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

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Date:	Wed, 24 Apr 2013 21:44:47 +0200
From:	Kay Sievers <kay@...y.org>
To:	John Stultz <john.stultz@...aro.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 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?

Kay
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