* Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> [150318 18:51]: > On Wed, 18 Mar 2015, Tony Lindgren wrote: > > > > If the host controller is started more than once, you will end up > > > unregistering and re-registering the root hub. The device core does > > > not allow this. Once a device has been unregistered, you must not try > > > to register it again -- you have to allocate a new device and register > > > it instead. > > > > > > Also, although you call the driver's ->start method multiple times, the > > > ->reset method is called only once, when the controller is first > > > probed. It's not clear that this will work in a situation where the HC > > > and the UDC share hardware state; after the UDC is stopped it may be > > > necessary to reset the HC before it can run again. > > > > > > It might be possible to make this work, but I suspect quite a few > > > drivers would need rewriting first. As another example of the problems > > > you face, consider how stopping a host controller will interact with > > > the driver's PM support (both system suspend and runtime suspend). > > > > > > It would be a lot simpler to unbind the host controller driver > > > completely when switching to device mode and rebind it when switching > > > back. I guess that is the sort of heavy-duty approach you want to > > > avoid, but it may be the only practical way forward. > > > > Hmm from memory I think the OTG spec assumes the USB devices are > > suspended when attempting the role change? I could be totally wrong, > > it's been a really long time since I've looked at the OTG spec, but > > maybe that would make it easier to deal with thing? > > This patch deals with the host side, not the device side. The fact > that the device is suspended is not relevant to the issues above. OK, got it. > Besides, the problems I outlined are more connected with the way > Linux's host-side USB stack is organized, and not so much with the > details of the OTG spec. Yes thanks for the explanation. Regards, Tony -- 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
