Re: [RFC Add in_use attribute] Let the driver know if it's in use

[Greg KH <greg@kroah.com>]

On Tue, Apr 21, 2009 at 07:08:44AM +0200, Michael Trimarchi wrote:
> Hi,
> 
> Greg KH wrote:
> > On Mon, Apr 20, 2009 at 11:54:04PM +0200, Rafael J. Wysocki wrote:
> >   
> >> On Thursday 16 April 2009, Michael Trimarchi wrote:
> >>     
> >>> Drivers on embedded systems would be smart enough
> >>> to know that some of the devices should remain powered up, because
> >>> they could still be useful even when the CPU wasn't running.
> >>> The patch add the in_use attribute, that it can be used by the
> >>> the drivers to avoid power down during suspend.
> >>>       
> >> OK, so the idea is that in_use will be set by the user space for devices that
> >> shouldn't be suspended.  Is this correct?
> >>     
> >
> > If so, why?  Why would you suspend anything then?  Why not just have
> > userspace suspend the devices it wants to suspend and leave the ones it
> > thinks is "in_use" alone?
> >
> >   
> Because it the previus thread the idea is that the driver should use 
> this flag
> 
> "[linux-pm] [RFC Disable suspend on a
> specific device] This is a little change in linux power scheme".

I wasn't involved in that thread, and am not on linux-pm, care to
summarize why this change is now recommended?

> > Exactly, what are you trying to do that differs from
> > device_for_each_child()?
> >   
> Is device for each child use to visist the first level of the tree?

Have you tried it?

thanks,

greg k-h