On Tue, 23 Sep 2003, David Brownell wrote: > Alan Stern wrote: > > > > Sure, a hub (including a virtual root hub) can suspend any of its ports, > > independently. But there's currently no provision in the system for doing > > that. Besides, I think there's a difference between telling an HC to > > suspend each one of its ports and telling it to go into a global suspend > > mode. > > That was my point ... no provision in usbcore! Specifically, the hub > driver doesn't think about such stuff. And "global suspend" is a UHCI > specific term. How is that different (is it?) from suspending all ports > on that particular (== not "global"!) root hub? I thought it wouldn't > need to be visible outside of the UHCI code. > > Both EHCI and OHCI should help PM to a limited extent, by turning off > the portions of the schedule (periodic, and control/bulk) that aren't > in use ... so the HC does as little DMA as possible. But they won't > go any further at the moment; neither will any individual USB drivers.
Global suspend is the UHCI equivalent of what you say EHCI and OHCI do automatically: the controller doesn't run and it doesn't do DMA. That's different from suspending individual ports. When a port is suspended, the USB signals are still sent to the other ports and the controller is still active. Even if all the ports are suspended, the UHCI controller is still active and scanning the schedule. There's no way to disable any parts of that DMA; it's either all the way on or all the way off. While it might be nice to have usbcore tell hubs to suspend ports that haven't been used for some period of time (a good power savings for bus-powered devices), it doesn't seem especially critical at the moment. Alan Stern ------------------------------------------------------- This sf.net email is sponsored by:ThinkGeek Welcome to geek heaven. http://thinkgeek.com/sf _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
