On Mon, Mar 21, 2016 at 5:21 PM, Gregor Boirie <gregor.boirie@xxxxxxxxxx> wrote: > 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. Given it is an ABI, yes I think so. We don't want to end up with a bunch of similar yet different interfaces. >> 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. >> > 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. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
