On Tue, 17 Jul 2012, Oliver Neukum wrote: > > Yeah. Lost some background introduction. I recently try to realize usb > > port power off mechanism for ports with device. So design, the port with > > device only can be power off when remote wakeup disable. Why is that? What happens if you power-off a port where the device has remove wakeup enabled? > > But I found > > remote wakeup was entirely control by driver and userspace has no > > control. needs_remote_wakeup is set to 1 when the device is opened. What sort of driver are you talking about? An HID driver? Serial driver? > But the driver will not work if you don't use remote wakeup when it needs it. > Under those circumstances you better unbind the driver. > > > So that means the device's remote wakeup can not be disabled and usb > > port can not be powered off. So I try to provide a control of remote > > wakeup to userspace. When system becomes idle such as blank screen, > > some usb devices may be able to disable remote wakeup and power off. > > Yes, this is an unsoved problem. But the approach is no good. Don't > disable remote wakeup behind the driver's back. Tell the driver that a reduced > level of service is acceptable. The best way to do this might depend on the driver. But in general, if a driver needs wakeup in order to work properly then it _won't_ work when the port is powered off. So as Oliver says, the user might as well unbind the driver first. Alan Stern -- 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
