Re: [PATCH v2 1/9] i2c: prepare runtime PM support for I2C clientdevices

[Graeme Gregory]

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.

Graeme

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