On Fri, 19 Sep 2003, David Brownell wrote:
The tricky bits are recovering from "USB suspend" states ... which I suspect usbcore should help with, to minimize the amount of code to write into each HCD. Can't any hub suspend its ports? There are things that are specific to root hubs too, of course.
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.
- Dave
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