Message-ID: <20070827173458.5a1ffed1@localhost>
Date:	Mon, 27 Aug 2007 17:34:58 -0300
From:	"Luiz Fernando N. Capitulino" <lcapitulino@...driva.com.br>
To:	john stultz <johnstul@...ibm.com>
Cc:	Bob Picco <bob.picco@...com>, "Luck, Tony" <tony.luck@...el.com>,
	Paolo Ornati <ornati@...twebnet.it>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: "double" hpet clocksource && hard freeze [bisected]

Em Fri, 24 Aug 2007 11:17:34 -0700
john stultz <johnstul@...ibm.com> escreveu:

| On Fri, 2007-08-24 at 08:46 -0400, Bob Picco wrote:
| > john stultz wrote:	[Thu Aug 23 2007, 05:41:45PM EDT]
| > > On Thu, 2007-08-23 at 14:05 -0700, john stultz wrote:
| > > > On Thu, 2007-08-23 at 13:41 -0700, Luck, Tony wrote:
| > > > > > I have a double "hpet" entry in "available_clocksource":
| > > > > >	$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
| > > > > >	tsc hpet hpet acpi_pm jiffies
| > > > > 
| > > > > Oops.  If seems that both drivers/char/hpet.c and arch/x86_64/kernel/hpet.c
| > > > > both register a clocksource named "hpet".  Probably a result of bringing
| > > > > back to life a long lost patch, and having someone else (John Stultz, according
| > > > > to git blame) make a similar change to a different file in the intervening
| > > > > time.
| > > > > 
| > > > > Presumably the thing to do would be merge the x86_64 specific version
| > > > > into the drivers/char/hpet.c version?
| > > > 
| > > > Ugh. Yea. i386 has an hpet clocksource as well. We should kill the
| > > > duplication, but at the moment I'm not comfortable that the
| > > > driver/char/hpet.c is ok to be used for i386/x86_64 (Bob: Do you know
| > > > why the shift value is only 10?).
| > > > 
| > > > 
| > > > I'm a little surprised by this, as the clocksource code use to prevent
| > > > duplicate named clocksources from being registered, so I'm not sure how
| > > > that check got dropped.  Also I'm not quite sure I see where the hard
| > > > freeze is coming from.
| > > > 
| > > > My initial reaction would be to either ifdef ia64 implementation in
| > > > drivers/char/hpet.c or move the code under the ia64 arch dir until it is
| > > > really usable by all arches.
| > > 
| > > Here is a possible quick fix. I'm open to other approaches, but I also
| > > want to avoid too much churn before 2.6.23 goes out.
| > > 
| > > Paolo, could you verify this fixes the issue for you?
| > > 
| > > thanks
| > > -john
| > > 
| > [snip]
| > 
| > I saw what was missed by me in my brief examination of this last night.
| > The platform registers the hpet clocksource too.
| > 
| > Instead of adding the config flag to hpet driver, how about the patch
| > below? Since you already check for duplication by address then adding
| > a check for by name too seems okay to me.
| > 
| > bob
| > 
| > 
| > Prevent duplicate names being registered with clocksource. This also
| > eliminates the duplication of hpet clock registration when the arch
| > uses the hpet timer and the hpet driver does too. The patch was
| > compile and link tested.
| 
| Yea. While I'm still not completely comfortable leaving this up to boot
| order alone (the ia64 hpet clocksource is clearly causing issues on
| x86_64), I think this patch is something we need as well.

 Does -stable need this too?

-- 
Luiz Fernando N. Capitulino
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