From: Feng Tang <feng.tang@intel.com>
To: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Cc: John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-kernel@vger.kernel.org, alek.du@intel.com
Subject: Re: [PATCH 1/3] timekeeping: Add persistent_clock_exist flag
Date: Thu, 20 Dec 2012 15:02:55 +0800 [thread overview]
Message-ID: <20121220070255.GB16475@feng-snb> (raw)
In-Reply-To: <20121214023826.GA31613@obsidianresearch.com>
Hi Jason,
On Thu, Dec 13, 2012 at 07:38:26PM -0700, Jason Gunthorpe wrote:
>
> > 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?
I read the counter_32k.c and the read_persistent_clock() magic for
ARM, and got a question: for the omap platforms using the
counter_32k.c's read_persistent_clock, why will they also calles
the time service from RTC device like the rtc_suspend/resume? I
thought usually we just need to use the time source with the better
accuracy.
Thanks,
Feng
>
> 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
prev parent reply other threads:[~2012-12-20 7:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-13 2:05 [PATCH 1/3] timekeeping: Add persistent_clock_exist flag Feng Tang
2012-12-13 2:05 ` [PATCH 2/3] rtc: Skip the suspend/resume handling if persistent clock exist Feng Tang
2012-12-13 2:05 ` [PATCH 3/3] rtc: Skip setting xtime if persisent " Feng Tang
2012-12-14 1:20 ` [PATCH 1/3] timekeeping: Add persistent_clock_exist flag John Stultz
2012-12-14 1:37 ` Feng Tang
2012-12-14 2:00 ` John Stultz
2012-12-14 2:15 ` Feng Tang
2012-12-14 2:38 ` Jason Gunthorpe
2012-12-14 3:13 ` Feng Tang
2012-12-14 4:10 ` Jason Gunthorpe
2012-12-14 21:22 ` John Stultz
2012-12-14 21:56 ` Jason Gunthorpe
2012-12-14 23:23 ` John Stultz
2012-12-17 16:14 ` Feng Tang
2012-12-17 18:22 ` Jason Gunthorpe
2012-12-18 2:44 ` Feng Tang
2012-12-14 21:36 ` John Stultz
2012-12-20 7:02 ` Feng Tang [this message]
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