DisplayLink Forum - Issue with DisplayLink Ethernet speeds

Hi,

I've been debugging a issue this week where the DisplayLink USB network in my docking station wouldn't do much more than 400mbit/s download on a 1gbit/s capable network. On a windows device it worked no problem, but if you were running Linux the speed would drop right down.

After a lot of trial and error, I've found the cause of the problem, at least in the case of my Toshiba docking station, both single and dual screen model of docks are affected.

The udev rules that sets `cdc_ncm/rx_max` and `cdc_ncm/tx_max` to the correct max values, doesn't fire on my docking station, because the value of ENV{PRODUCT} is blank and does not start with "17e9/*". I then added a different version of the cdc_ncm rules to detect the DisplayLink driver differently, so it doesn't apply the rule to non DisplayLink docks. to use VENDOR ID instead of PRODUCT

Code:

ACTION=="add|move|bind", SUBSYSTEM=="net", DRIVERS=="cdc_ncm", ENV{ID_USB_VENDOR_ID}=="17e9", \

    ATTR{cdc_ncm/rx_max}=="?*", ATTR{cdc_ncm/dwNtbInMaxSize}=="?*", ATTR{cdc_ncm/rx_max}="$attr{cdc_ncm/dwNtbInMaxSize}"

ACTION=="add|move|bind", SUBSYSTEM=="net", DRIVERS=="cdc_ncm", ENV{ID_USB_VENDOR_ID}=="17e9", \

    ATTR{cdc_ncm/tx_max}=="?*", ATTR{cdc_ncm/dwNtbOutMaxSize}=="?*", ATTR{cdc_ncm/tx_max}="$attr{cdc_ncm/dwNtbOutMaxSize}"

I add this outside of the `ENV{PRODUCT}!="17e9/*", GOTO="not_dl"` and `LABEL="not_dl"` lines of the rules file created by displaylink-driver-6.3.0-48.run, so effectively at the end of the current udev rule file.

Hopefully this issue can be fixed in the installer you provide, no doubt other users are having this issue with the current way the rules are, which is failing to apply the corrected values

If it helps this is the udevadm info for my dock's ethernet

udevadm info --query=property --path=/sys/class/net/eth0

Code:

DEVPATH=/devices/pci0000:00/0000:00:08.1/0000:74:00.4/usb4/4-1/4-1.1/4-1.1:1.5/net/eth0

INTERFACE=eth0

IFINDEX=12

SUBSYSTEM=net

USEC_INITIALIZED=3640388761

ID_NET_DRIVER=cdc_ncm

ID_BUS=usb

ID_MODEL=dynadock_U3.0

ID_MODEL_ENC=dynadock\x20U3.0

ID_MODEL_ID=4305

ID_SERIAL=DisplayLink_dynadock_U3.0_10084571

ID_SERIAL_SHORT=10084571

ID_VENDOR=DisplayLink

ID_VENDOR_ENC=DisplayLink

ID_VENDOR_ID=17e9

ID_REVISION=3015

ID_TYPE=generic

ID_USB_MODEL=dynadock_U3.0

ID_USB_MODEL_ENC=dynadock\x20U3.0

ID_USB_MODEL_ID=4305

ID_USB_SERIAL=DisplayLink_dynadock_U3.0_10084571

ID_USB_SERIAL_SHORT=10084571

ID_USB_VENDOR=DisplayLink

ID_USB_VENDOR_ENC=DisplayLink

ID_USB_VENDOR_ID=17e9

ID_USB_REVISION=3015

ID_USB_TYPE=generic

ID_USB_INTERFACES=:ff0003:fe0101:010120:010220:020d00:0a0001:

ID_USB_INTERFACE_NUM=05

ID_USB_DRIVER=cdc_ncm

ID_USB_CLASS_FROM_DATABASE=Miscellaneous Device

ID_USB_PROTOCOL_FROM_DATABASE=Interface Association

ID_VENDOR_FROM_DATABASE=DisplayLink

ID_NET_NAMING_SCHEME=v258

ID_NET_NAME_MAC=enx0050b65b7c2b

ID_OUI_FROM_DATABASE=GOOD WAY IND. CO., LTD.

ID_NET_NAME_PATH=enp116s0f4u1u1i5

ID_MM_CANDIDATE=1

ID_PATH_WITH_USB_REVISION=pci-0000:74:00.4-usbv3-0:1.1:1.5

ID_PATH=pci-0000:74:00.4-usb-0:1.1:1.5

ID_PATH_TAG=pci-0000_74_00_4-usb-0_1_1_1_5

ID_NET_LINK_FILE=/usr/lib/systemd/network/99-default.link

ID_NET_NAME=eth0

SYSTEMD_ALIAS=/sys/subsystem/net/devices/eth0

TAGS=:systemd:

CURRENT_TAGS=:systemd:

Any more questions, I'll be happy to answer.