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. -- Baolin.wang Best Regards -- 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
