linux-kernel - Re: [PATCH] CHROMIUM: Input: synaptics - filter out the events with low z values

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Message-ID: <20120222110459.GA28126@polaris.bitmath.org>
Date:	Wed, 22 Feb 2012 12:04:59 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Chung-yih Wang <cywang@...omium.org>,
	Alessandro Rubini <rubini@...vis.unipv.it>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] CHROMIUM: Input: synaptics - filter out the events with
 low z values

Hi Daniel,

> > So if num_fingers == 2 and only one of a and b returns
> > finger_touched() == true, we fall back to zero fingers?
> 
> Actually, yes.   In this case, we will have 2 x's and 2 y's, but not
> know which belong to a good finger and which belong to a too light
> finger....  sigh... synaptics... sigh...

I see the problem. However, ignoring it will just move the problem
forward to another bug report, will it not?  Hysteresis is a slam dunk
here.  In addition, since the low-pressure state is bound to be
transitional (soon to be followed by a real num_fingers==1 package),
simply skipping such packages might be a better option.

> > Why not introduce hysteresis for all fingers here? There is an example
> > implementation in bcm5974.c in the same directory.
> 
> Good idea, can it be in a different, follow-up patch?

Why should it be?

Thanks,
Henrik
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