Re: calling runtime PM from system PM methods

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

quoted

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