linux-kernel - Re: [PATCH 37/51] Input: atmel_mxt_ts - Implement vector/orientation support

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Message-ID: <520CFF6C.7020302@itdev.co.uk>
Date:	Thu, 15 Aug 2013 17:18:52 +0100
From:	Nick Dyer <nick.dyer@...ev.co.uk>
To:	rydberg@...omail.se
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	Alan Bowens <Alan.Bowens@...el.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peter Meerwald <pmeerw@...erw.net>,
	Benson Leung <bleung@...omium.org>,
	Olof Johansson <olofj@...omium.org>
Subject: Re: [PATCH 37/51] Input: atmel_mxt_ts - Implement vector/orientation
 support

rydberg@...omail.se wrote:
> On Thu, Jun 27, 2013 at 01:49:12PM +0100, Nick Dyer wrote:
>> The atmel touch messages contain orientation information as a byte in a packed
>> format which can be passed straight on to Android if the input device
>> configuration is correct, see
>> http://source.android.com/tech/input/touch-devices.html#touchorientationcalibration

Except they've changed the URL, should be:
https://source.android.com/devices/tech/input/touch-devices.html#touchorientationcalibration

The Atmel format is two 4-bit signed values packed into 1 byte, you use
inverse tan to work out the angle, and pythagoras theorem to work out the
magnitude of the vector (giving a confidence level)

>> This requires vector reports to be enabled in maXTouch config (zero DISVECT
>> bit in T9 CTRL field)
>>
>> Android converts the format in frameworks/base/services/input/Input.cpp,
>> search for ORIENTATION_CALIBRATION_VECTOR.
> 
> How does this compare to the input mt documentation?

http://lxr.free-electrons.com/source/Documentation/input/multi-touch-protocol.txt#L263

So yes, we don't meet the documented format. Options:
1. Leave out this patch entirely and support out of tree
2. Update multi-touch-protocol.txt to include the Atmel format
3. Convert in driver to match documented protocol. Presumably via a LUT of
the 256 possible values. Although this loses the confidence level that is
implied.
4. Getting the firmware changed is not a valid option I'm afraid (too many
devices already out there).

Which do you prefer (I suspect 3) ?
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