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

[Gregor Boirie <gregor.boirie@parrot.com>]

On 03/28/2016 05:03 PM, Jonathan Cameron wrote:

[snip...]

>
> Why is the sysfs interface specific to ak8975?
>>> AFAIK, this is just the first IIO driver implementation relying on floating
>>> point numbers. Should a single driver be enough to justify a "generic" API,
>>> I suppose code could be factored out in a similar way to over sampling rate
>>> support. People could call this on a per-driver basis.
>> Given it is an ABI, yes I think so. We don't want to end up with a
>> bunch of similar yet different interfaces.
>>
> Absolutely.  Most interfaces get made up based on one implementation ;)
> A second is always nice, but here the interface is obvious enough we don't
> need to wait.
Right. I'll post a separate patch then.
>>>> 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].
>>> Same may apply to gyro / accelero / imu and magnetometers at least.
>>> inv_mpu_core.c already implements such a rotation matrix exposed as 3x3 integers
>>> array. Should we be smart enough to keep this compatible with existing userspace
>>> apps ?
>> You have to maintain the ABI. If both interfaces can co-exist, then
>> you can have both and mark the old one as deprecated. In time we can
>> remove the old one.
> If you want to (or someone else does) it would be good to add the new abi to
> inv_mpu_core as well and indeed mark the old one as deprecated.
> The cost of keeping it is negligible, so we may never actually bother to
> remove it.
What's the better way to mark this as deprecated ? dev_warn() ? 
__deprecated ?
Anything else ?
>>>>> 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.
>>> What about "mounting-matrix" ?
>> Sure.
> Works for me as well.
>> Rob
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>