On Mon, 7 Dec 2009, Linus Torvalds wrote: > > > On Mon, 7 Dec 2009, Alan Stern wrote: > > > > There's no need to suspend the individual devices when the whole system > > is going down. They will automatically suspend when the controller > > stops sending out SOF packets, which occurs when the root hub is > > suspended. The USB spec describes this, grandiosely, as a "global > > suspend". > > Ahh, but the sync vs async would then still matter on resume. No? That's complicated. If we assume the devices weren't runtime-suspended before the sleep began, then they would automatically resume themselves when the controller started transmitting EOF packets. So in that case resume would be fast and async wouldn't matter. But if the devices were runtime-suspended, then what? The safest course is to resume them during the system-wide resume. In that case yes, the sync vs async would matter. And if (as happens on many machines) the firmware messes up the controller settings during resume, then all the USB devices would have to be reset -- another slow procedure. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
