On Thu, 24 Dec 2015, Oliver Neukum wrote: > On Wed, 2015-12-23 at 20:32 -0500, Alan Stern wrote: > > > I don't understand why the wakeup conditions are different. It seems > > to me that the choice of which packets will generate a wakeup ought to > > depend on the user's selection, not on the kind of suspend. For > > instance, if the user says that only a magic packet should cause a > > wakeup then that should be true for both runtime suspend and system > > suspend. > > > > To put it another way, as far as the device is concerned a suspend is > > just a suspend -- there's no different between a runtime suspend and a > > system suspend. > > This literally true, but the host and the driver care. > If we autosuspend a running network device, any packet > (maybe filtered for MAC) should cause a remote wake up, > else we'd lose packets. That's also true during system suspend. > But you cannot keep that setting if the system goes down > or any broadcast packet would resume the whole system. > Yet you cannot just disable remote wake up, as WoL packages > still must trigger a remote wake up. This means that sometimes you want to avoid losing packets and other times you do want to lose packets. That is a policy decision, and therefore it should be made by the user, not the kernel. > So there are drivers which must change settings on devices > as the system goes to sleep, even if their devices have > already been autosuspended. We could use the notifier chains > for that. But can this solution be called elegant? Instead of the driver trying to do this automatically, you could rely on userspace telling the driver which packets should cause a wakeup. The setting could be updated immediately before and after each system suspend. I admit this is more awkward than having the driver make a choice based on the type of suspend. This is a case where the resources provided by the PM core aren't adequate for what the driver needs. The PM core distinguishes between wakeup enabled or disabled; it doesn't distinguish among different levels of wakekup. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
