On Thu, Mar 28, 2013 at 07:58:47AM +0800, Lan Tianyu wrote: > On 2013/3/28 2:47, Alan Stern wrote: > >On Thu, 28 Mar 2013, Lan Tianyu wrote > >What happens if there's no device plugged in to the port, but the hub > >is enabled for remote wakeup? How will the hub be able to detect a > >plug-in event if the port isn't powered? > > > >Alan Stern > > > Hi Alan: > Great thanks for your review. > The hub will not detect the new devices. From my opinion, this > depends on the user space since the port only will be powered off when > pm qos NO_POWER_OFF flag is unset(it is default to be set). If unset > the flag, losing plug-in event should have been took into account. So basically, you're saying that any new distro policy that turns off port power will need to re-enable it if the user wants hotplug events from a hub? I think that's a very important thing to document. I really think we need to add more description about the port power off mechanisms to Documentation/usb/power-management.txt. There's a little bit in Documentation/ABI/testing/sysfs-bus-usb, but since this mechanism is so new, I think we need to educate distro users on its effects and suggestions on how to use it. Can you take a first stab at an overview, and I'll let you know what's missing? Sarah Sharp -- 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
