Re: [PATCH v2 4/5] iio:magnetometer:ak8975: mounting matrix support

[Jonathan Cameron <jic23@kernel.org>]

On 14/03/16 17:19, Gregor Boirie wrote:
> On 03/09/2016 09:46 PM, Jonathan Cameron wrote:
> 
> [snip...]
>> Definitely needs ABI docs in Documentation/ABI/testing/sysfs-bus-iio
>> as well. We need the reference directions to be well specified as
>> well - how do we define the main hardware orientation?  on yours presumably
>> the usual approach of using the screen is irrelevant so that definition
>> could be a little 'interesting' to write down?
>>> The standard orientation for us is defined with respect to the drone's head
>>> and the propellers plane, which does not suit the nominal use cases indeed...
>>> Although it really deserves some more detailed documentation, I wonder if the
>>> question is relevant.
>>> Given that the DTS is board specific (correct me if I'm wrong), why not
>>> consider the reference orientation as board specific as well (and make the
>>> whole thing implicit) ?
>> I think that is fine for your sort of usecase - though might be nice to keep
>> a bit of documentation somewhere (perhaps as comments in the DTS), or perhaps
>> more centrally - would be nice for userspace libraries if at least all aircraft
>> had a similar 'default orientation'.
> As you said earlier, things are never that simple. The standard orientation
> may vary with types of UAVs (quad-rotor, fixed wings, bizarre home made UFOs...)
Sure, but let's document what we can so at least some cases are covered
>> For the more 'standard' device with a screen I think we would want to standardise
>> if at all possible.  Most hand held devices have a 'natural' orientation
>> (front facing camera at the top for example).  In those cases we are basically looking
>> at whether the sensor is mounted on the back or the front of the main circuit board and
>> then of course it can be at any rotation in plane but typically is at 90 degrees
>> (hence the inv mpu limitations)
>>
>> I'm guessing there are existing userspace mappings for this.  Perhaps in the Gnome
>> sensors stuff?
> [snip...]
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