Tips for diagnosing ghost arrow key presses with USB keyboard?

Tips for diagnosing ghost arrow key presses with USB keyboard?

[David Wilson]

Hi all,

I realize this might be slightly off-topic here but I figured it wouldn't hurt to give it a shot:

On a laptop where I have an up-to-date Guix System installation, I use an external USB keyboard while docked at my desk. With the keyboard plugged in, I'm experiencing an annoying issue where there are occasional ghost keypresses of the RIGHTARROW key. Using xev and evtest I've narrowed it down to events coming from the USB device itself, presumably originating from the kernel driver. I experience these keypresses both in a tty and in Xorg sessions. When the USB keyboard isn't plugged in, everything works perfectly.

There doesn't seem to be any clear trigger that causes this issue so I'm having trouble making further progress in fixing it. Anyone know of any other tricks I could try to diagnose or alleviate the problem? If you have a good resource for poking around with kernel drivers, I'd be willing to go that route to see if it's a legitimate bug in the kernel.

Thanks!

David

Re: Tips for diagnosing ghost arrow key presses with USB keyboard?

[Tobias Geerinckx-Rice]

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David,

David Wilson 写道：
> There doesn't seem to be any clear trigger that causes this 
> issue so I'm having trouble making further progress in fixing 
> it. Anyone know of any other tricks I could try to diagnose or 
> alleviate the problem? If you have a good resource for poking 
> around with kernel drivers, I'd be willing to go that route to 
> see if it's a legitimate bug in the kernel.

I don't know which kernel driver (HCI or input) you suspect and 
can't be of much help with their design, but I have had some 
success using usbmon[0] to sniff the wire.  It's available in 
Guix.

What kind of keyboard is this?

Linux provides some support for ‘special’ devices under:

  -> Device Drivers
    -> HID support
      -> HID bus support
        -> Special HID drivers

For example:

  CONFIG_HID_APPLE:
  Support for some Apple devices which less or more break
  HID specification.
  Say Y here if you want support for keyboards of Apple iBooks,
  PowerBooks, MacBooks, MacBook Pros and Apple Aluminum.

That seems to describe yours if it's not simply broken :-)

Looks like most/all of these specific modules are built by Guix, 
but maybe not loaded?

Hoping to have been of some service,

T G-R

[0]: https://www.kernel.org/doc/html/latest/usb/usbmon.html

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Re: Tips for diagnosing ghost arrow key presses with USB keyboard?

[David Wilson]

Thanks for the ideas Tobias!

The specific keyboard is the "ThinkPad Compact USB Keyboard with Trackpoint" which seems to be supported by the "hid-lenovo" driver:

https://github.com/torvalds/linux/blob/master/drivers/hid/hid-lenovo.c

lsmod tells me that it's loaded in my system and dmesg seems to indicate that the "lenovo" driver is being used when the device gets plugged in.  

On Fri, Nov 8, 2019, at 10:10 AM, Tobias Geerinckx-Rice wrote:
> I don't know which kernel driver (HCI or input) you suspect and 
> can't be of much help with their design, but I have had some 
> success using usbmon[0] to sniff the wire.  It's available in 
> Guix.
>

I'll certainly give usbmon a shot, thanks for the tip!  I found this resource which got me started with it pretty easily:

https://www.kernel.org/doc/html/latest/usb/usbmon.html

Now I just have to decipher the log output :)

Thanks!

David