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  • Len Brown's avatar
    ACPI: thermal: expose "thermal.tzp=" to set global polling frequency · 730ff34d
    Len Brown authored
    Thermal Zone Polling frequency (_TZP) is an optional ACPI object
    recommending the rate that the OS should poll the associated thermal zone.
    If _TZP is 0, no polling should be used.
    If _TZP is non-zero, then the platform recommends that
    the OS poll the thermal zone at the specified rate.
    The minimum period is 30 seconds.
    The maximum period is 5 minutes.
    (note _TZP and thermal.tzp units are in deci-seconds,
     so _TZP = 300 corresponds to 30 seconds)
    If _TZP is not present, ACPI 3.0b recommends that the
    thermal zone be polled at an "OS provided default frequency".
    However, common industry practice is:
    1. The BIOS never specifies any _TZP
    2. High volume OS's from this century never poll any thermal zones
    Ie. The OS depends on the platform's ability to
    provoke thermal events when necessary, and
    the "OS provided default frequency" is "never":-)
    There is a proposal that ACPI 4.0 be updated to reflect
    common industry practice -- ie. no _TZP, no polling.
    The Linux kernel already follows this practice --
    thermal zones are not polled unless _TZP is present and non-zero.
    But thermal zone polling is useful as a workaround for systems
    which have ACPI thermal control, but have an issue preventing
    thermal events.  Indeed, some Linux distributions still
    set a non-zero thermal polling frequency for this reason.
    But rather than ask the user to write a polling frequency
    into all the /proc/acpi/thermal_zone/*/polling_frequency
    files, here we simply document and expose the already
    existing module parameter to do the same at system level,
    to simplify debugging those broken platforms.
    Note that thermal.tzp is a module-load time parameter only.
    Signed-off-by: default avatarLen Brown <>