Re: [RFD] Automatic suspend

Rafael J. Wysocki
2009-02-16T22:12:48Z

On Monday 16 February 2009, Arjan van de Ven wrote:
> On Mon, 16 Feb 2009 22:48:32 +0100
> "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
>
> > > Userland should never ever control the state of a device like this
> > > directly. It should do so by a) closing the device and b) setting
> > > latency / functional requirements.
> >
> > The user, however, may want to forcibly put a device into a low power
> > state without stopping all of the applications that depend on it (eg.
> > have it open). Do you think that we shouldn't allow users to do such
> > things?
>
> I would think that that is a bad mistake to do. It basically breaks the
> contract that the kernel has with userspace....

OK, so I think there are two things that user space may be allowed to do as
far as putting devices into low power states is concerned:
* disable/enable the automatic power management of the device (provided that
the driver supports the automatic PM)
* check what power states devices are in.

Thanks,
Rafael