linux-kernel - Caps lock XOR on multiple keyboards?

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Date:	3 Dec 2012 16:19:11 -0500
From:	"George Spelvin" <linux@...izon.com>
To:	alan@...ux.intel.com, chris@...-brannons.com,
	gregkh@...uxfoundation.org, jslaby@...e.cz
Cc:	linux@...izon.com, linux-kernel@...r.kernel.org
Subject: Caps lock XOR on multiple keyboards?

(Not sure who owns this; Cc: to the last few people to touch
drivers/tty/vt/keyboard.c.)

I happen to have both a PS/2 and USB keyboard plugged, in, but was
noticing that the caps lock key seemed inverted.  When the LED was off,
I got all caps (unless I used shift), while when it was on I got normal
lower-case letters.

This quite confused me, until I looked over and saw that someone had
hit caps lock on the PS/2.

Experimenting, it seems that each keyboard has its own caps lock LED
state, and the XOR of the two controls the case of the letters.

The corresponding shift keys have a shared logical state which depends
on who last had a transition.  Holding down left-shift on one can be
cancelled by pressing and releasing left-shift on the other.  (But
left & right shift are tracked separately.)

It would make more sense if each keyboard's caps lock LED controlled
the effect on its keys.  Either give each keyboard a completely separate
caps lock state, or toggle both LEDs when either caps lock is pressed.

Perhaps the answer is "It's too much work to fix; stop doing something
so stupid", but I thought I'd at least mention it.

(Er... it appears that my XOR description was incomplete.  I now have
the keyboard system in a state where *one* caps lock LED has to be on
to get normal lower-case letters.  I was playing with down1/down2/up1/up2
combinations, but I'm not quite sure what happened...)
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