Re: "double" hpet clocksource && hard freeze [bisected]

[john stultz <johnstul@us.ibm.com>]

On Mon, 2007-08-27 at 17:34 -0300, Luiz Fernando N. Capitulino wrote:
> Em Fri, 24 Aug 2007 11:17:34 -0700
> john stultz <johnstul@us.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?

Looking at the git log, the ia64 clocksource code didn't land until
7/20, so I don't think so.

thanks
-john