On Wed, 30 Jun 2004, Oliver Neukum wrote: > > But it does mean that it's effectively impossible to do a power-off > > resume on such a device. When the power gets restored the device will > > have "morphed" and so the hub driver will call usb_disconnect(). Perhaps > > you believe this is acceptable; I have no opinion one way or the other. > > Better than nothing. But is there a reason the determination of "morphed" > state must be made before resume() ?
Yes. The idea is that if a device "morphs" then it's not really the same device any more. That may even be literally true; a device could be unplugged and another one plugged into the same port. (If this happened during a power-on suspend we would know, because the parent hub would report a connect-change event. During a power-off suspend we wouldn't know.) Whether the change is physical or only logical, we don't want to tell a driver it can "resume" using a different device from the one that was suspended! Consider, for example, that after a firmware download and reset, the collection of configurations and interfaces may be completely different. The driver being resumed would be bound to a no-longer-existing interface. > > USB recognizes three different power states: power-on, suspended, and > > power-off. The question is: Should it be possible to use the power-off > > state as a surrogate for an extremely low-power suspend state (like > > suspend-to-disk)? Unfortunately the current API doesn't allow for such > > distinctions; the suspend() method in usb_driver doesn't include an > > argument to indicate which sort of suspend is about to occur. Oddly > > Probably an error. I see no good reason to drop the argument during > the call chain. Although I'm not aware of the original design decisions, I imagine the API was intended to follow the USB specification, which has only one suspended state. Alan Stern ------------------------------------------------------- This SF.Net email sponsored by Black Hat Briefings & Training. Attend Black Hat Briefings & Training, Las Vegas July 24-29 - digital self defense, top technical experts, no vendor pitches, unmatched networking opportunities. Visit www.blackhat.com _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
