On Friday 23 March 2007 5:47 pm, Dmitry Krivoschekov wrote: > David Brownell wrote: > >> For example, in USB you are able to enable/disable autosuspend rule, > >> don't know if it's possible to disable it at runtime though. > > > > There are patches to allow disabling it at runtime through sysfs > > attributes of any given device. > > > > The primary reason to have one is bugs in those external devices, > > where they don't behave according to the USB spec. That's the > > If I didn't miss something, the primary reason was to allow > devices to charge batteries from the bus, so, does USB > specs restrict this somehow? Or, what's wrong with that? You're mixing up two distinct issues: - Minimizing power use by the USB host ... to stretch its battery life, or otherwise shrink its power usage, starting with current delivered between on USB (between VBUS and GND). - How the peripheral uses whatever VBUS current it draws ... which can power arbitrary electronics, including a battery charger, but might be nothing more than powering the USB link. (FWIW that's all the Nokia 800 does with VBUS; that helps stretch battery life.) Clearly there's some competition there. The default policy allows autosuspend. The primary reason to disable autosuspend is, as I said, that some devices don't work well with it. (Flakey circuits or firmware, etc.) However, enabling autosuspend *does* have a side effect that would matter for those few devices that use VBUS to recharge a battery: the VBUS current going to a suspended device is almost certainly not enough to recharge anything substantial. So -- for those few devices that do recharge batteries over USB -- yes, another reason to disable autosuspend might be to help recharge a battery. - Dave _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
