linux-kernel - Re: [PATCH 1/3] timekeeping: Add persistent_clock

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Date:	Fri, 14 Dec 2012 09:37:25 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	linux-kernel@...r.kernel.org, alek.du@...el.com
Subject: Re: [PATCH 1/3] timekeeping: Add persistent_clock_exist flag

Hi John,

Thanks for the review.

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().

> 
> Maybe I'm missing something, but it seems this doesn't change the
> resulting logic of the code, does it?  As I thought we already check
> read_persistent_clocks() output (and make sure its null) before
> using the rtc HCTOSYS_DEVICE.

No, it doesn't change the code logic. 

Thanks,
Feng

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