Re: [RFC] PCI: Runtime power management

On Sat, 15 Aug 2009, Rafael J. Wysocki wrote:

quoted

quoted

Why don't we add a flag indicating whether or not the device is allowed to
be power managed at run time, something like runtime_forbidden, that the
user space will be able to set through sysfs?

I think even having a runtime_wakeup flag (which defaults to on) would 
be sufficient.

Perhaps it would, but then unsetting runtime_wakeup would effectively disable
runtime PM for devices that need it to be power managed at run time (probably
all input devices).  Also there may be situations in which user space may
really want to disable runtime PM for some devices (think of broken hardware
for one example).

It sounds like there are really three choices here, and the decision 
should largely be left up to the user:

	1. don't use runtime PM,

	2. allow runtime PM but disable remote wakeup,

	3. allow runtime PM with remote wakeup enabled.

Now, a driver may say "I can't do my job without remote wakeup".  Such
a driver would refuse to do runtime_suspend in case 2.  But otherwise
we should follow the preference of the user.

The only remaining question is how to expose this in sysfs in a way 
that won't be confusing and that won't be confused with the "wakeup" 
attribute.  One possibility is to use the "level" attribute introduced 
in USB; possible levels are "on" (no runtime PM) and "auto" (runtime 
PM allowed).  Then a new "runtime_wakeup" attribute could contain 
nothing (if wakeup is not available), "enabled", or "disabled".

Alan Stern