Re: [PATCH v3 2/3] iio:magnetometer:ak8975: mounting matrix support
From: Rob Herring <hidden>
Date: 2016-03-21 14:58:46
Also in:
linux-iio
On Thu, Mar 17, 2016 at 11:43 AM, Gregor Boirie [off-list ref] 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].
quoted hunk
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