[PATCH synaptics] Revert "Don't store fake events in the motion history"

[Daniel Stone]

Hi,

On 20 February 2012 00:20, Peter Hutterer <peter.hutterer at who-t.net> wrote:
> This commit introduced a regression. On some touchpads, the pointer keeps
> moving in the last direction when the finger movement stops but the finger
> is left on the touchpad.
>
> Cause appears to be get_delta() which calculates the deltas based on the
> motion history but has no control flow for the lack of fake motion events
> in the history after this commit. Thus, under some conditions, the delta is
> always non-zero as the history does not change.
>
> Reproducer attached to bug
> https://bugs.freedesktop.org/show_bug.cgi?id=45278#c11
>
> X.Org Bug 45278 <http://bugs.freedesktop.org/show_bug.cgi?id=45278>
>
> This reverts commit c8b098214b44cf0585d78c460401ea7d143769f3.
>
> Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>

Acked-by: Daniel Stone <daniel at fooishbar.org>

Yes, this was both designed for and only works on, terrible hardware.
It was meant to give more accurate motion by actually calculating the
new events based on real history, rather than calculations based on
calculations based on real history.  Unfortunately, this gets
subverted by hardware which is too accurate.  Synaptics PS/2 pads
can/could usually be relied on to give enough jitter once your finger
had stopped that we'd filter out the motion and stop it.  However,
some newer Synaptics pads as well as pads from other manufacturers
tend to not deliver any jittery events once your finger has stopped,
which is bad news since evdev filters out duplicate events.

I'm not really sure how to fix this (a property indicating a lame
touchpad with a whitelist? making sure we don't generate too many fake
motion events? probably both ...) and don't have a whole whack of time
or devices to test with now, so the revert is OK by me.  Hopefully we
can revisit this later, because it does subjectively produce 'better'
events.  Except when it catastrophically fails.

Cheers,
Daniel