Re: [RFC v2 2/5] PM, Add sysfs file power_off to control devicepower off policy

From: Alan Stern
Date: Thu May 10 2012 - 10:48:12 EST

On Thu, 10 May 2012, Huang Ying wrote:

> How to remove power is not general enough, but I think whether to power
> off is more general. So a flag like power_must_be_on can be general and
> useful.

I'm not so sure about that.

> > Also, from a driver's perspective the result of putting a device into
> > some non-power-off low-power state may be just as unpleasant as the
> > result of removing power from it.
> Yes. From device driver or bus point of view, "power off" is just like
> other low power state. But from the "all devices" point of view, power
> off can be the only low power state that is shared by all devices. So
> we can say "power off" is special from this point of view.

No -- it's not true that all devices share a "power off" state while
the system is running.

The only thing that can be said about all devices is that some of them
can be put into one or many low-power states. That's what the PM core
means when it talks about runtime suspend.

Alan Stern

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at