On Fri, Jul 07, 2023 at 05:12:25PM -0700, Jakub Kicinski wrote: > On Thu, 6 Jul 2023 18:28:58 +0000 Alexandru Gagniuc wrote: > > For Wake-on-LAN to work from S5 (shutdown), the USB link must be put > > in U3 state. If it is not, and the host "disappears", the chip will > > no longer respond to WoL triggers. > > > > To resolve this, add a notifier block and register it as a reboot > > notifier. When WoL is enabled, work through the usb_device struct to > > get to the suspend function. Calling this function puts the link in > > the correct state for WoL to function. > > Would be good to hear from USB experts on this one, to an outside seems > like something that the bus should be doing, possibly based on some > driver opt-in.. The USB spec does not include any discussion of what things should be done when the system is turned off -- it doesn't even really acknowledge the existence of different system-wide power states. As a result, the USB subsystem never developed any support for power-off callbacks or anything else of the sort. Of course, this kind of thing can always be added. But I don't think there's any way to distinguish (at the USB level) between wakeup from S5-off and wakeup from any other low-power system state. And the PM part of the device model doesn't have multiple types of "enable-wakeup" flags -- either a device is enabled for wakeup or it isn't. Alan Stern
