Re: i386 HPET code

[Vojtech Pavlik]

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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/