linux-kernel - Re: [PATCH 0/4] Alternative approach to MT_TOOL

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Date:	Wed, 15 Dec 2010 20:36:08 +0100
From:	Henrik Rydberg <rydberg@...math.org>
To:	Chase Douglas <chase.douglas@...onical.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Chris Bagwell <chris@...bagwell.com>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	linux-input <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] Alternative approach to MT_TOOL_ENVELOPE

>>> I think that presence of pen/touch can be detected by having

>>> BTN_TOOL_PEN and BTN_TOOL_FINGER. However in this case the tool is
>>> finger, so I do not think we should introduce BTN_TOOL_ENVELOPE. Maybe
>>> this is another case where we should employ the proposed device flags?
>>
>> Yes. Having something like INPUT_QUIRK_SEMI_MT might be enough, and we could
>> drop the whole MT_TOOL_ENVELOPE circus. Chase, Peter, Chris, would you be
>> comfortable with such a solution?
> 
> That sounds like a good solution to me. I believe it would resolve all
> the issues I had.


Sounds good.


> As I attempted to write up more documentation, I thought of the
> following. What do you think?
> 
> With regards to partial MT devices, if the device provides a single
> valued property, such as pressure and tool type for synaptics, it may
> only be provided through the traditional property semantics, i.e.
> ABS_PRESSURE and BTN_TOOL_*. If the device provides multiple values for
> a property, then ABS_MT_* types may be used as well to provide up to two
> values, though the client should understand there's no direct
> correlation between the slot's coordinates and the property. I could see
> this being used to provide info on multiple tool types or a high and low
> pressure.
> 
> Enforcing the above behaviour provides even more information about the
> capabilities of the device based solely on the evdev codes published.


Looks good, but I do not think we need to formalize all possibilities here, only
the usage of MT data for bounding rectangle and ST data for finger count.
Referring to the patch just sent: whenever INPUT_PROP_SEMI_MT is true, this
behavior is expected. In the event of new odd hardware, the combination of a new
property quirk and a documented recipe should do the trick.

Thanks,
Henrik
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