linux-kernel - Re: [patch 43/69] i386: HPET, check if the counter works

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Date:	Tue, 5 Jun 2007 09:56:52 -0700 (PDT)
From:	dean gaudet <dean@...tic.org>
To:	Chris Wright <chrisw@...s-sol.org>
cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Andi Kleen <ak@...e.de>, Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Chuck Ebbert <cebbert@...hat.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Thomas Gleixner <tglx@...utronix.de>,
	guilherme@...tralinf.com.br, johnstul@...ibm.com
Subject: Re: [patch 43/69] i386: HPET, check if the counter works

ugh... do not send email before breakfast.  do not send email before 
breakfast.  nevermind :)

-dean

On Tue, 5 Jun 2007, dean gaudet wrote:

> the HPET specification allows for HPETs with *much* lower resolution than 
> 50us.  in fact Fmin is 10Hz iirc.  (sorry to jump in so late, but i'm 
> about a month behind on the list.)
> 
> -dean
> 
> On Mon, 21 May 2007, Chris Wright wrote:
> 
> > -stable review patch.  If anyone has any objections, please let us know.
> > ---------------------
> > 
> > From: Thomas Gleixner <tglx@...utronix.de>
> > 
> > Some systems have a HPET which is not incrementing, which leads to a
> > complete hang. Detect it during HPET setup.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Chris Wright <chrisw@...s-sol.org>
> > ---
> > [chrisw: Why is this not upstream yet?]
> > 
> > ---
> >  arch/i386/kernel/hpet.c |   24 +++++++++++++++++++++++-
> >  1 file changed, 23 insertions(+), 1 deletion(-)
> > 
> > --- linux-2.6.21.1.orig/arch/i386/kernel/hpet.c
> > +++ linux-2.6.21.1/arch/i386/kernel/hpet.c
> > @@ -226,7 +226,8 @@ int __init hpet_enable(void)
> >  {
> >  	unsigned long id;
> >  	uint64_t hpet_freq;
> > -	u64 tmp;
> > +	u64 tmp, start, now;
> > +	cycle_t t1;
> >  
> >  	if (!is_hpet_capable())
> >  		return 0;
> > @@ -273,6 +274,27 @@ int __init hpet_enable(void)
> >  	/* Start the counter */
> >  	hpet_start_counter();
> >  
> > +	/* Verify whether hpet counter works */
> > +	t1 = read_hpet();
> > +	rdtscll(start);
> > +
> > +	/*
> > +	 * We don't know the TSC frequency yet, but waiting for
> > +	 * 200000 TSC cycles is safe:
> > +	 * 4 GHz == 50us
> > +	 * 1 GHz == 200us
> > +	 */
> > +	do {
> > +		rep_nop();
> > +		rdtscll(now);
> > +	} while ((now - start) < 200000UL);
> > +
> > +	if (t1 == read_hpet()) {
> > +		printk(KERN_WARNING
> > +		       "HPET counter not counting. HPET disabled\n");
> > +		goto out_nohpet;
> > +	}
> > +
> >  	/* Initialize and register HPET clocksource
> >  	 *
> >  	 * hpet period is in femto seconds per cycle
> > 
> > -- 
> > -
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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> > 
> -
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