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I've got a KVM switch from my employer (Aten CS782DP) which works fine as far as I can tell. However, it seems to be causing a problem with my input device (Thinkpad USB Compact Keyboard with TrackPoint) on both Ubuntu 16.04 and 16.10. I'm unable to middle-click anymore and neither can I scroll vertically (horizontally works fine).

In particular, this is how xinput output looks when the keyboard is attached directly:

⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ TPPS/2 IBM TrackPoint                     id=14   [slave  pointer  (2)]
⎜   ↳ Lenovo ThinkPad Compact USB Keyboard with TrackPoint  id=10   [slave  pointer  (2)]
⎜   ↳ ATEN KVM V1.1.104                         id=17   [slave  pointer  (2)]
⎜   ↳ SynPS/2 Synaptics TouchPad                id=13   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated Camera                         id=11   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=12   [slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                    id=15   [slave  keyboard (3)]
    ↳ Lenovo ThinkPad Compact USB Keyboard with TrackPoint  id=9    [slave  keyboard (3)]
    ↳ ATEN KVM V1.1.104                         id=16   [slave  keyboard (3)]

This is how the xinput output looks like when attached throught the KVM:

⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ TPPS/2 IBM TrackPoint                     id=14   [slave  pointer  (2)]
⎜   ↳ Lenovo ThinkPad Compact USB Keyboard with TrackPoint  id=9    [slave  pointer  (2)]
⎜   ↳ Lenovo ThinkPad Compact USB Keyboard with TrackPoint  id=16   [slave  pointer  (2)]
⎜   ↳ SynPS/2 Synaptics TouchPad                id=13   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Video Bus                                 id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ Integrated Camera                         id=11   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=12   [slave  keyboard (3)]
    ↳ ThinkPad Extra Buttons                    id=15   [slave  keyboard (3)]
    ↳ Lenovo ThinkPad Compact USB Keyboard with TrackPoint  id=10   [slave  keyboard (3)]

As far as I can see, this also looks fine except for the weird duplication of the pointer device (IDs 9 and 16). I'm going to assume this has to do with the KVM being a bit like USB hub and ignore this duplication for now.

I've tried running xinput test for both devices and found out that the first device accepts movement and left and right clicks (mouse button 1 and 3), while the second device only horizontal scrolling (button 6 and 7). Neither accepts the middle button (button 2) or vertical scrolling (buttons 4 and 5).

The output of xinput list-props looks identical for both devices:

Device 'Lenovo ThinkPad Compact USB Keyboard with TrackPoint':
    Device Enabled (152):   1
    Coordinate Transformation Matrix (154): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    Device Accel Profile (284): 0
    Device Accel Constant Deceleration (285):   1.000000
    Device Accel Adaptive Deceleration (286):   1.000000
    Device Accel Velocity Scaling (287):    10.000000
    Device Product ID (272):    6127, 24647
    Device Node (273):  "/dev/input/event17"
    Evdev Axis Inversion (288): 0, 0
    Evdev Axes Swap (290):  0
    Axis Labels (291):  "Rel X" (162), "Rel Y" (163), "Rel Horiz Wheel" (282), "Rel Vert Wheel" (283)
    Button Labels (292):    "Button Left" (155), "Button Middle" (156), "Button Right" (157), "Button Wheel Up" (158), "Button Wheel Down" (159), "Button Horiz Wheel Left" (160), "Button Horiz Wheel Right" (161), "Button Side" (280), "Button Extra" (281), "Button Unknown" (275), "Button Unknown" (275), "Button Unknown" (275), "Button Unknown" (275)
    Evdev Scrolling Distance (293): 1, 1, 1
    Evdev Middle Button Emulation (294):    1
    Evdev Middle Button Timeout (295):  50
    Evdev Third Button Emulation (296): 0
    Evdev Third Button Emulation Timeout (297): 1000
    Evdev Third Button Emulation Button (298):  3
    Evdev Third Button Emulation Threshold (299):   20
    Evdev Wheel Emulation (300):    1
    Evdev Wheel Emulation Axes (301):   6, 7, 4, 5
    Evdev Wheel Emulation Inertia (302):    10
    Evdev Wheel Emulation Timeout (303):    200
    Evdev Wheel Emulation Button (304): 2
    Evdev Drag Lock Buttons (305):  0

The default TrackPoint configuration in Ubuntu (/usr/share/X11/xorg.conf.d/11-evdev-trackpoint.conf) looks like this: 

Section "InputClass"
        Identifier      "trackpoint catchall"
        MatchIsPointer  "true"
        MatchProduct    "TrackPoint|DualPoint Stick"
        MatchDevicePath "/dev/input/event*"
        Option  "Emulate3Buttons"       "true"
        Option  "EmulateWheel"  "true"
        Option  "EmulateWheelButton"    "2"
        Option  "XAxisMapping"  "6 7"
        Option  "YAxisMapping"  "4 5"
EndSection

So according to this rule, both devices should get the identical configuration, which is to accept movement, all three buttons and also both types of scrolling. However this is not the case, as illustrated above. A directly attached keyboard works flawlessly.

So what am I missing, what do I need to do to make my external keyboard work properly through this KVM switch?

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  • I have an Aten KVM switch, but a different model. I have not had any problems with it. It may be a problem with the hardware or some firmware, that is difficult to solve. Maybe you can try another keyboard (other brand name and model).
    – sudodus
    Nov 21, 2016 at 18:26

1 Answer 1

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Believe it or not, I've solved this one. The solution is not specific to either the Aten KVM or the Thinkpad Compact keyboard and might help in the generic "my keyboard does not work with a KVM switch properly".

So the idea is this: kernel driver is trying to initialize the specific device (e.g. a keyboard). However, a KVM switch usually provides convenience shortcuts for switching and other features. In case of Aten there is a shortcut for double-click on the scroll wheel. The switch itself needs to filter USB commandos to get this working which obviously intefers with kernel's ability to set certain configuration bits on the device. In my case, it failed to configure the scrolling functionality.

The soluton is simple: disable the conflicting mode. For the Aten, it's called "mouse emulation mode". Having disabled that, everything started working properly.

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