Problem Summary: Problem has been observed generally with PM states where VBUS goes off during suspend. There are some SS USB devices which take longer time for link training compared to many others. Such devices fail to reconnect with same old address which was associated with it before suspend. When system resumes, at some point of time (dpm_run_callback-> usb_dev_resume->usb_resume->usb_resume_both->usb_resume_device-> usb_port_resume) SW reads hub status. If device is present, then it finishes port resume and re-enumerates device with same address. If device is not present then, SW thinks that device was removed during suspend and therefore does logical disconnection and removes all the resource allocated for this device. Now, if I put sufficient delay just before root hub status read in usb_resume_device then, SW sees always that device is present. In normal course(without any delay) SW sees that no device is present and then SW removes all resource associated with the device at this port. In the latter case, after sometime, device says that hey I am here, now host enumerates it, but with new address. Problem had been reproduced when I connect verbatim USB3.0 hard disc with my STiH407 XHCI host running with 3.10 kernel. I see that similar problem has been reported here. https://bugzilla.kernel.org/show_bug.cgi?id=53211 Reading above it seems that bug was not in 3.6.6 and was present in 3.8 and again it was not present for some in 3.12.6, while it was present for few others. I tested with 3.13-FC19 running at i686 desktop, problem was still there. However, I was failed to reproduce it with 3.16-RC4 running at same i686 machine. I would say it is just a random observation. Problem for few devices is always there, as I am unable to find a proper fix for the issue. So, now question is what should be the amount of delay so that host is always able to recognize suspended device after resume. XHCI specs 4.19.4 says that when Link training is successful, port sets CSC bit to 1. So if SW reads port status before successful link training, then it will not find device to be present. USB Analyzer log with such buggy devices show that in some cases device switch on the RX termination after long delay of host enabling the VBUS. In few other cases it has been seen that device fails to negotiate link training in first attempt. It has been reported till now that few devices take as long as 2000 ms to train the link after host enabling its VBUS and RX termination. This patch implements a 2000 ms timeout for CSC bit to set ie for link training. If in a case link trains before timeout, loop will exit earlier. This patch implements above delay, but only for SS device and when persist is enabled. So, for the good device overhead is almost none. While for the bad devices penalty could be the time which it take for link training. But, If a device was connected before suspend, and was removed while system was asleep, then the penalty would be the timeout ie 2000 ms. Results: Verbatim USB SS hard disk connected with STiH407 USB host running 3.10 Kernel resumes in 461 msecs without this patch, but hard disk is assigned a new device address. Same system resumes in 790 msecs with this patch, but with old device address. Cc: <stable@xxxxxxxxxxxxxxx> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Pratyush Anand <pratyush.anand@xxxxxx> --- Changes since RFC: -- Loop implementation updated as per Alan's comment -- Commit log updated as per observation with different failing devices. drivers/usb/core/hub.c | 41 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+) diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index 88f1db2..f0c2fda 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -3259,6 +3259,43 @@ static int finish_port_resume(struct usb_device *udev) } /* + * There are some SS USB devices which take longer time for link training. + * XHCI specs 4.19.4 says that when Link training is successful, port + * sets CSC bit to 1. So if SW reads port status before successful link + * training, then it will not find device to be present. + * USB Analyzer log with such buggy devices show that in some cases + * device switch on the RX termination after long delay of host enabling + * the VBUS. In few other cases it has been seen that device fails to + * negotiate link training in first attempt. It has been + * reported till now that few devices take as long as 2000 ms to train + * the link after host enabling its VBUS and termination. Following + * routine implements a 2000 ms timeout for link training. If in a case + * link trains before timeout, loop will exit earlier. + * + * FIXME: If a device was connected before suspend, but was removed + * while system was asleep, then the loop in the following routine will + * only exit at timeout. + * + * This routine should only be called when persist is enabled for a SS + * device. + */ +static int wait_for_ss_port_enable(struct usb_device *udev, + struct usb_hub *hub, int *port1, + u16 *portchange, u16 *portstatus) +{ + int status = 0, delay_ms = 0; + + while (delay_ms < 2000) { + if (status || *portstatus & USB_PORT_STAT_CONNECTION) + break; + msleep(20); + delay_ms += 20; + status = hub_port_status(hub, *port1, portstatus, portchange); + } + return status; +} + +/* * usb_port_resume - re-activate a suspended usb device's upstream port * @udev: device to re-activate, not a root hub * Context: must be able to sleep; device not locked; pm locks held @@ -3354,6 +3391,10 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg) } } + if (udev->persist_enabled && hub_is_superspeed(hub->hdev)) + status = wait_for_ss_port_enable(udev, hub, &port1, &portchange, + &portstatus); + status = check_port_resume_type(udev, hub, port1, status, portchange, portstatus); if (status == 0) -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html