On Wed, Sep 26, 2012 at 05:31:43PM +0200, Oliver Neukum wrote: > Hi Sarah, > > watching your talk and drinking tea I had an idea. > > Switching off ports saves power in itself. It also allows > switching off host controllers. > The problem with switching off power on external ports is that they > don't detect hotplug events anymore. > > So is there a way to switch off controllers and leave ports on, saving > at least some power? That sounds awfully like host/bus suspend. :) Or if you're talking about completely powering off the host, a D3 cold mechanism for the PCI host controller. > And it seems to me that in many cases, namely > EHCI with companion controllers and XHCI controllers that implement > a vendor specific switching option, we could switch the ports so that > a minimum number of controllers is connected to ports that are not switched > off. It would be nice to have only one powered host controller, I agree. But I'm not sure the idea would actually help systems with the EHCI/xHCI port switching. We would want to leave any powered port under the xHCI host controller, because we want USB 3.0 devices to connect at SuperSpeed. If we can't switch over the EHCI ports to xHCI, it's either because there isn't a physical switch, or the OEM is preventing the port switchover because it has some internal USB device that doesn't work well under xHCI. So we're forced into having two powered host controllers, and there's no other way we can switch ports to help. I think you run into similar issues with EHCI hosts with companion controllers. You want all the powered ports to be under EHCI by default. If you have a port under UHCI or OHCI, then it's because you have a connected LS/FS device. So you're stuck with an two powered host controllers. Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
