I have a problem with ELAN1200 touchpad, the touchpad is installed in some ASUS ultrabooks: UX310, UX410, UX330, UX360, may be others. In general it works as a hid-i2c device but has the idiosyncrasies. It reports several hid usages with the code 0x900c5 and one of them is height/weight of a contact decoded in 4 bytes. But it's actually isn't a problem, I can extract it in the raw event. It also some times reports fake events for the fifth contact, it's not a big problem either.

The actual problem is that when two contacts are close enough, let's say a diagonal between contact coordiantes is less than 400 units in touchpad's coordinates, touchpad automaticaly fires release events for the contacts and starts report them as one contact with the coordianates something around the means of the previous two ones. This behaviour causes random right-button two-finger taps during two finger scrolling.

I'm trying to tackle the problem in my custom driver
https://github.com/mishurov/linux_elan1200_touchpad

I have a shallow experience with kernel drivers and I need help. These are decoded reports I've printed from a userspace driver to show the occasions when I want to suppress the release events.

This is when the touchpad starts to report two fingers as one:

id 1 -        994  -        441  - 64 -  5 -  4 - 1
id 0 x 1406        y  287        c 64 w  4 h  4 t 1
id 1 -        994  -        441  - 64 -  5 -  4 - 1
id 0 x 1406        y  287        c 64 w  4 h  4 t 1
id 1 -        994  -        441  -  0 -  5 -  4 - 0
id 0 x 1406        y  287        c  0 w  4 h  4 t 0
id 1 -       1146  -        390  - 64 -  6 -  5 - 1
id 1 -       1146  -        390  - 64 -  6 -  5 - 1
id 1 -       1146  -        390  - 64 -  6 -  5 - 1
id 1 -       1146  -        390  - 64 -  6 -  5 - 1

id: id of a contact
c: confidence (encoded with a clickpad button state)
x, y: coords (x: 0 - 3200, y: 0 - 2198)
w, h: width, height (both: 0 - 15, unscaled according to the h/w ratio of a touchpad)
t: 1 for touch, 0 for release


This is the report when two fingers are being reported as one and then the distance between them becomes big enough and the touchpad starts to report them as two contacts.

id 0 x 1359        y  275        c 64 w  7 h  5 t 1
id 0 x 1360        y  274        c 64 w  7 h  5 t 1
id 0 x 1360        y  274        c 64 w  7 h  5 t 1
id 0 x 1360        y  274        c 64 w  7 h  5 t 1
id 0 x 1360        y  274        c  0 w  7 h  5 t 0
id 0 x 1200        y  411        c 64 w  5 h  5 t 1
id 1 -       1556  -        108  - 64 -  4 -  4 - 1
id 0 x 1200        y  411        c 64 w  5 h  5 t 1
id 1 -       1556  -        108  - 64 -  4 -  4 - 1
id 0 x 1200        y  411        c 64 w  5 h  5 t 1
id 1 -       1556  -        108  - 64 -  4 -  4 - 1
id 0 x 1200        y  411        c 64 w  5 h  5 t 1
id 1 -       1556  -        108  - 64 -  4 -  4 - 1


These transitions happen without actual releases of contacts but touchpad reports the releases and I want to supress them. Because it happens quite often during two-finger scrolling. A Xorg driver eventually reports either a random two-finger right-tap or a tap-and-drag gesture because of those artificial release events.

My problem is that at the moment when the touchpad reports a release I can't say with the probability of 1 whether it's an actual release or it starts splicing the contacts, I can check it only on the next touch events. But if it was an actual release then there would be no further reports and if I just suppress the release event it will be the "sticky fingers" problem.

Is there a some kind of a delayed queye in kernel to report an event one step later? I tried to use timers. Or may be there's some other solution. Or may be it should be handlend in a userspace driver.