[Trusty/Utopic][PATCH 2/2] HID: multitouch: Add support for button type usage

[Seth Forshee]

On Thu, May 28, 2015 at 05:00:48PM +0800, Adam Lee wrote:
> From: Seth Forshee <seth.forshee at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1456881
> 
> According to [1], Windows Precision Touchpad devices must supply
> a button type usage in the device capabilities feature report. A
> value of 0 indicates that the device contains a depressible
> button (i.e. it's a click-pad) whereas a value of 1 indicates
> a non-depressible button. Add support for this usage and set
> INPUT_PROP_BUTTONPAD on the touchpad input device whenever a
> depressible button is present.
> 
> [1] https://msdn.microsoft.com/en-us/library/windows/hardware/dn467314(v=vs.85).aspx
> 
> Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
> Reviewed-by: Benjamin Tissoires <benjamin.tissoires at redhat.com>
> Signed-off-by: Jiri Kosina <jkosina at suse.cz>
> (cherry picked from commit 2c6e0277e1eab3df5db81c59e408b7b1c14b1b72)
> Signed-off-by: Adam Lee <adam.lee at canonical.com>

>From the bug:

> We found under some extreme system usage that comment #2 can fix the
> problem.
> 
> Run some application/operation (e.g: Play youtube on background, launch
> libreoffice for awhile (about 5-10min) or insert USB to copy some files
> : The touchpad cursor were no function after some operation, sometime it
> scrolling automatically or keep send press signal.
> 
> Without the patch of comment #2, when the issue occurred we also check
> the touchpad event on ttyl1 by "evtest", we can found the event keeping
> output without move cursor/click touchpad.

This doesn't make any sense to me. All of the detection done by this
patch happens when the device is probed, and once INPUT_PROP_BUTTONPAD
is set it shouldn't get cleared later due to heavy load. The device is
defined in the ACPI tables, so it's not going to be vanishing then
reappearing to be reprobed.

So I'm skeptical that this patch really fixes the problem. Not that I
think it will do any harm, but I can't understand how it would possibly
help.

Seth