Message-ID: <3EB23D64.20701@onlinehome.de>
Date: Fri, 02 May 2003 11:41:56 +0200
From: Hans-Georg Thien <1682-600@onlinehome.de>
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To: linux-kernel@vger.kernel.org
Subject: Re: [RFC][PATCH] "Disable Trackpad while typing" on Notebooks withh
 a PS/2 Trackpad
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Ups, it seems that the majordomo has eaten the initial part of the mail...
(Multipart EMail problem?)

Here is the initial posting without the patch

[InitialPart]

Sorry for this long text and my bad english. And please be kind to me -
it is my very first posting to this mailing list ...

I have written a *very small* patch against the linux 2.4.20 kernel and
I want to submit it now.

The short story
---------------
The trackpad on the MacIntosh iBook Notebooks have a feature that
prevents unintended trackpad input while typing on the keyboard. There
are no mouse-moves or mouse-taps for a short period of time after each
keystroke.

I believe that many people with i386 notebooks would like this feature
and I want to give it to the linux community.

First I had the idea of writing a loadable kernel module "trackpad" that
implements that feature and is loadable via

insmod keybd_irq=? mouse_irq=? delay=?

The long story
--------------
My first approach was - because I came from the bad old M$-DOS times -
write something like a "terminate and stay resident program"

       Procedure LoadModule
         Save the currentlly installed handlers for keyboard and mouse.
         Install your own interrupt handlers for keyboard and mouse.
       End

       Procedure UnloadModule
         Stop and remove "reset-timer" if necessary
         Restore the saved interrupt handlers for keyboard and mouse
       End

       Procedure KbdHandler
         Stop or modify "reset-timer" if necessary
         Set global variable block_mouse_events=1
         Start a timer that resets block_mouse_events=0 after ??? mSec
         Call the old keyboard interrupt handler
       End

       Proceure MouseHandler
         if block_mouse_events>0 then
           call ACK(mouse irq) if necessary
           do nothing
         else
           call old mouse interrupt handler
       End


So I bought the book "Linux Device Drivers" written by Alessandro Rubini
& Jonathan Corbert. It is an excellent book about LKM, but I couldn't
find a way  to "save and restore" irq-handlers as in the design
described above.

That's why I requested a little help in the newsgroup at
comp.os.linux.development.system. This ended up with some people who
said "don't mess around with irq-handlers in that way".

While trying to gain a deeper understanding of irq-handling - espically
for mouse and keyboard handlers - I found out that the keyboard and
mouse interrupts are handled *both* in
/usr/src/linux/drivers/char/pc_keyb.c.

Ok, that is only true for PS/2 mice, but the majority of notebooks on
the market have a PS/2 trackpad. On modifiying the pc_keyb.c file there
is no longer a need to save/restore Interrupt handlers or to call them
indirecty via a function pointer. Unfortunatly it has to be compiled in
the kernel and cannot be written as a LKM module.

But anyway - I sad down and got a working solution very quickly! I'm
very glad with it! I needed not more than 45 minutes to get this
working! Works in textmode (gpm) and under X11 as expected!


Testing
-------
I have tested my patch only on my own notebook (Compaq M300). It would
help a lot if there are some volunteers...


Future Plans
------------
[x] make the "disable trackpad time" configurable via the /proc
filesystem. Do you think that /proc/sys/kernel/trackpad is a good place
for it? There are other files under the /proc/sys/kernel directory that
fall in the category "keyboard handling", e.g. ctrl-alt-del or sysrq.

[x] make a /proc entry to allow "disable trackpad" and "enable
trackpad". That would allow to turn the builtin trackpad off when an
external mouse is pluged in, and to re-enable it when an external mouse
is unplugged again.

[/InitialPart]


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