[REPOST PATCH 3/3] USB: dwc2: Don't turn off the usbphy in suspend if wakeup is enabled
balbi at ti.com
Mon Jul 6 12:02:12 PDT 2015
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.
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