Hi On 2.3.2021 8.25, Yiyu Zhu wrote: > Hi Mathias, > > I did not set the correct printk value. Here is a recent dmesg showing > the hub connection and disconnection on Linux 5.11.0. > ... > [ 1662.620564] usb usb3: usb wakeup-resume > [ 1662.620570] usb usb3: usb auto-resume > [ 1662.620585] hub 3-0:1.0: hub_resume > [ 1662.620607] hub 3-0:1.0: state 7 ports 2 chg 0002 evt 0000 > [ 1662.620637] usb usb3-port1: over-current change #1 > [ 1662.724578] hub 3-0:1.0: trying to enable port power on non-switchable hub > [ 1662.832221] usb usb3-port1: over-current condition > [ 1662.832237] usb usb3-port1: status 0008, change 0008, 12 Mb/s > [ 1662.832262] hub 3-0:1.0: state 7 ports 2 chg 0000 evt 0000 > [ 1662.832277] hub 3-0:1.0: hub_suspend > [ 1662.832297] usb usb3: bus auto-suspend, wakeup 1 > [ 1662.832307] usb usb3: bus suspend fail, err -16 > [ 1662.832313] hub 3-0:1.0: hub_resume > [ 1662.832344] hub 3-0:1.0: state 7 ports 2 chg 0002 evt 0000 > [ 1662.832363] usb usb3-port1: status 0008, change 0000, 12 Mb/s > [ 1662.832375] hub 3-0:1.0: hub_suspend > [ 1662.832388] usb usb3: bus auto-suspend, wakeup 1 > [ 1662.832397] usb usb3: bus suspend fail, err -16 > [ 1662.832402] hub 3-0:1.0: hub_resume (removed some messages from other buses from above snippet) Looks like the suspend/resume loop is triggered by an over-current event. hub wq notices there is a over-current change, and an over-current status (two separate bits) hub wq clears the change bit, tries to resolve the over-current, fails, and continues. This hub (roothub) has no other children or activity so it runtime suspends. After this the bus tries to suspend, but it fails as xhci bus_suspend() returns -EBUSY if a port is in over-current state. Hub is woken up. hub wq runs, this time there is no over-current change bit set as it was cleared earlier. The over-current status is still active. Hub wq doesn't see any activity, hub is suspended -> try to suspend bus -> fail... Solution is still unclear, maybe hub wq should react to over-current states, not just changes? Thanks Mathias
