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

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Tuesday 21 April 2009, Greg KH wrote:
> 
> I seem to not have seen the original post about this, thanks Alan for
> adding me to the cc:
> 
> On Mon, Apr 20, 2009 at 06:11:18PM -0400, Alan Stern wrote:
> > On Mon, 20 Apr 2009, 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.
> 
> I'm confused, why would a driver not know if it was in use or not?
> Actually, how would it not know already by virtue of what is happening
> within it (io in flight, buttons being pushed, dma streaming, etc.)?
> 
> > > 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?
> 
> So userspace knows better than the kernel as to if a specific driver is
> being used at the moment?  Why is this so?

The name of the flag is not the best one. :-)

The flag is supposed to mean "don't suspend this device during system-wide
suspend, because it's being used for something you may be unaware of".
AFAICS.

Best,
Rafael