Possible regression with "Add hysteresis-based noise reduction" in synaptics driver

[Simon Thum]

Hi Peter(s),

the story behind the default noise cancellation is that I chose what
worked well on my system (25) and figured out a reasonable fraction of
the diagonal that approximately gave me that number (0.5%; see
set_default_parameters).

"My system" refers to an old HW I no longer have in active use, and
pretty much every pad I ran across had better noise characteristics. So,
I'm in favour of lowering the default value to something more modern HW
does well with. Maybe 0.25 %?

The reason for defining it as a fraction of the diagonal is to be more
HW invariant than with a fixed value, but it's also something more or
less made up from thin air.

Before I forget, it's possible (in theory) for the kernel to supply
"fuzz" values, but I haven't seen that in practical use. Those could
make it into your property, but I suspect that is what happens.

Cheers,

Simon

On 11/22/2011 12:22 AM, Peter Clifton wrote:
> Hi guys,
> 
> Recently I've been having some difficulties with my touchpad. I do a lot
> of electronics design work, and this often requires making small precise
> movements with the pointer.
> 
> Just recently though, this has been much harder - I've found myself
> getting frustrated with the CAD package, and I'd started to think my
> touchpad was broken... (so I started investigating). It definitely
> seemed that I was unable to persuade the touchpad to produce smooth
> motions of a small number of pixels.
> 
> I tried drawing some circles using the touchpad, and they would come out
> with flattened edges.
> 
> I found that by setting the "Synaptics Noise Cancellation" property
> using "xinput", I was able to restore "correct" behaviour. I guess the
> default setting is picking up a default which is not well suited to my
> laptop (HP 6730b) hardware.
> 
> Any pointers (no pun intended) you can suggest to investigate why the
> default is inappropriate on my system would be great. I'll try to follow
> up with what the default _is_ on this box when I next reboot. For now,
> I've been fixing the issue with:
> 
> xinput set-int-prop 11 313 32 10 10
> 
> So I don't have the old setting readily to hand. (I did attach the
> current settings. I've only modified the noise cancellation one).
> 
> Thanks
>