[RFC PATCH v1 0/3] iio sensor mounting matrix support

[Gregor Boirie <gregor.boirie-ITF29qwbsa/QT0dZR+AlfA@public.gmane.org>]

This RFC patch series follows up on Rob Herring and Jonathan Cameron comments
about ak8975 magnetometer mounting matrix support. Thread starts here:
http://www.spinics.net/lists/linux-iio/msg23505.html

As a recall, we want to expose a rotation matrix to indicate userspace the chip
placement with respect to the overall hardware system. This allows an
application to adjust coordinates sampled from a sensor chip when its position
deviates from the main hardware system.
Rob mentionned that the interface could be appropriate for other sensors such as
gyro, accelero, etc... This would prevent from "ending up with a bunch of
similar yet different interfaces".

Requirements:
1. delegate computation to userspace ;
2. floating point arithmetics support ;
3. per sample type matrix ;
4. remain compliant with legacy interface (mpu6050).

Point 1. above allows application to perform arbitrary transformations in
addition to sensor alignment handling.
Point 2. is required for flexible chip positioning.
Point 3. comes from the fact that chips, such as ADIS16407, may implement
different axis direction references for each measurement space.
See http://www.analog.com/media/en/technical-documentation/data-sheets/ADIS16407.pdf

Firs patch attached raise several questions for which I'd like to hear your
suggestions.

>From point 3. above, we should end up with something like the following for a
a magneto + gyro + accelero chip :
iio:deviceX/in_anglvel_mount_matrix, applicable to all 3 gyro channels
iio:deviceX/in_accel_mount_matrix, applicable to all 3 accelero channels
iio:deviceX/in_magn_mount_matrix, applicable to all 3 magneto channels

Do we need to ensure proper naming consistency for sysfs attributes ? How ?
Reuse iio_chan_type_name_spec array ?

Should we limit matrix sysfs attribute instantiation to a subset of sensor
types ? Which ones ? Or should we leave this to driver writers choice ?

Last patch relates to mpu6050 mounting matrix evolutions : legacy attribute was
extracted from platform_data. For sake of simplicity and as platform data
mechanism is becoming more and more "obsolete", I implemented new mounting
matrix API support for device-tree nodes only. Good enought ?

Best regards,
gregor.

Gregor Boirie (3):
  iio:core: mounting matrix support
  iio:ak8975: add mounting matrix support
  iio:imu:mpu6050: enhance mounting matrix support

 Documentation/ABI/testing/sysfs-bus-iio            | 51 ++++++++++++++
 .../devicetree/bindings/iio/imu/inv_mpu6050.txt    | 13 ++++
 .../bindings/iio/magnetometer/ak8975.txt           | 10 +++
 drivers/iio/imu/inv_mpu6050/inv_mpu_core.c         | 56 +++++++++++++--
 drivers/iio/imu/inv_mpu6050/inv_mpu_iio.h          |  4 +-
 drivers/iio/industrialio-core.c                    | 81 ++++++++++++++++++++++
 drivers/iio/magnetometer/ak8975.c                  | 40 ++++++++++-
 include/linux/iio/magnetometer/ak8975.h            | 16 +++++
 include/linux/iio/sysfs.h                          | 25 +++++++
 include/linux/platform_data/invensense_mpu6050.h   |  5 +-
 10 files changed, 293 insertions(+), 8 deletions(-)
 create mode 100644 include/linux/iio/magnetometer/ak8975.h

-- 
2.1.4

--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html