On 05.11.18 16:35, Mathias Nyman wrote: > On 26.10.2018 17:07, Alan Stern wrote: >> On Fri, 26 Oct 2018, Dennis Wassenberg wrote: >> >>>>> --- a/drivers/usb/core/hub.c >>>>> +++ b/drivers/usb/core/hub.c >>>>> @@ -2815,7 +2815,9 @@ static int hub_port_reset(struct usb_hub *hub, int port1, >>>>> USB_PORT_FEAT_C_BH_PORT_RESET); >>>>> usb_clear_port_feature(hub->hdev, port1, >>>>> USB_PORT_FEAT_C_PORT_LINK_STATE); >>>>> - usb_clear_port_feature(hub->hdev, port1, >>>>> + >>>>> + if (!warm) >>>>> + usb_clear_port_feature(hub->hdev, port1, >>>>> USB_PORT_FEAT_C_CONNECTION); >>>>> /* >>>> >>>> The key fact is that connection events can get lost if they happen to >>>> occur during a port reset. >>> Yes. >>>> >>>> I'm not entirely certain of the logic here, but it looks like the >>>> correct test to add should be "if (udev != NULL)", not "if (!warm)". >>>> Perhaps Mathias can confirm this > > Sorry about the late response, got distracted while performing git > archeology. > > "if (udev != NULL)" would seem more reasonable. > > Logs show that clearing the FEAT_C_CONNECTION was originally added > after a hot reset failed, and before issuing a warm reset to a SS.Inactive > link. (see 10d674a USB: When hot reset for USB3 fails, try warm reset.) > > Apparently all the change flags needed to be cleared for some specific > host + device combination before issuing a warm reset for the enumeration > to work properly. > > The change to always clear FEAT_C_CONNECTION for USB3 was done later in patch: > a24a607 USB: Rip out recursive call on warm port reset. > > Motivation was: > > "In hub_port_finish_reset, unconditionally clear the connect status > change (CSC) bit for USB 3.0 hubs when the port reset is done. If we > had to issue multiple warm resets for a device, that bit may have been > set if the device went into SS.Inactive and then was successfully warm > reset." > >>> I don't know if clearing the USB_PORT_FEAT_C_CONNECTION bit is >>> correct in case of a non warm reset. In my case I always observed a >>> warm reset because of the link state change. >>> Thats why I checked the warm variable to not change the behavoir for >>> cases a didn't checked for the first shot. >> >> (The syntax of that last sentence is pretty mangled; I can't understand >> it.) >> >> Think of it this way: >> >> If a device was not attached before the reset, we don't want >> to clear the connect-change status because then we wouldn't >> recognize a device that was plugged in during the reset. >> >> If a device was attached before the reset, we don't want any >> connect-change status which might be provoked by the reset to >> last, because we don't want the core to think that the device >> was unplugged and replugged when all that happened was a reset. >> >> So the important criterion is whether or not a device was attached to >> the port when the reset started. It's something of a coincidence that >> you only observe warm resets when there's nothing attached. >> >>> During the first run of usb_hub_reset the udev is NULL because in >>> this situation the device is not attached logically. >>> >>> [ 112.889810] usb 4-1-port1: XXX: port_event: portstatus: 0x2c0, portchange: 0x40! >>> [ 113.201192] usb 4-1-port1: XXX: hub_port_reset: udev: (nil)! >>> [ 113.201198] usb 4-1-port1: XXX: hub_port_reset (not clearing USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x1! >>> [ 113.253612] usb 4-1-port1: XXX: port_event: portstatus: 0x203, portchange: 0x1! >>> [ 113.377208] usb 4-1-port1: XXX: hub_port_reset: udev: ffff88046b302800! >>> [ 113.377214] usb 4-1-port1: XXX: hub_port_reset (not clearing USB_PORT_FEAT_C_CONNECTION): 0x203, portchange: 0x0! >>> [ 113.429478] usb 4-1.1: new SuperSpeed USB device number 7 using xhci_hcd >>> [ 113.442370] usb 4-1.1: New USB device found, idVendor=0781, idProduct=5596 >>> [ 113.442376] usb 4-1.1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 >>> [ 113.442381] usb 4-1.1: Product: Ultra T C >>> [ 113.442385] usb 4-1.1: Manufacturer: SanDisk >>> [ 113.442388] usb 4-1.1: SerialNumber: 4C530001131013121031 >>> >>> Or maybe we can skip clearing the USB_PORT_FEAT_C_CONNECTION bit in >>> case of hub_port_reset completely without any other check? >> >> See above. > > Checking for udev sounds reasonable to me. > Not sure if we should worry about the specific host+device combo that needed flags > cleared before warm reset. See patch: > > 10d674a USB: When hot reset for USB3 fails, try warm reset. > https://marc.info/?l=linux-usb&m=131603549603799&w=2 > > -Mathias Checking for udev works well too in my case. So there is no need to check the warm flag. Regarding the other point about the specific host+device combo which needs the flags cleared, I don't know how to proceed. Best regards, Dennis
