot you can't make the distinction with kconfig. Regards, Jason -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/