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

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Message-Id: <201005271612.21794.dmitry.torokhov@gmail.com>
Date:	Thu, 27 May 2010 16:12:20 -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 Thursday, May 27, 2010 03:59:37 pm Ping Cheng wrote:
> On Thu, May 27, 2010 at 12:03 AM, Dmitry Torokhov
> 
> <dmitry.torokhov@...il.com> wrote:
> > 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.
> 
> tbh, I can not say that I will need it in my X driver for sure. But I
> vote for it to be merged.

Well, at this point I am in "no users - no functionality" mode, so I will
only count votes of users :P

-- 
Dmitry
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