linux-kernel - Re: [PATCH] Unhide the SMBus on the Compaq Deskpro EN

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Message-Id: <200806110916.38694.jbarnes@virtuousgeek.org>
Date:	Wed, 11 Jun 2008 09:16:38 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Krzysztof Helt <krzysztof.h1@...pl>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, lm-sensors@...sensors.org, rh1985@...pl
Subject: Re: [PATCH] Unhide the SMBus on the Compaq Deskpro EN

On Wednesday, June 11, 2008 7:53 am Jean Delvare wrote:
> Hi Jesse, hi Krzysztof,
>
> On Tue, 10 Jun 2008 12:02:19 -0700, Jesse Barnes wrote:
> > On Sunday, June 08, 2008 4:47 am Krzysztof Helt wrote:
> > > From: Krzysztof Helt <krzysztof.h1@...pl>
> > >
> > > This patch unhides the SMBus on Compaq Deskpro EN
> > > SFF P667 with the Intel 815E chipset. Unhiding it reveals
> > > a THMC51 hardware monitoring chip.
> > >
> > > Jean Delvare has checked that this machine has no ACPI
> > > magic touching the SMBus nor the hardware monitoring chip,
> > > so this should be safe.
>
> Let it be noted that ACPI is only one of the possible offenders. SMM is
> another one. The user reported that his fan speed was changing speeds so
> something has to be acting upon temperature changes. This could be the
> fan itself, or this could be SMM code changing the registers of the
> chip.
>
> At this point of the investigation, I am still not 100% sure that the
> patch is safe. I'd say it is only safe if the user's fan is actually
> self-regulated based on the temperature.
>
> One easy way to test would be to verify what happens when the
> temperature exceeds 53 degrees C (the high temperature limit) and 78
> degrees C (the critical temperature limit). Typical SMM code would
> change the high and low limits when the high limit is crossed, this
> should be clearly visible in the output of "sensors".
>
> BTW, Krzysztof, what about adding (read-only) support for the critical
> limits to your thmc50 driver? It would be helpful in a situation like
> this.
>
> Another thing to check is whether the value of register 0x19 (analog
> output) changes automatically when the fan speeds up.
>
> Until these tests are done, I consider this patch possibly unsafe and
> not ready to go to Linus (although probably OK for -next).

Ok, thanks for the heads up Jean, I'll keep this one out of the queue I send 
to Linus until we get confirmation about its safety.

Thanks,
Jesse
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