Bug 15755 - intermittent spurious button 2 events
intermittent spurious button 2 events
Product: Drivers
Classification: Unclassified
Component: Input Devices
All Linux
: P1 high
Assigned To: drivers_input-devices
Depends on:
Blocks: 14885
  Show dependency treegraph
Reported: 2010-04-11 07:56 UTC by Clemens Buchacher
Modified: 2010-12-08 08:30 UTC (History)
5 users (show)

See Also:
Kernel Version: 2.6.33
Tree: Mainline
Regression: Yes


Description Clemens Buchacher 2010-04-11 07:56:33 UTC
I reported this bug previously to Xorg https://bugs.freedesktop.org/show_bug.cgi?id=26079 , where it was confirmed by Mathieu Marquer.

Steps to reproduce.

1. $ xev | grep -v 'button [^1]'
2. repeatedly press left touchpad button until xev reports "button 2"

It usually takes 10-20 repetitions of the above process for this to happen.
If it does not happen, doing something else like switching windows usually
helps trigger the problem again.

Sometimes both button events are generated, sometimes only button 2.

I can _not_ reproduce the problem with a USB mouse.

I bisected the bug to commit 315eb996 (Input: psmouse - rework
setting of BTN_MIDDLE capability), which is part of the 2.6.33 release. Reverting that commit from the current tip of the nouveau kernel tree v2.6.34-rc2-760-g2c9a8fe fixes the issue.


Xorg version 7.5+3 (Debian package)
Xorg synaptics driver version 1.2.1-1 (Debian package)

* scripts/ver_linux output

Linux darc 2.6.34-rc2-00760-g2c9a8fe #9 SMP PREEMPT Sat Apr 10 23:42:12 CEST 2010 x86_64 GNU/Linux
Gnu C                  4.3.4
Gnu make               3.81
binutils               2.20
util-linux             2.16.2
mount                  support
module-init-tools      3.11
e2fsprogs              1.41.9
Linux C Library        2.10.2
Dynamic linker (ldd)   2.10.2
Procps                 3.2.8
Net-tools              1.60
Console-tools          0.2.3
Sh-utils               7.4
wireless-tools         30
Modules Loaded         bridge stp llc rfcomm ipv6 kvm_intel cpufreq_stats cpufreq_conservative cpufreq_powersave cpufreq_userspace cpufreq_ondemand binfmt_misc uinput bpa10x hci_uart hci_vhci btsdio microcode bcm203x usbserial ohci_hcd cifs acpi_cpufreq freq_table container sbs kvm msr cpuid sbshc display lcd led_class sco hidp bnep l2cap gspca_zc3xx gspca_main snd_pcm_oss snd_mixer_oss fuse nouveau ttm drm_kms_helper drm fan video processor iwlagn pcmcia thermal thermal_sys ac i2c_algo_bit iwlcore cfbcopyarea cfbimgblt btusb mac80211 bluetooth yenta_socket rtc_cmos rsrc_nonstatic output i2c_i801 cfbfillrect battery button i2c_core sg cfg80211 rfkill uvcvideo evdev joydev
Comment 1 Dmitry Torokhov 2010-04-12 16:44:17 UTC
The commit you referenced did not alter the way input events are generated so I am not sure what is going on. What kind of hardware is it? Also, is it reproducible with evtest utility on console?
Comment 2 Rafael J. Wysocki 2010-04-12 21:38:17 UTC
Handled-By : Dmitry Torokhov <dmitry.torokhov@gmail.com>
Comment 3 Clemens Buchacher 2010-04-12 22:32:47 UTC
About the device, dmesg says:

Synaptics Touchpad, model: 1, fw: 6.2, id: 0x25a0b1, caps: 0xa04713/0x200000
input: SynPS/2 Synaptics TouchPad as /devices/platform/i8042/serio4/input/input2

I should have mentioned this before, but the touchpad does _not_ have a
physical middle mouse button. Pressing both mouse buttons simultaneously acts
as a middle mouse button by default. This behavior can be deactivated by
setting synclient EmulateMidButtonTime=0. This does not disable the button 2
events generated by the bug, however.

I could not reproduce the bug with evtest. It is hard to work with,
because it does not flush its output very often, produces a lot of output, and
I'm not sure what I am looking for.

As for the cause of the bug, maybe with the change the device is advertised as
a 3-button mouse so that previously ignored/suppressed events are now coming
through. But that is only a wild guess.
Comment 4 Dmitry Torokhov 2010-04-12 23:03:42 UTC
It used to advertising itself as 3-button mouse, but not anymore. What does /proc/bus/input/devices show on your box?

I am not sure why evtest would not flush on your machine, it seems to be doing this on mine. I would look for:

 Event: time 1271113350.785485, type 1 (Key), code 273 (RightBtn), value 1

instead of

 Event: time 1271113376.560063, type 1 (Key), code 272 (LeftBtn), value 1

To confirm that the kernel is generating wrong events.

What does lsof /dev/input/event* show on your box BTW?
Comment 5 Clemens Buchacher 2010-04-13 09:27:14 UTC
Ok. This is most likely caused by the multifinger-click feature.  The
synaptics driver generates a button 2 event if it detects three fingers
pressed at the same time. This feature is disabled by default if the
touchpad has a middle button, which is why it did not happen before. A
simple synclient ClickFinger3=1 deactivates it. 

Apparently, the multifinger detection is not very accurate, since I
triggered it accidentally all the time. I will ask in the Xorg bug report to
disable it by default.

Since this has nothing to do with the kernel any more, I think we can close
this bug report. Thank you for your help.


Since I already had it prepared, here is the data you requested.

On Mon, Apr 12, 2010 at 11:03:55PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:

> It used to advertising itself as 3-button mouse, but not anymore. What does
> /proc/bus/input/devices show on your box?

I: Bus=0011 Vendor=0002 Product=0007 Version=25b1
N: Name="SynPS/2 Synaptics TouchPad"
P: Phys=isa0060/serio4/input0
S: Sysfs=/devices/platform/i8042/serio4/input/input2
U: Uniq=
H: Handlers=mouse0 event2 
B: EV=b
B: KEY=6420 30000 0 0 0 0
B: ABS=11000003

With the patch reverted the only difference is this line.

B: KEY=6420 70000 0 0 0 0

> What does lsof /dev/input/event* show on your box BTW?

acpid      2060 root    3r   CHR  13,64      0t0 1686 /dev/input/event0
acpid      2060 root    4r   CHR  13,68      0t0 1794 /dev/input/event4
acpid      2060 root    5r   CHR  13,69      0t0 1849 /dev/input/event5
acpid      2060 root    6r   CHR  13,70      0t0 1801 /dev/input/event6
acpid      2060 root    7r   CHR  13,71      0t0 1807 /dev/input/event7
acpid      2060 root    8r   CHR  13,72      0t0 1921 /dev/input/event8
acpid      2060 root    9r   CHR  13,73      0t0 3054 /dev/input/event9
hald-addo  2519 root    4r   CHR  13,73      0t0 3054 /dev/input/event9
hald-addo  2519 root    5w   CHR  13,64      0t0 1686 /dev/input/event0
hald-addo  2519 root    6r   CHR  13,65      0t0 1674 /dev/input/event1
hald-addo  2519 root    7r   CHR  13,70      0t0 1801 /dev/input/event6
hald-addo  2519 root    8r   CHR  13,69      0t0 1849 /dev/input/event5
hald-addo  2519 root    9r   CHR  13,72      0t0 1921 /dev/input/event8
hald-addo  2519 root   10r   CHR  13,71      0t0 1807 /dev/input/event7
hald-addo  2519 root   11r   CHR  13,68      0t0 1794 /dev/input/event4
Xorg      13632 root   12u   CHR  13,71      0t0 1807 /dev/input/event7
Xorg      13632 root   13u   CHR  13,72      0t0 1921 /dev/input/event8
Xorg      13632 root   14u   CHR  13,69      0t0 1849 /dev/input/event5
Xorg      13632 root   15u   CHR  13,70      0t0 1801 /dev/input/event6
Xorg      13632 root   16u   CHR  13,65      0t0 1674 /dev/input/event1
Xorg      13632 root   17u   CHR  13,64      0t0 1686 /dev/input/event0
Xorg      13632 root   18u   CHR  13,66      0t0 1702 /dev/input/event2
Xorg      13632 root   19u   CHR  13,73      0t0 3054 /dev/input/event9
Comment 6 Florian Mickler 2010-12-08 08:30:02 UTC
Ok, closing.

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