On Sunday, June 12, 2011, Alan Stern wrote: > 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. I agree. Moreover, calling pm_runtime_resume() from a .prepare() callback is actually fine, because it makes .runtime_resume() run before .suspend() and .suspend_noirq(). But if .runtime_resume() is run between .suspend() and .suspend_noirq(), that may lead to some trouble, again, depending on the subsystem (or PM domain) involved. Also, if a subsystem calls pm_runtime_resume() in one of its system suspend callbacks (e.g. .prepare()), that's pretty much OK, because the subsystem is basically responsible for making things work at this point. However, if a driver does that, it's kind of like saying "here I'm smarter than the subsystem and I know better". Unfortunately, platform drivers deal with a dumb subsystem, so they have the right to think so, but that's not the case in general. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
