linux-kernel - Re: [PATCH 0/2] input: mt: Add EVIOC mechanism for MT slots

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Date:	Thu, 27 May 2010 00:03:10 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Ping Cheng <pinglinux@...il.com>
Cc:	Henrik Rydberg <rydberg@...omail.se>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Stephane Chatty <chatty@...c.fr>,
	Rafi Rubin <rafi@...s.upenn.edu>,
	Michael Poole <mdpoole@...ilus.org>
Subject: Re: [PATCH 0/2] input: mt: Add EVIOC mechanism for MT slots

On Wed, May 26, 2010 at 08:59:35AM -0700, Ping Cheng wrote:
> On Tue, May 25, 2010 at 1:23 PM, Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> > On Tue, May 25, 2010 at 09:52:29PM +0200, Henrik Rydberg wrote:
> >> Dmitry Torokhov wrote:
> >> > Hi Henrik,
> >> >
> >> > On Tue, May 25, 2010 at 01:52:57PM +0200, Henrik Rydberg wrote:
> >> >> These patches are in response to the discussion about input state
> >> >> retrieval.
> >> >>
> >> >> The current EVIOCGABS method does not work with MT slots.  These
> >> >> patches provides a mechanism where a slot is first selected via a call
> >> >> to EVIOCSABS, after which the corresponding MT events can be extracted
> >> >> with calls to EVIOCGABS.
> >> >>
> >> >> The symmetric operation, to set the MT state via EVIOCSABS, seems to
> >> >> violate input data integrity, and is therefore not implemented.
> >> >>
> >> >
> >> > This looks sane, however the question remains - is there any users for
> >> > this data? Like I mentioned, I can see the need to fetch state of
> >> > switches and ranges of absolute axis, and even non-multitouch ABS values
> >> > (due to the fact that some input devices, like sliders, may stay in a
> >> > certain position for long periods of time), but I expect multitouch data
> >> > to be "refreshed" very quickly.
> >> >
> >> > Thanks.
> >> >
> >>
> >> There were some voices addressing this issue, and the patches are here,
> >> available for whomever to pick up. Drop them if you wish, I will not send them anew.
> >>
> >
> > I'll save them in my queue but will hold off applying until I hear
> > userspace folks requesting such functionality.
> 
> Hi Dmitry,
> 
> You do have a valid point - the (x,y) from a touch object would most
> likely change all the time. Even if the object itself is in a steady
> state on the digitizer, i.e., without any intentional movement, the
> electronic noise would most likely lead to some (x,y) changes. So, the
> chance that we need to retrieve (x,y) is rare.
> 
> However, it is possibe that when X driver starts, an object was
> already on the digitizer. And the digitizer is of such a high quality
> :), it filtered all the noises so we can not locate the touch without
> a EVIOCGABS call.
> 
> Plus, from a pure coding/development point of view, it is not a bad
> practice to provide the equivalent features for _MT_ support as we did
> for the existing input devices. At least, it doesn't hurt to make the
> support consistent across devices/tools (considering touch as a new
> input device/tool).

Ping,

I did not say that there was a problem with the patch, I agree with it.
However if no one using this - why should we bother? Will _you_ utilize
this functionality in Wacom X driver? If so let me know and I will merge
it.

-- 
Dmitry
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