Detecting the used keyboard driver

Matthew Garrett mjg59 at
Thu Apr 30 11:20:13 PDT 2009

On Thu, Apr 30, 2009 at 08:09:01PM +0200, Marvin Raaijmakers wrote:
> Well a scancode is for the kernel like what a X keycode is to the X
> server, and a kernel keycode is for the kernel what a key symbol is to
> the X server. So when you change the kernel keycode of a key, then the
> X server will receive another kernel keycode from the kernel and as a
> result the key will have another X keycode. So an X keycode is not
> fixed for a specific key. Furthermore some keys will not have a kernel
> keycode by default and such keys won't work under X (because the X
> server doesn't receive anything about these keys from the kernel).
> Believe me I've thought about this ;)

For a given kernel keycode and a given X keyboard driver, the X keycode 
will always be the same. If you're setting the scancode to the canonical 
kernel keycode that'll be a meaningful transformation. So you could just 
add those X keycodes to the pc105 keymap, since they're already present 
in the evdev keymap and so will already produce the correct keysyms with 
the evdev driver. For example:

Scancode e007 will be the battery key scancode on a Dell. This will map 
to kernel keycode 236 (KEY_BATTERY). kbd will read this as e044 and 
translate it into X keycode 204. evdev will read this as 236 and (I 
/think/ - I can't remember if the +8 mapping is still relevant for 
evdev) translate it into X keycode 244.

As long as the kernel keycode is KEY_BATTERY, the X keycode will depend 
only on whether kbd or evdev is in use. evdev will always use the evdev 
keymap and that already maps all of the Linux keycodes to appropriate X 
keysyms. The keymap typically used for the old driver is pc105, and I 
suspect that it doesn't have these mappings. They'd be easy to add and 
it's the appropriate place to put them.

Matthew Garrett | mjg59 at

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