linux-kernel - Re: AMD X2 unsynced TSC fix?

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Message-ID: <20061028195739.GA18879@suse.cz>
Date:	Sat, 28 Oct 2006 21:57:39 +0200
From:	Vojtech Pavlik <vojtech@...e.cz>
To:	Lee Revell <rlrevell@...-job.com>
Cc:	Andi Kleen <ak@...e.de>, thockin@...kin.org,
	Jiri Bohac <jbohac@...e.cz>,
	Luca Tettamanti <kronos.it@...il.com>,
	linux-kernel@...r.kernel.org, john stultz <johnstul@...ibm.com>
Subject: Re: AMD X2 unsynced TSC fix?

On Sat, Oct 28, 2006 at 02:22:11PM -0400, Lee Revell wrote:

> On Fri, 2006-10-27 at 20:59 -0700, Andi Kleen wrote:
> > > Fortunately, we usually have an HPET, these days.  You can
> > definitely
> > > resync and get near-linear values of RDTSC.
> > 
> > No we don't -- most BIOS still don't give us the HPET table 
> > even when it is there in hardware. In the future this will change sure
> > but people will still run a lot of older motherboards. 
> 
> I have exactly such a system (see thread "x86-64 with nvidia MCP51
> chipset: kernel does not find HPET").  Is there anything at all I can do
> to make the kernel see the HPET?  Can I try to guess the address?  BIOS
> upgrade?
 
In most cases where the HPET is present but not reported, it's not
configured. Usually, you need to write a chipset-specific register to
configure the address.

Finding the register, finding some free MMIO space, writing the address
to the register and telling the address to the kernel is enough.

-- 
Vojtech Pavlik
Director SuSE Labs
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