On 2014年11月24日 23:33, Alan Stern wrote:
On Mon, 24 Nov 2014, Lu, Baolu wrote:Hi Mathias, Alan and all, During xhci handling a completion event for stop endpoint command , xhci_handle_cmd_stop_ep() always gives back a urb with status set to 0. The comment says, /* Doesn't matter what we pass for status, since the core will * just overwrite it (because the URB has been unlinked). */ I don't think this assumption is always correct. Stop endpoint command is used in below two cases in xhci driver. 1. In xhci_urb_dequeue(). This is the hcd driver interface for canceling a transfer. 2. During suspend process. This is to stop on-going transfers and cause xHC to save various endpoint state into memory. The assumption of "URB has been unlinked" is only the fact for case 1. It's wrong in case 2. If my understanding is right, USB client drivers (serial, mass storage ....) might receive an incompletion urb transfer with status set to success during suspend/resume. Please correct me if there is any misunderstanding.When a suspend is about to occur, usbcore makes sure there are no outstanding URBs for the device. It tells the device's driver to go into suspend, unlinks any remaining URBs, and prevents new ones from being submitted.
That's clear now. Thank you, Alan.
Alan Stern
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