On Tue, Mar 03, 2020 at 03:05:50PM +0000, Jonas Karlsson wrote: > Hi, > > We have a board with an NXP i.MX8 SoC. We are running Linux 4.19.35 from NXP on the SoC. > > There is a modem connected to the SoC via USB through a USB hub. > The modem presents it self as a cdc-acm device with 4 tty:s. > > Sometimes we end up in a situation where all transfers over USB generetes 'USB transaction Errors". > It is likely that the modem is misbehaving. When this happens we get a lot of "xhci-cdns3: ERROR unknown event type 37" > in the terminal indicating that the xhci event ring is full. This often leads to RCU stalls and sometimes Kernel panics. > > If I enable dynamic debug on xhci_hcd and cdc-acm I can see that all transfers have error code -71 > (-EPROTO which in xhci translates to 'USB transaction error"). When this happens it seems > like xhci resets the ep, sets TR Deq Ptr to unstall the ep and then a new transfer is started > which also fails. This behavior generates a lot of events on the event ring which causes > 'ERROR unknown event type 37'. This loop of failing transfers seems to continue until we either unbind > the USB driver or get a kernel panic. The SoC almost becomes unresponsive since it spends most of the > time executing usb interrupts. > > If I pull the reset pin of the USB hub and keep it in reset state at this point, the event loop of failing > transfers continues despite there is nothing on the USB bus any longer. The only way to get out of > that loop is to either unbind the usb driver or power cycle the board. > > Is this the expected behavior when USB transaction error happens for all transfers when using cdc-acm class driver? > Or could there be something wrong in the low level USB driver (Cadence in our case)? We need to figure out why we > get all the transaction errors but we also need to make sure the kernel does not die on us when we have a misbehaving USB device. > Does anyone have a suggestion on what we could do to improve the stability of the kernel in this situation? I would blame the xhci-cdns driver as it is the one controlling all of this. I don't see this driver in the 4.19 tree, so I think you are going to have to get support from the company that provided you with that driver as you are already paying for that support from them :) good luck! greg k-h
