odd PS/2 keyboard fail

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

I've got a machine (a Gigabyte GA-7VTXE board with an Athlon 2600+ in
it) which has for a long time been running, more or less happily, under
my 1.4T (a slightly hacked-up 1.4T, but I don't think I've touched the
relevant bits).

Today I tried 4.0.1 on this hardware.  To my surprise, the keyboard in
the PS/2 keyboard port simply does not work past the point of the
bootloader handing control over to the kernel, though it works fine up
to that point.  (The symptom is that keystrokes are ignored; for all I
can tell from the response I get, I might as well not be typing at
all.)  It's clearly not the hardware, both because it works before that
and because 1.4T has no problems.  And it's not just a lack of PS/2
keyboard support in the kernel; that same boot drive. including the
kernel, works just fine, including the same PS/2 keyboard, on an IBM P4
board.  The Gigabyte board also works fine if I put the keyboard behind
a PS/2-to-USB adapter in one of the USB ports, though not if I plug it
in only after boot.

Surely this is not expected behaviour.  Does anyone but me care?  If
so, how can I best help debug it?  Just post dmesg output, or is there
something I should make sure is turned on first?

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