Date: Fri, 4 Feb 2005 21:03:59 +0100
From: Vojtech Pavlik <vojtech@suse.cz>
To: Andi Kleen <ak@suse.de>
Cc: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
       john stultz <johnstul@us.ibm.com>, lkml <linux-kernel@vger.kernel.org>,
       keith maanthey <kmannth@us.ibm.com>, Max Asbock <masbock@us.ibm.com>,
       Chris McDermott <lcm@us.ibm.com>
Subject: Re: i386 HPET code
Message-ID: <20050204200359.GA5569@ucw.cz>
References: <88056F38E9E48644A0F562A38C64FB6003EA715C@scsmsx403.amr.corp.intel.com> <20050203213026.GF3181@wotan.suse.de> <20050204200238.GA5510@ucw.cz>
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On Fri, Feb 04, 2005 at 09:02:38PM +0100, Vojtech Pavlik wrote:
> On Thu, Feb 03, 2005 at 10:30:26PM +0100, Andi Kleen wrote:
> > On Thu, Feb 03, 2005 at 06:28:27AM -0800, Pallipadi, Venkatesh wrote:
> > > 
> > > Hi John, Andrew,
> > > 
> > > 
> > > Can you check whether only the following change makes the problem go
> > > away. If yes, then it looks like a hardware issue.
> > > 
> > > >	hpet_writel(hpet_tick, HPET_T0_CMP);
> > > >+	hpet_writel(hpet_tick, HPET_T0_CMP); /* AK: why twice? */
> > 
> > 
> > Ask Vojtech (cced), he wrote the x86-64 HPET code.
> 
> It took me a while to remember, but:
>  
> The first write after writing TN_SETVAL to the config register sets the
> counter value, the second write sets the threshold. 
> 
> When you only do the first write you never set the threshold and
> interrupts won't be generated properly.

That means it's not a bug, but a (documented) feature.

-- 
Vojtech Pavlik
SuSE Labs, SuSE CR
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