Re: [PATCH v3 2/3] iio:magnetometer:ak8975: mounting matrix support

[Jonathan Cameron <jic23@kernel.org>]

Backed out patches 2 and 3 for now whilst discussion continues.

On 21/03/16 14:58, Rob Herring wrote:
> On Thu, Mar 17, 2016 at 11:43 AM, Gregor Boirie
> <gregor.boirie@parrot.com> wrote:
>> Expose a rotation matrix to indicate userspace the chip placement with
>> respect to the overall hardware system. This is needed to adjust
>> coordinates sampled from a magnetometer chip when its position deviates
>> from the main hardware system.
>>
>> Final coordinates computation is delegated to userspace since:
>> * computation may involve floating point arithmetics ;
>> * it allows an application to combine adjustments with arbitrary
>>   transformations.
>>
>> This 3 dimentional space rotation matrix is expressed as 3x3 array of
>> strings to support floating point numbers. It may be retrieved from a
>> "in_magn_matrix" sysfs attribute file. It is declared into ak8975 DTS
>> entry as a "matrix" property.
> 
> Why is the sysfs interface specific to ak8975?
> 
> Furthermore, why is it specific to magnetometer? Couldn't
> accelerometers need the same thing? There's a thread discussing a
> similar matrix on android-x86[1].
> 
> 
>> diff --git a/Documentation/devicetree/bindings/iio/magnetometer/ak8975.txt b/Documentation/devicetree/bindings/iio/magnetometer/ak8975.txt
>> index 34a3206..f936f86 100644
>> --- a/Documentation/devicetree/bindings/iio/magnetometer/ak8975.txt
>> +++ b/Documentation/devicetree/bindings/iio/magnetometer/ak8975.txt
>> @@ -9,6 +9,7 @@ Optional properties:
>>
>>    - gpios : should be device tree identifier of the magnetometer DRDY pin
>>    - vdd-supply: an optional regulator that needs to be on to provide VDD
>> +  - matrix: an optional 3x3 mounting rotation matrix
> 
> Perhaps "rotation-matrx" would be a better name in case there's ever
> any other matrix needed.
> 
> Rob
> 
> [1] https://groups.google.com/forum/#!msg/android-x86/LaKhV8cT69o/G1rrVU0_JAAJ
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