On 06/22/2014 05:33 PM, Alan Stern wrote: > On Sun, 22 Jun 2014, Wang, Yu wrote: > >> From: "Wang, Yu" <yu.y.wang@xxxxxxxxx> >> >> The system suspend flow as following: >> 1, Freeze all user processes and kenrel threads. >> >> 2, Trying to suspend all devices. >> >> 2.1, If pci device under RPM suspended state, then pci driver will try >> to resume it to RPM active state in prepare stage. >> >> 2.2, xhci_resume function will call usb_hcd_resume_root_hub to queue two >> workqueue items to resume usb2&usb3 roothub devices. >> >> 2.3, Call suspend callbacks of devices. >> >> 2.3.1, All suspend callbacks be called of all hcd's children included >> roothub devices. >> >> 2.3.2, Fianlly, hcd_pci_suspend callback be called. >> >> Due to workqueue threads were already frozen in step 1. So the workqueue >> items can't be scheduled which will cause roothub devices can't be >> resumed in this flow. Then HCD_FLAG_WAKEUP_PENDING flags will not be >> clear which set in usb_hcd_resume_root_hub function. Finally, >> hcd_pci_suspend will return -EBUSY, and system suspend is failed. >> >> The reason why this issue doesn't show up very often, it is due to >> choose_wakeup will be called in step step 2.3.1. In step 2.3.1 >> udev->do_remote_wakeup is not equal device_may_wakeup(&udev->dev), then >> udev will be resume to RPM active for change the wakeup settings. This >> is one be resumed to RPM active to change lucky hit which hides this >> issue. >> >> For some special xHCI controllers which have no USB2 port, then roothub >> will not match hub driver due to probe failed. Then its >> do_remote_wakeup will be set to zero, then will not hit above lucky. >> >> Actually, xhci driver needn't to resume roothub devices everytime like >> above case. It's only needed when there are pending event TRBs. >> >> Signed-off-by: Wang, Yu <yu.y.wang@xxxxxxxxx> > > Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > Thanks, patch added to my for-usb-linus tree. I needed to change xhci_readl() to readl() to get it to compile on newer kernel. Also did some rewording of the commit message, link to patch: https://git.kernel.org/cgit/linux/kernel/git/mnyman/xhci.git/commit/?h=for-usb-linus&id=064aa11e9d06a182dd5637d3224e4f8ac1a59280 -Mathias -- 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
