linux-kernel - Re: [RFC][PATCH 0/14] Convert remaining arches to read/update_persistent

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Message-ID: <10f740e80912230208g6237c530k8c70d9375efbd463@mail.gmail.com>
Date:	Wed, 23 Dec 2009 11:08:51 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	john stultz <johnstul@...ibm.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Richard Henderson <rth@...ddle.net>,
	linux-alpha@...r.kernel.org, linux-sh@...r.kernel.org,
	Russell King <linux@....linux.org.uk>,
	Haavard Skinnemoen <hskinnemoen@...el.com>,
	Mike Frysinger <vapier@...too.org>,
	Mikael Starvik <starvik@...s.com>,
	David Howells <dhowells@...hat.com>,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Tony Luck <tony.luck@...el.com>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Kyle McMartin <kyle@...artin.ca>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [RFC][PATCH 0/14] Convert remaining arches to 
	read/update_persistent_clock

On Wed, Dec 23, 2009 at 06:08, Paul Mundt <lethal@...ux-sh.org> wrote:
> On Tue, Dec 22, 2009 at 07:59:22PM -0800, john stultz wrote:
>> In this case the generic read_persistent_clock() and
>> update_persistent_clock() methods have been provided to allow the
>> generic timekeeping code to initialize xtime and set the persistent
>> clock when NTP is synced. However many arches haven't converted, so the
>> generic code has to handle the case where the arch is doing this
>> management itself.
>>
>> This patch series tries to convert the following 14 architectures over
>> to use read_persistent_clock() and update_persistent_clock() as
>> applicable, killing off about 200 lines of arch specific code.
>>
> While I think that this is a good goal, many of the underlying
> architectures have veered pretty far away from having meaningful
> persistent clock interfaces after having moved entirely to generic
> timekeeping and the RTC subsystem.

Indeed. When moving to the RTC subsystem, you loose the persistent
clock at boot;
i.e. on m68k, mach_hwclk() can no longer be set, as the RTC driver is
in a separate
(possible loadable) module.

> In the case of SH at least that interface along with the generic CMOS
> stuff is largely a stop-gap for antiquated platforms that don't have
> proper RTC drivers and likely never will, while the default for all of
> the rest of the platforms effectively returns a fixed dummy value. I
> copied this approach from MIPS originally, so there are at least a few
> architectures that this will apply to.
>
> In any event, I wonder if it might make more sense to take something like
> the SPARC implementation that is simply a wrapper around the RTC, move
> that out in to a more generic place, and permit architectures to select
> an RTC class backed persistent clock instead (it seems to be only
> platforms that haven't caught up yet in terms of generic time and RTC
> migration that would want to define this interface on their own at all at
> this point)?

Hmm, haven't looked into how SPARC handles this yet...
Yes, looks like a good idea to me. Any disadvantages with this approach?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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