Subject: Re: 2.6.22 regression: thermal trip points
From: Thomas Renninger <trenn@suse.de>
Reply-To: trenn@suse.de
To: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Adrian =?ISO-8859-1?Q?Schr=F6ter?= <adrian@suse.de>,
       Knut Petersen <Knut_Petersen@t-online.de>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, pavel@ucw.cz, lenb@kernel.org,
       "Zhang, Rui" <rui.zhang@intel.com>, Jean Delvare <khali@linux-fr.org>,
       Alexey Starikovskiy <aystarik@gmail.com>
In-Reply-To: <20070802115631.GA29735@srcf.ucam.org>
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Organization: Novell/SUSE
Date: Thu, 02 Aug 2007 14:42:19 +0200
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On Thu, 2007-08-02 at 12:56 +0100, Matthew Garrett wrote:
> 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.
And often we can provide a boot param or whatever, that makes it at
least useable.
> 
> >   - 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.
*whenever possible*
> 
> >   - 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.
But we cannot (copy all windows (mis-)behavior).
> 
> > > 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)
"I've seen no evidence that this happens...", but I see the point.
> > 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?
For Adrian it would be enough to be able to lower them.
Also being able to define a passive trip point (even if not provided by
BIOS) could help a lot machines.

What about at least:
  - Be able to override passive cooling trip point
  - If BIOS does not provide one, let user be able to define it
This should already make a lot people happy.

    Thomas


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