On Wed, May 14, 2014 at 05:26:20PM +0200, Laurent Pinchart wrote:
> On Wednesday 14 May 2014 12:57:45 Mark Brown wrote:

> > Since the core device probe is deferred until everything it depends on
> > is ready it'll get pushed along the device list so that it appears after
> > everything it needs and hence is suspended first.

> That might solve (part of) the master vs. components dependencies (and even in 
> that case I'm pretty sure that there will be cases where the master needs to 
> be suspended first and cases where th slave(s) need to be suspended first), 
> but it doesn't handle inter-slaves dependencies.

> In the V4L subsystem we've implemented an explicit power management API that 
> "slaves" (called subdevices in V4L) must implement, to be called by the 
> master. That's of course more of a workaround than a perfect (or even good) 
> solution.

Right, that's what the function of the master device is in suspend for
this model - it quiesces the compound device as a whole so that any
interdependencies between the devices have been unwound (including
giving callbacks to the slaves where appropriate).  It gives us a place
to hang everything associated with having the devices so closely
interrelated.

Though as Rafael says with async suspend that gets broken.