On Monday, 25 of February 2008, Alan Stern wrote: > On Mon, 25 Feb 2008, Alan Stern wrote: > > > The only possible solution is to have the drivers themselves be > > responsible for preventing calls to device_add() or device_register() > > during a system sleep. (It's also necessary to prevent driver binding, > > but this isn't a major issue.) The most straightforward approach is to > > add a new pair of driver methods: one to disable adding children and > > one to re-enable it. Of course this would represent a significant > > addition to the Power Management driver interface. > > > > (Note that the existing suspend and resume methods cannot be used for > > this purpose. Drivers assume that when the suspend method is called, > > it has already been called for all the child devices. This wouldn't be > > true if one of the purposes of the method was to prevent addition of > > new children.) > > On further thought maybe the existing methods can be used, with care. > Drivers would have to assume the responsibility of synchronizing with > their helper threads and stopping addition of new children (something > they should already be doing), and they would also have to check that > all the existing children are already suspended. They should not make > the assumption that the PM core has already suspended all the children. IMO the device driver should assure that no new children will be registered concurrently with the ->suspend() method (IOW, ->suspend() should wait for all such registrations to complete and should prevent any new ones from being started) and it should make it impossible to register any new children after ->suspend() has run. It's the driver's problem how to achieve that. > The PM core could help detect errors here. If it tries to suspend a > device and sees that the device's parent is already suspended, then the > parent's driver has a bug. Yes, I think we ought to fail the suspend in such cases. Still, that's not sufficient to prevent a child from being registered after we've run dpm_suspend(). For this reason, we could also leave dpm_suspend() with dpm_list_mtx held and not release it until the next dpm_resume() is run. That will potentially cause some trouble to CPU hotplug cotifiers, but we can handle that, for example, by using the in_suspend_context() test. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
