On Mon, Sep 16, 2013 at 05:38:12PM +0300, Mika Westerberg wrote: > On Mon, Sep 16, 2013 at 11:12:49AM +0100, Mark Brown wrote: > > That's definitely an ACPI specific (probably x86 specific ACPI?) > > requirement not a generic one, on some systems it would increase power > > consumption since the controller will need to sit on while the device is > > functioning autonomously. > > Yes, the ACPI 5.0 spec says that the device cannot be in higher D-state > than its parent. This is not x86 specific, though I'm not sure if this is > implemented elsewhere. > I do not think this stops the OS fine controlling the power of the device though. It is only a mechanism to make sure the tree of D states is vaguely sane from the ACPI point of view. What happens in each D state is never actually defined in the ACPI spec.
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