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

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Message-ID: <20120224092351.GA2203@polaris.bitmath.org>
Date:	Fri, 24 Feb 2012 10:23:51 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Daniel Kurtz <djkurtz@...omium.org>,
	Chung-yih Wang <cywang@...omium.org>,
	Alessandro Rubini <rubini@...vis.unipv.it>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] CHROMIUM: Input: synaptics - filter out the events with
 low z values

On Fri, Feb 24, 2012 at 01:16:02AM -0800, Dmitry Torokhov wrote:
> On Fri, Feb 24, 2012 at 01:14:52AM -0800, Dmitry Torokhov wrote:
> > On Fri, Feb 24, 2012 at 10:08:35AM +0100, Henrik Rydberg wrote:
> > > > > The most striking effect is the ability to better retain a
> > > > > drag. Although the statement was made in light of possible
> > > > > (1-strong,1-weak) packets, it should help in the 2-weak case too.
> > > > 
> > > > The bigger question is why is this needed in kernel. The original
> > > > hysteresis with BTN_TOUCH was done for sole benefit of mousedev so that
> > > > we could allow somewhat better transition from standard PS/2 mode into
> > > > native Synaptics mode with absolute coordinates at time when barely
> > > > anyone had Synaptics X driver installed. This was, what, 10 years ago?
> > > 
> > > The semi-mt behavior is obviously a special case, where userspace
> > > relies on the reported number of fingers to transition between one
> > > touch and two touches. There is no pressure information sent to
> > > userspace in this case, so the situation is in fact quite similar to
> > > the ancient mousedev situation.
> > 
> > We still report ABS_PRESSURE but maybe we should report ABS_MT_PRESSURE
> > as well?
> 
> BTW, the reason I do not like this in kernel is because it dos not allow
> users control touchpad sensitivity.

...which is perfectly reasonable, I agree. OTOH, the semi-mt devices
tend to report close-to-bogus information for anything related to
individual touches. Pressure is sadly no different, as Daniel pointed
out. I don't know what is the lesser evil here.

Henrik
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