Re: [PATCH] acpi/pm: If failed at validating ACPI PM timer, inhibit future reads.

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

On Fri, 2011-01-14 at 17:02 +0100, Thomas Gleixner wrote:
> On Fri, 14 Jan 2011, john stultz wrote:
> 
> > On Fri, 2011-01-14 at 07:44 -0800, john stultz wrote:
> > > I'm actually looking at a different fix, as I'm worried by Thomas'
> > > comment about hitting the same issue on real hardware if we catch the
> > > same pmtrm value both times.
> > 
> > Konrad: Mind trying the following?
> > 
> > 
> > The conditional (!hpet && !ref_start && !ref_stop) doesn't really make
> > sense. If the refs are null, but hpet is on, we still want to break out.
> > 
> > So checking if both the ref values are the same should handle if we
> > don't have hardware (both null) or if they are the same value (either by
> > invalid hardware, or by chance), which can cause a divzero issue.
> > 
> > NOT FOR INCLUSION, I haven't had my coffee yet.
> > Signed-off-by: John Stultz <johnstul@us.ibm.com>
> > 
> > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > index 823f79a..fa2cb5e 100644
> > --- a/arch/x86/kernel/tsc.c
> > +++ b/arch/x86/kernel/tsc.c
> > @@ -935,7 +935,7 @@ static void tsc_refine_calibration_work(struct work_struct *work)
> >  	tsc_stop = tsc_read_refs(&ref_stop, hpet);
> >  
> >  	/* hpet or pmtimer available ? */
> > -	if (!hpet && !ref_start && !ref_stop)
> > +	if (ref_start == ref_stop)
> >  		goto out;
> >  
> >  	/* Check, whether the sampling was disturbed by an SMI */
> 
> That makes sense, though we really should kill pmtimer when we detect
> that it's crappy.

Agreed. 

thanks
-john