linux-kernel - Re: [PATCH] time: Revert ALWAYS_USE_PERSISTENT

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Date:	Wed, 24 Apr 2013 14:26:17 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Kay Sievers <kay@...y.org>
CC:	lkml <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>, Feng Tang <feng.tang@...el.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] time: Revert ALWAYS_USE_PERSISTENT_CLOCK compile time
 optimizaitons

On 04/24/2013 12:44 PM, Kay Sievers wrote:
> On Wed, Apr 24, 2013 at 8:32 PM, John Stultz <john.stultz@...aro.org> 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.

thanks
-john

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