linux-kernel - Re: 2.6.22 regression: thermal trip points

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Message-ID: <20070802115631.GA29735@srcf.ucam.org>
Date:	Thu, 2 Aug 2007 12:56:31 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Thomas Renninger <trenn@...e.de>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Adrian Schröter <adrian@...e.de>,
	Knut Petersen <Knut_Petersen@...nline.de>,
	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	pavel@....cz, lenb@...nel.org, "Zhang, Rui" <rui.zhang@...el.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Alexey Starikovskiy <aystarik@...il.com>
Subject: Re: 2.6.22 regression: thermal trip points

On Thu, Aug 02, 2007 at 01:45:00PM +0200, Thomas Renninger wrote:
> On Thu, 2007-08-02 at 12:13 +0100, Matthew Garrett wrote:
> > I strongly suspect that the vast majority[1] of hardware that "needs" 
> > the trip points changing works perfectly well under Windows, so it's 
> > likely to be papering over bugs in the kernel. It'd be nice if we fixed 
> > those rather than encouraging people to poke stuff into /proc,
> Some arguments against that:
>   - You cannot tell a customer: Wait for the kernel in half a year.
>     This is the time it at least needs until a laptop got sold, the
>     problem is found, a patch is written and checked in and finally
>     hits the distribution.

We have to do so frequently. New hardware often exposes bugs in the 
kernel.

>   - You can also not backport fixes as ACPI patches mostly have the
>     potential to break other machines/BIOSes
>   - There also exist the policy to not fix up/workaround totally broken
>     AML BIOS implementations

The policy has been to attempt to be bug-compatible with Windows 
whenever possible for some time now.

>   - We do not need to and never will be able to copy or do the same
>     Windows is doing

Given that many vendors still only test against Windows, that's exactly 
what we need to do.

> > especially when doing so is guaranteed to break in really confusing ways 
> > with a lot of hardware. The firmware can reset the trip points at 
> > essentially arbitrary times and is well within its rights to expect the 
> > OS to actually pay attention to them.
> What the hell is so wrong with:
> 
> Let the user override the trip points. If he does so, ignore
> thermal trip point updates from BIOS. Don't care for hysteresis
> BIOS implementations (these are the BIOS trip point updates).

No, that's not the only reason for notifications. Alteration in hardware 
state may also force a recalculation of trip point (adding a battery to 
a bay rather than a DVD drive may require the platform to be kept at a 
lower temperature)

> If user changes them, it's his fault, he doesn't need to...
> Make sure that trip points can only be lowered, compared to the
> initially fetched one from BIOS.

Surely people want this functionality so that they can raise trip 
points?

-- 
Matthew Garrett | mjg59@...f.ucam.org
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