Re: [RFC][PATCH 1/4] RTC: Class device support for persistent clock

From: Maciej W. Rozycki
Date: Sun May 18 2008 - 00:45:27 EST

Hi John,

Sorry about the delay -- I have missed your comment in the flood.

On Wed, 7 May 2008, john stultz wrote:

> > As rtc_read_persistent_clock() is not available at the time
> > timekeeping_init() is called, it will now be disabled if the class device
> > is to be used as a reference. In this case rtc_hctosys(), already
> > present, will be used to set up the system time at the late initcall time.
> > This call has now been rewritten to make use of
> > rtc_read_persistent_clock().
> Hrmm. So how is this going to work with suspend and resume?

Hmm, I have never used suspend/resume, so I cannot really comment. Here
is what I gathered by glancing over the code and some bits of

> Ideally, on resume we want to update the clock before interrupts are
> reenabled so we don't get stale time values post-resume. For systems
> that sleep on reading the persistent clock, I'm open to having them
> fix it up as best they can later (partly why the code can handle
> read_persistent_clock() not returning anything), but unless I'm
> misreading this, it seems you're proposing to make systems that do
> have a safe persistent clock have to have the window where code may
> see the pre-suspend time after resume.

Right now it looks the time is restored in two places,
timekeeping_resume() and rtc_resume(). Of course once the transition to
the new RTC infrastructure has been done, one is going to be redundant.
For the time being I think it is harmless to have them both.

That written, both are called from the relevant driver's ->resume()
method. My set of patches does not change it and as far as I can tell if
it worked before, it will work afterwards. As I understand ->resume()
methods may sleep and are called with interrupts already enabled.

> Am I missing something here?

No idea -- anyone?

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