On Tue, Oct 20, 2015 at 10:40:03AM -0400, Alan Stern wrote:

Furthermore, that applies only to devices that use synchronous suspend.  
Async suspend is becoming common, and there the only restrictions are 
parent-child relations plus whatever explicit requirements that drivers 
impose by calling device_pm_wait_for_dev().

Hrm, this is the first I'd noticed that feature though I see the initial
commit dates from January.  It looks like most of the users are PCs at
the minute but we should be using it more widely for embedded things,
there's definitely some cases I'm aware of where it will allow us to
remove some open coding.

It does seem like we want to be feeding dependency information we
discover for probing way into the suspend dependencies...