Subject: RE: "double" hpet clocksource && hard freeze [bisected]
From: john stultz <johnstul@us.ibm.com>
To: "Luck, Tony" <tony.luck@intel.com>, Andrew Morton <akpm@osdl.org>
Cc: Paolo Ornati <ornati@fastwebnet.it>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Bob Picco <bob.picco@hp.com>
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Date: Fri, 24 Aug 2007 11:43:23 -0700
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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.

Ok, since no one screamed too badly about this one, and it does fix this
issue, I'm sending it out for reals.

I think Bob's patch which addresses duplicate clocksources should go in,
but this one is a little more forceful in keeping the wrong hpet
clocksource from possibly being selected. 

Andrew, would you mind picking this up?

thanks
-john


The ia64 hpet clocksource was implemented in generic code, and is not
yet ready to replace the i386 and x86_64 implementations. This results
in multiple hpet clocksources being registered, and if the ia64 one is
chosen on x86_64 some users have experienced hangs.

This patch only allows the generic implementation to be used on ia64,
until the duplicate i386 and x86_64 versions can be merged in and
tested.

Signed-off-by: John Stultz <johnstul@us.ibm.com>


diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 77bf4aa..c782d8c 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -78,7 +78,17 @@ static struct clocksource clocksource_hpet = {
         .shift          = 10,
         .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
 };
+
+/* XXX - FIXME: i386, x86_64 and ia64 all have separate 
+ * hpet clocksource implementations. They should be merged 
+ * and this would be a good place for it.
+ * Right now this is ia64 only.
+ */
+#ifdef CONFIG_IA64
 static struct clocksource *hpet_clocksource;
+#else /* this isn't generic enough to use for everyone yet */
+static struct clocksource *hpet_clocksource = (struct clocksource*)0xdead;
+#endif
 
 /* A lock for concurrent access by app and isr hpet activity. */
 static DEFINE_SPINLOCK(hpet_lock);


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