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    SubjectRe: 2.6.22-rc1-mm1 [cannot change thermal trip points]
    On Thu, 2007-05-17 at 15:17 -0400, Len Brown wrote:
    > On Thursday 17 May 2007 05:23, Pavel Machek wrote:
    > > > ACPI: thermal trip points are read-only
    > >
    > > What was the rationale? Can we get this one reverted?
    > >
    > > Some machines (HP omnibook xe3) have broken trip points -- too high --
    > > so machine will overheat and trigger hw shutdown before starting
    > > passive cooling.
    > >
    > > That's really broken, and write to trip points is reasonable way to
    > > 'fix' that. (I'd understand if you only ever let trip points to
    > > decrease... but otoh root should be able to shoot himself....)
    > No, writing trip-points is neither a fix, nor it is reasonable.
    > It is a workaround at best, and it is a dangerous and mis-leading hack.
    Yes it is a workaround for critical ACPI bugs like that or similar:

    It's also convenient to e.g. lower passive trip point to avoid fan

    Some people are used to it, I already wanted to write a little userspace
    prog to use them as it is really easy to fake cooling_mode (trip points
    are modified by BIOS) and eliminate fan noise and other things by e.g.
    reducing passsive or whatever trip point.

    This is at least a major sysfs interface change, has this been discussed
    somewhere before or declared deprecated?

    It's there for a long time, why is this "a dangerous and mis-leading
    hack." now?

    I'd suggest to revert this and I can come with something like "only
    allow lower values
    than BIOS provides" patch if the current implementation is considered


    > The OS has no capability to actually change the ACPI trip points
    > that are used by the BIOS. Changing the OS copy of them
    > to make the user think that trip events will actually
    > happen when the temperature crosses the OS copy is crazy.
    > If there are systems with broken thermals and the
    > ACPI thermal control needs and over-ride to turn
    > on the fan, then that is fine -- but using
    > fake trip-points and giving the user the impression
    > that they are real is not viable.

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