On Sun, 26 Sep 2004, David Brownell wrote: > I think some of the definitions are system-specific, and all of the > relevant specifications are weasel-worded to support that. Key > point: if RAM is powered, some devices could be too; and the > wakeup devices (USB, network, keyboard, etc) probably need it.
So you're saying that I need to add a fourth power level to my scheme, call it STR, between Low and Off. Some drivers might implement STR the same as Low, others might implement it the same as Off. Calling these things power levels is no longer appropriate. "Logical power level" would be a better term. > > > There can be whole trees of devices sitting in USB suspend state, which > > > will be enabled just fine by correctly resuming the tree. Heck, one of > > > them may have just woken the system up ... :) > > > > Not from a suspend-to-disk! :-) > > Why not? A particular implementation of STD might not support it. > But most motherboards today consume power when "off", and some > allocate power to USB specifically to support those wakeup modes. Okay. But... > > So resume-from-disk requires detecting, initializing, and enumerating > > every USB device, pretty much like usb_reset_device() does now. > > Only on boards that don't provide USB suspend current. > Or where Linux can't leverage it, because ACPI or BIOS > support is lacking. Let's suppose there is USB suspend current available during STD. How does the kernel know that the current wasn't interrupted while power was off? If the USB drivers are linked into the kernel, what happens when they start initializing devices during the resume-from-disk bootup? What about the early-HC-disable patch that was recently added? Even if we can get away without initializing and enumerating devices under favorable conditions, the code to do it still has to be there in order to handle unfavorable conditions. Since the code has to be there, why not use it for resume-from-power-off? Alan Stern ------------------------------------------------------- This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170 Project Admins to receive an Apple iPod Mini FREE for your judgement on who ports your project to Linux PPC the best. Sponsored by IBM. Deadline: Sept. 24. Go here: http://sf.net/ppc_contest.php _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
