apply filters to ABS_MT_TOOL_X/Y too

[merge]

I think we can expect that not only ABS_MT_POSITION_X/Y must be filtered, but if available by the hardware's driver, also ABS_MT_TOOL_X/Y.

By the way, see https://blackfin.uclinux.org/lib/exe/fetch.php?media=presentations:linux_multi-touch_mt_protocol.odp for a nice presentation.

[merge]

should this involve, showing the position of ABS_MT_TOOL_X/Y in ts_test_mt somehow too?

[merge]

we could get a little creative here with out test tools. This topic is now scheduled for 1.4 and any help or hardware suggestion is welcome. some theory from kernel.org :

• ABS_MT_TOOL_X

The surface X coordinate of the center of the approaching tool. Omit if
the device cannot distinguish between the intended touch point and the
tool itself.

• ABS_MT_TOOL_Y

The surface Y coordinate of the center of the approaching tool. Omit if the
device cannot distinguish between the intended touch point and the tool
itself.

The four position values can be used to separate the position of the touch
from the position of the tool. If both positions are present, the major
tool axis points towards the touch point [1]. Otherwise, the tool axes are
aligned with the touch axes.

[1] Also, the difference (TOOL_X - POSITION_X) can be used to model tilt.

AD's mentioned protocol presentation slides are attached:
linux_multi-touch_mt_protocol.pdf

[merge]

as of 1.13 we have the TSLIB_MT_VALID bit defined as 1 for the valid variable. It gets set if there's any new data anywhere in ts_sample_mt. TSLIB_MT_VALID_TOOL is reserved and gets set additionally in case there's data in tool_x or tool_y.

so if (valid & TSLIB_MT_VALID_TOOL) we allocate new buffers and operate everything on those values too.