On Tue, 24 Apr 2012, Chen Peter-B29397 wrote: > > But even that won't solve your problem, because Linux can suspend > > individual ports long before suspending the entire USB bus. What > > happens if a port was suspended 2 minutes ago and you want to set the > > PHY to low power now? There's no way to prevent the device on that > > port from sending a wakeup request at a bad time. > > > If only individual port is suspend, but bus does not go to suspend, it is > no problem as the controller is at run mode and the PHY is active, this > resume signal is just port change for hub. I don't think you are right. Suppose an individual port is suspended, and then some minutes later the bus is suspended. Let's say the PHY is set to low power only 2 ms after the bus stops sending SOF packets. Nevertheless, the device attached to the suspended port could send a wakeup signal while the PHY is entering low-power mode. After all, the device has already been suspended for much more than 5 ms. This is very unlikely to happen, but it isn't impossible. Therefore the hardware needs to be able to handle it. 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
