> On Mar 30, 2020, at 2:41 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, 30 Mar 2020, John Donnelly wrote: > >> Hi, >> >> >> I discovered this particular server doesn’t continue probing the >> ports behind BCM is due to iommu being on. >> >> With “ iommu=on “ >> >> USB Initialization stops after the BCM " 3:1.0 hub with 2 ports >> detected” , but no additional probing is done to discover the other >> end-points behind 3:1.0 : >> >> >> [ 9.467008] hub 2-1:1.0: 8 ports detected >> [ 9.538361] usb 4-3: new high-speed USB device number 2 using xhci_hcd >> [ 9.564504] usb 4-3: New USB device found, idVendor=0424, idProduct=2660, bcdDevice= 8.01 >> [ 9.580454] usb 4-3: New USB device strings: Mfr=0, Product=0,SerialNumber=0 >> [ 9.596642] hub 4-3:1.0: USB hub found >> [ 9.611040] hub 4-3:1.0: 2 ports detected. >> >> ** NO ADDITIONAL DISCOVERY ** >> >> >> >> 2. With intel_iommu=off, the BCM ports are probed after " 3:1.0: 2 >> ports detected " state: >> >> [ 5.705072] usb 3-1: new full-speed USB device number 2 using uhci_hcd >> [ 5.772363] usb 4-3: new high-speed USB device number 2 using xhci_hcd >> [ 5.800528] usb 4-3: New USB device found, idVendor=0424, idProduct=2660,bcdDevice= 8.01 >> [ 5.816439] usb 4-3: New USB device strings: Mfr=0, Product=0, SerialNumber=0 >> [ 5.832298] hub 4-3:1.0: USB hub found >> [ 5.845786] hub 4-3:1.0: 2 ports detected. <---- AFTER THIS WE CONTINUE TO PROBE >> [ 5.889503] usb 3-1: New USB device found, idVendor=03f0, idProduct=7029, bcdDevice= 0.02 >> [ 5.905380] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=0 >> [ 5.920997] usb 3-1: Product: Virtual Keyboard >> [ 5.934493] usb 3-1: Manufacturer: BMC >> >> >> What prompts the discovery to look beyond : "hub 4-3:1.0: 2 ports >> detected. “ ? Could there some state that needs examined before it >> continues ? ( I’ve never dealt with USB before on Linux ) . > > Were there any differences between your two tests other than the iommu > setting? No ! > >> The end result is the usbhid devices ( kdb and mouse ) are found : >> >> /: Bus 05.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/6p, 5000M >> /: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/15p, 480M >> |__ Port 3: Dev 2, If 0, Class=Hub, Driver=hub/2p, 480M >> /: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=uhci_hcd/2p, 12M >> |__ Port 1: Dev 2, If 0, Class=Human Interface Device, Driver=usbhid, 12M >> |__ Port 1: Dev 2, If 1, Class=Human Interface Device, Driver=usbhid, 12M >> /: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M >> |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M >> /: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M >> >> >> Is there a way I can turn on debug messages for the usb driver(s) to >> increase verbosity during boot since these are build-in modules ? > > You can turn on kernel debugging for USB during boot-up by manually > adding: > > dyndbg="module usbcore =p" > > to the boot command line. (See the file > Documentation/admin-guide/dynamic-debug-howto.rst in the kernel source > for an explanation.) The debugging messages will then appear in the > output from the dmesg command. > > It might be even more enlightening to collect a couple of usbmon > traces. (See Documentation/usb/usbmon.rst.) Here's what you should > do, first with iommu=on and then again with iommu=off. After booting, > as root: > > echo 0 >/sys/bus/usb/devices/usb3/bConfigurationValue > cat /sys/kernel/debug/usb/usbmon/3u >mon-on.txt & > echo 1 >/sys/bus/usb/devices/usb3/bConfigurationValue > fg > ... wait a few seconds ... > ^C > > For the iommu=off test, replace the "mon-on.txt" with "mon-off.txt" > (this is the name of the file where the usbmon trace will be stored -- > you can use other names if you want). Then attach the two trace > files to your next email message. > > Alan Stern > Thanks for the hints ! I will probe around more !
