On Wed, 10 Aug 2016, Baolin Wang wrote: > >> >> For example: No slave attached----> usb interface runtime suspend > >> >> ----> usb device runtime suspend -----> xhci suspend -----> power off > >> >> usb controller. After that if the system wants to enter suspend state, > >> >> then it also will issue usb_dev_suspend(), then the > >> >> pm_runtime_resume() function (issued in choose_wakeup() function) will > >> >> return -ESHUTDOWN due to xhci has been suspend and hardware is not > >> >> accessible. > >> > > >> > Why the controller does not be resumed when the root hub has issued > >> > runtime resume? > >> > >> Because now there is no slave attached, we will not power on usb > >> controller and resume xhci. > >> > > > > I don't know why you set policy like this. Even the controller is > > resumed, it will still be suspended by system suspend. What's more, > > if you disallow it, how can you change your wakeup setting? > > Eg, at runtime suspend, we enable wakeup by default. But for system > > sleep, we disable wakeup by default. > > > > At runtime, if there is no device on the port, even we resumes the > > controller and roohub, it still will be suspended soon. > > For saving power, if there is no slave attached, why we need to power > on usb controller and resume xhci? Especially for mobile device. You need to power-on the USB controller in order to change the wakeup setting. > Moreover the usb device runtime suspend/resume is separate with xhci > suspend/resume, when xhci entered suspend state, only slave attaching > can resume xhci. That's right. Suppose the user wants the system to stay asleep when a slave attaches. But when you suspended the xHCI controller, it was set to wake up when a new slave attaches. So when a slave is attached, the controller will wake up the system. That's bad. If the wakeup setting needs to be changed when the system suspend begins, then you have to power-on the controller to make that change. Given a choice between using a little power or behaving incorrectly, you should choose to use the power. 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
