On Mon, Jul 06, 2015 at 02:58:16PM -0400, Alan Stern wrote: > On Mon, 6 Jul 2015, Douglas Anderson wrote: > > > If the 'snps,need-phy-for-wake' is set in the device tree then: > > > > - We know that we can wakeup, so call device_set_wakeup_capable(). > > The USB core will use this knowledge to enable wakeup by default. > > - We know that we should keep the PHY on during suspend if something > > on our root hub needs remote wakeup. This requires the patch (USB: > > Export usb_wakeup_enabled_descendants()). Note that we don't keep > > the PHY on at suspend time if it's not needed because it would be a > > power draw. > > You know, this is the first time I've run across this optimization. > > In principle it applies to any USB host controller, not just to PHYs. > There's no reason to enable wakeup for a controller if none of the > attached devices can issue a wakeup request. > > I don't know if implementing this in other HCDs would save any power. > Any ideas? most likely it would. Enabling wakeup usually boils down to keeping a tiny part of the controller (or PHY) powered up. Sometimes that lies in an always-on power domain, so there would be no difference. cheers -- balbi
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