Hi, > Basically the issue comes from hub_port_connect. > > drivers/usb/core/hub.c > > hub_port_init returns -71 -EPROTO and jumps to loop > https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L5450 > > I'd question if usb_ep0_reinit is really required in loop which is > running following functions: > usb_disable_endpoint(udev, 0 + USB_DIR_IN, true); > usb_disable_endpoint(udev, 0 + USB_DIR_OUT, true); > usb_enable_endpoint(udev, &udev->ep0, true); > > this is something only experience over the past decades can tell? > > usb_enable_endpoint will trigger xhci_endpoint_reset which doesn't do > much, but crashes the entire system with the upstream kernel when it > triggers xhci_check_bw_table). > > I removed usb_ep0_reinit here and devices are still workable under > various conditions (again I shorted and pulled D+/D- to ground for > testing). xHCI isn't the only host controller supported by Linux, and usb_ep0_reinit() predates it. Maybe it's pointless today, maybe it isn't, but it's not the root cause of your problem anyway. > The NULL PTR check in xhci_check_bw_table would be a second line > of defense but as indicated in the first mail it shouldn't even get > there. It's an xHCI bug that BW calculation is attempted on an uninitialized device and crashes. Looks like a NULL check somewhere is exactly what is needed, or maybe avoid it completely on EP0 (it's probably no-op). Other similar bug recently: https://lore.kernel.org/linux-usb/D3CKQQAETH47.1MUO22RTCH2O3@xxxxxxxxx/T/#u Yours too should be unique to those Intel Panther Point chipsets. > As a second issue I found in usb_reset_and_verify device > https://github.com/torvalds/linux/blob/master/drivers/usb/core/hub.c#L6131 > > ret = hub_port_init(parent_hub, udev, port1, i, &descriptor); > if (ret >= 0 || ret == -ENOTCONN || ret == -ENODEV) { > break; > } > > hub_port_init can also return -71 / -EPROTO, the cases should be very > rare when usb_reset_and_verify_device is triggered and that happens. Right, and the intent seems to be to simply retry in this case. Regards, Michal
