Comment 55 for bug 1949394

(In reply to Srihari Vijayaraghavan from comment #52)
> (Whenever Elantech is working, there's always 2 entries for it in dmesg
> without fail as per this dmesg log. And whenever it doesn't work -- just as
> per previous dmesg, obviously there won't be any dmesg entry for it. In
> other words, when it is doesn't work psmouse_extensions() and associates
> don't even get invoked, as per some printk's I peppered around yesterday.
> So it's as if there's no Elantech during psmouse probing. I've since
> abandoned my attempts at studying the problem further, as it was getting too
> difficult for me to comprehend psmouse*.c, elantech.c etc., although I'm not
> so easily discouraged, so I might venture into it again during next weekend
> to understand the path various kernel routines traverse when Elantech is
> detected/working & they fail to traverse when it isn't detected/working.)

When the touchpad doesnt work, it is dumb and deaf and doesn't respond to anything.
Therefore psmouse_probe() - in psmouse-base.c exits immediately.
It looks like it is completly powered down - disconnected from the power source.

If You are interested, read
http://wiki.osdev.org/%228042%22_PS/2_Controller
http://www.win.tue.nl/~aeb/linux/kbd/scancodes-13.html
The PS2 protocol is quite simple.