On Wed, 24 Jun 2009, Rafael J. Wysocki wrote: > > The difficulty is that some USB interface drivers require remote wakeup > > to be enabled while their interfaces are suspended. But remote wakeup > > is a global setting; it doesn't take effect until the entire physical > > device is suspended. (To put it another way, USB has no notion of > > suspending interfaces.) This means we must not allow these interfaces > > to be suspended before the whole device is. But the whole device is > > the parent of the interfaces -- if we can't suspend the children before > > suspending the parent then we're stuck. > > Not if we use the power.ignore_children flag on the parent. > > > Clearly this is something the USB stack has to deal with; it shouldn't > > affect the general PM framework. However the only solution I can think > > of involves subverting the framework, which isn't very nice. The idea > > is to ignore runtime_suspend callbacks for these interface drivers; > > allow them to keep on running even though the PM core thinks they are > > suspended. Then suspend and resume them as part of the callbacks for > > the entire device. (For interface drivers that don't require remote > > wakeup there is no problem; it doesn't matter when they get suspended.) > > > > This will work, but it's a hack. Does anybody have a better idea? > > Well, as I said above, you can set power.ignore_children on the device > and then it can be suspended even if the interfaces aren't. Hmm. The hard part still remains: to make sure that the interfaces don't get suspended without the device also getting suspended. I suppose we could attack this by making the device do a runtime_get on each of the interfaces, which would be released in the device's runtime_suspend method. But then conversely, each interface driver would have to do its gets and puts on the _device's_ resume_counter. If they used the interface counters then the values would never go to 0 and so nothing would ever be suspended. You've got to admit, this does sound rather bizarre. :-) But it ought to work... Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
