[linux-pm] calling runtime PM from system PM methods

[Alan Stern]

On Sun, 12 Jun 2011, Rafael J. Wysocki wrote:

> > Basically, I think what Rafael was saying before referred to the 
> > general case, where you don't know anything about the subsystem and 
> > can't afford to make assumptions.  But in the real world you'll be 
> > writing a driver for a particular subsystem and you'll know how that 
> > subsystem works.  If the subsystem permits runtime PM calls to be 
> > nested within the system PM routines, feel free to go ahead and use 
> > them.
> 
> But then we get the problem that user space may echo "on" to the
> device's "control" file in sysfs and the whole clever plan basically goes
> south.

That would indeed be a problem if we used pm_runtime_suspend() in the
system suspend code.  But it doesn't prevent us from calling
pm_runtime_resume() during system suspend.

> Moreover, on some systems devices will belong to PM domains and their
> drivers may potentially be used with different PM domains on different
> platforms.  This means that drivers really should not make any assumptions
> about whether or not they can use runtime PM in their system suspend/resume
> routines.  They can't.

Yes, clearly one mustn't make assumptions about unknown subsystems or
PM domains.

Alan Stern