On Thu, Aug 11, 2016 at 11:08:52AM +0800, Baolin Wang wrote: > Hi Alan, > > On 10 August 2016 at 22:25, Alan Stern <st...@rowland.harvard.edu> wrote: > > 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. > > pm_runtime_resume() function issued in choose_wakeup() can just resume > usb device, which can not power-on the USB controller and resume xHCI. > Cause the user won't know you need to power-on usb controller now, > then how to power-on the USB controller when changing 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. > > OK. But that is a real problem. It will pm_runtime_resume() falied > (issued in choose_wakeup()), cause usb controller has powered-off and > xHCI controller has suspended and we have no method to notify the user > to power-on USB controller. Any good suggestion to solve this, Alan > and Peter? Thanks. >
Maybe you can show us the call stack why pm_runtime_resume has failed at your environment. -- Best Regards, Peter Chen -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
