On Wed, 25 Aug 2004, David Brownell wrote: > When to power back up is an interesting issue, and it sounded > like you had a procedure in mind that could handle that well > in certain common cases.
I didn't. But having khubd do it during the logical disconnect processing seems like the logical choice. > > How would you handle hubs with ganged power control? (Or even no power > > control?) Just skip the power-off step, with a log message? > > Ganged power switches should have power turned off at least > during initialization, in the best of all worlds. They'll run for a > long time ... so at most one init-time message. "They" refers to the power switches? What do you mean, the switches will run for a long time? Do you mean the power will be on for a long time? Or do you mean that the hubs will run for a long time? And what does that have to do with turning off power for a logical disconnect? What sort of init-time message -- the kind that the khubd debugging code already writes, noting that the power switches are ganged? What about logical disconnects happening after init-time? (Sorry to go on like that, but sometimes I just don't follow what you are saying...) > I don't think > there would be cases where power-off is "needed" and not > possible, except (a) devices craving VBUS cycles, which we > may not even be able to detect without cycling it!, and > (b) requests from users [power/state set to ACPI D3], where > the Linux PM model says ISTR that to suspend as deeply > as possible and report no error [D2 not D3]. (b) wouldn't involve a logical disconnect, but (a) would. Of course, we don't have any way to do (a) at all right now -- apart from asking the user to unplug the USB cable! > You're right that if per-port switching isn't available (restricted to > root hubs, I think) that's potential trouble. I guess I'd think the > answer is to use it where it's available (making devices that > need VBUS cycled, or links which use SRP, happier), but not rely > on it in all cases. So do it if we can, otherwise don't worry about it. Alan Stern ------------------------------------------------------- SF.Net email is sponsored by Shop4tech.com-Lowest price on Blank Media 100pk Sonic DVD-R 4x for only $29 -100pk Sonic DVD+R for only $33 Save 50% off Retail on Ink & Toner - Free Shipping and Free Gift. http://www.shop4tech.com/z/Inkjet_Cartridges/9_108_r285 _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
