Bug 39226

Summary:	syndaemon sometimes fails to disable the touchpad while typing
Product:	xorg	Reporter:	Oliver Joos <oliver.joos>
Component:	Input/synaptics	Assignee:	Peter Hutterer <peter.hutterer>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	7.5 (2009.10)
Hardware:	All
OS:	Linux (All)
Whiteboard:
i915 platform:		i915 features:

Description Oliver Joos 2011-07-14 08:42:56 UTC

I use Ubuntu 10.04.2 LTS with xorg 1:7.5+5ubuntu1 and xserver-xorg-input-synaptics 1.2.2-1ubuntu4

To reproduce start a terminal and execute
1. killall syndaemon
2. syndaemon -i 4.0 -k
3. then press keys and move pointer with touchpad at once

Two things go wrong:
* syndaemon writes "Disable" and "Enable" to stdout, but
  enables not always 4.0 secs after the last keypress.
* quite often the pointer still moves although syndaemon
  says it is disabled.

Details have been well explained by Stanley Sokolow as comment #20 on http://launchpad.net/bugs/27541 which is one of many duplicates of http://launchpad.net/bugs/240738. The low default timeout of 0.5 secs in Ubuntu makes it even worse and seems a workaround for http://launchpad.net/bugs/801763

Due to recent diversity of touchpad hardware this bug gains publicity. I found that Macbooks, newer Samsung laptops and Asus EeePCs are among the affected systems. See my findings with Elantech touchpads in comment #27 of http://launchpad.net/bugs/240738

Comment 1 Mike 2011-07-15 05:03:56 UTC

Not to toot my own horn here, but I contacted Peter Osterlund, the author of the syndaemon man page, and his response suggests that it isn't just a simple change of the default timing as suggested in comment 20 of the aforementioned bug:
https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-input-synaptics/+bug/240738/comments/5

Comment 2 Peter Hutterer 2011-07-27 18:08:05 UTC

Did you try using the record extension instead of polling?

syndaemon -R -i 4.0 -k

Comment 3 Tim 2011-08-13 06:19:52 UTC

Using the undocumented option "-m 20" on syndaemon, as mentioned in LP #240738, made the situation a lot better for me. At least most keypresses are catched now.

Comment 4 Tim 2011-08-13 06:38:48 UTC

(In reply to comment #2)
> Did you try using the record extension instead of polling?
> 
> syndaemon -R -i 4.0 -k

If you press a key real quick it still misses it sometimes (apart from the fact that not being able to click for 4 seconds after the last letter you typed is very annoying by itself).

I experimented with this undocumented switch -m to change the polling interval and running "syndaemon -R -i 0.5 -k -m 20", which changes the default polling interval of 200ms to 20ms, results in no more noticeable key presses being missed.

Comment 5 Peter Hutterer 2011-08-14 15:22:36 UTC

If you use -R, the -m argument is ignored.

Comment 6 Peter Hutterer 2012-03-13 21:27:39 UTC

(In reply to comment #3)
> Using the undocumented option "-m 20" on syndaemon,

commit 72d5b4886927aee5fbc871b5c3d0300be92d8ecc
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Thu Jul 28 10:43:38 2011 +1000

    man: document syndaemon -m switch

Comment 7 Peter Hutterer 2012-03-13 21:38:46 UTC

Closing as fixed as per comment #4. Since -m 20 is ignored if -R is given, I can assume that -R is enough to fix the issue. GNOME also uses the -R flag nowadays, see https://bugzilla.gnome.org/show_bug.cgi?id=639623

Long story short, any polling suffers from race condition, so this cannot be fixed in normal mode.

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