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

[Chase Douglas]

On 11/22/2011 03:19 PM, Simon Thum wrote:
> 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.

I think the reason fuzz params haven't been used much is because they
are linux specific. Perhaps we should use them where available, though.

However, it sounds to me like this is an issue of per-axis defuzzing,
whereas what is really needed is distance-based defuzzing. I'm basing
this on Peter's explanation that his circles end up more like squares
with rounded corners.

-- Chase