Re: [PATCH] time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile timeoptimizaitons

From: John Stultz
Date: Wed Apr 24 2013 - 17:26:25 EST

On 04/24/2013 12:44 PM, Kay Sievers wrote:
On Wed, Apr 24, 2013 at 8:32 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
Kay Sievers noted that the ALWAYS_USE_PERSISTENT_CLOCK config,
which enables some minor compile time optimization to avoid
uncessary code in mostly the suspend/resume path could cause
problems for userland.

In particular, the dependency for RTC_HCTOSYS on
!ALWAYS_USE_PERSISTENT_CLOCK, which avoids setting the time
twice and simplifies suspend/resume, has the side effect
of causing the /sys/class/rtc/rtcN/hctosys flag to always be
zero, and this flag is commonly used by udev to setup the
/dev/rtc symlink to /dev/rtcN, which can cause pain for
older applications.
An alternative to reverting this could be to set that flag
unconditionally on the rtc that matches the persistent clock the
kernel uses internally?

I mean regardless of the pretty weird config option
CONFIG_RTC_HCTOSYS_DEVICE, which internally just does a strcmp() with
the given device name when the flag is queried. :)

Can't we just have the same interface and your original optimization
on x86, even without CONFIG_RTC_HCTOSYS_DEVICE enabled at all?

This might be possible, but I'd rather it be part of the unification work w/ the persistent_clock and the RTC code, rather then a quick hack.


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