linux-kernel - Re: ACPI PM-Timer on K6-3 SiS5591: Houston...

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Message-ID: <20080810094038.141480b4@infradead.org>
Date:	Sun, 10 Aug 2008 09:40:38 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Dominik Brodowski <linux@...inikbrodowski.net>
Cc:	Andreas Mohr <andi@...as.de>, LKML <linux-kernel@...r.kernel.org>,
	john stultz <johnstul@...ibm.com>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-acpi@...r.kernel.org
Subject: Re: ACPI PM-Timer on K6-3 SiS5591: Houston...

On Sun, 10 Aug 2008 18:29:20 +0200
Dominik Brodowski <linux@...inikbrodowski.net> wrote:

> Hi Andreas,
> 
> On Sun, Aug 10, 2008 at 12:17:30PM +0200, Andreas Mohr wrote:
> > Result: catastrophic timer behaviour (a large backwards skip is
> > possible), even in case we do a triple-read workaround, due to a
> > floating bit at 0x0400 (possibly caused by underclocking from 400
> > to 150, but whatever...).
> 
> this isn't the bug which is handled by the
> read-three-times-workaround. Instead, that handels the following
> PIIX4 errata:
> 
>  * PIIX4 Errata:
>  *
>  * The power management timer may return improper results when read.
>  * Although the timer value settles properly after incrementing,
>  * while incrementing there is a 3 ns window every 69.8 ns where the
>  * timer value is indeterminate (a 4.2% chance that the data will be
>  * incorrect when read). As a result, the ACPI free running count up
>  * timer specification is violated due to erroneous reads.
> 
> > And my system does pass the bootup PM-Timer check quite often
> > despite this severe defect (2 in 4 bootups _did_ register my
> > defective acpi_pm clocksource).
> 
> No surprise there -- it is the first time I see such an error; and it
> might actually be a bug specific to your computer's motherboard. 
> 

if it's really only one board that's faulty... a dmi blacklist might be
appropriate.


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