Hi Rob, On Mon, Mar 21, 2016 at 09:58:46AM -0500, Rob Herring wrote: > On Thu, Mar 17, 2016 at 11:43 AM, Gregor Boirie > <gregor.boirie@xxxxxxxxxx> 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? 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. > > 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 ? > > > 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" ? > > Rob > > [1] https://groups.google.com/forum/#!msg/android-x86/LaKhV8cT69o/G1rrVU0_JAAJ -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
