[v3 00/13] Add support for Bosch BNO055 IMU

Andrea Merello
2022-02-17T16:27:25Z

This series (tries to) add support for Bosch BNO055 IMU to Linux IIO
subsystem. It is made up several patches:

1/13 to 6/13: add some IIO modifiers, and their documentation, to the IIO
core layer, in order to being able to expose the linear
acceleration and Euler angles among standard attributes.
Also update the IIO event monitor tool

6/13 to 10/13: add the core IIO BNO055 driver documentation for sysfs
attributes and DT bindings

11/13: adds serdev BNO055 driver to actually use the IMU via serial line

12/13: adds I2C BNO055 driver to actually use the IMU via I2C wiring

13/13: add a documentation file that describe the bno055 driver and
specifically the calibration

Differences wrt v2:

FIXES:
- workaround: switching off and on fusion mode could cause IMU to
misbehave (i.e. wrong anglvel data)
- FIX sometimes driver failed to write attributes / manual settings
were not honored
- workaround: for IMU gyroscope unit bug (unit change by changing range)
- Fixed some typos bosh->bosch
- Fixed warning caught by kernel robot
- Fix bursting was broken
- Fix missing mutex unlock in exit path

API:
- rework sysfs attribute names
- change linear acceleration modifiers names (e.g. ACCEL_LINEAR_MOD ->
ACCEL_MOD)
- 'unique_id' sysfs attribute become 'serial_number' and become
non-bno055-specific
- fix range units and sysfs names
- fix gyro lpf available values were returned in twisted order
- gyroscope no longer has the range attribute, the scale can now be
changed instead

Misc:
- Dropped previous patch 01 (add find_closest_unsorted) as it is not
needed anymore
- Some trivial stuff (commas, newlines etc)
- Added help section in Kconfig
- reworked sysfs attribute code, to easier implement required API changes
and above fixes
- hopefully implement all reviewers advice (e.g. rid of macro helpers,
kill useless devm primitive, simplify bno055_clk_disable, rework some
bail-out code, conditions check, remove odd usage of ternary operator,
move default clause at end of switch block, etc ..)
- reorder patches so that DOC for a new thing come after patch that
introduced that thing
- linear acceleration DOC moved and cross-referenced to acceleration doc

Differences wrt other BNO055 drivers:

Previously at least another driver for the very same chip has been posted
to the Linux ML [0], but it has been never merged, and it seems no one
cared of it since quite a long time.

This driver differs from the above driver on the following aspects:

- This driver supports also serial access (to be reliable, reset pin is
required to be wired)

- The above driver tried to support all IMU HW modes by allowing to
choose one in the DT, and adapting IIO attributes accordingly. This
driver does not rely on DT for this, instead settings are done via
sysfs attributes. All IIO attributes are always exposed; more on this
later on. This driver however supports only a subset of the
HW-supported modes.

- This driver has some support for managing the IMU calibration

Supported operation modes:

- AMG (accelerometer, magnetometer and gyroscope) mode, which provides
raw (uncalibrated) measurements from the said sensors, and allows for
setting some parameters about them (e.g. filter cut-off frequency, max
sensor ranges, etc).

- Fusion mode, which still provides AMG measures, while it also provides
other data calculated by the IMU (e.g. rotation angles, linear
acceleration, etc). In this mode user has no freedom to set any sensor
parameter, since the HW locks them. Autocalibration and correction is
performed by the IMU.

IIO attributes exposing sensors parameters are always present, but in
fusion modes the available values are constrained to just the one used by
the HW. This is reflected in the '*_available' IIO attributes.

Trying to set a not-supported value always falls back to the closest
supported one, which in this case is just the one in use by the HW.

IIO attributes for unavailable measurements (e.g. Euler angles in AMG
mode) just read zero (which is consistent WRT what you get when reading
from a buffer with those attributes enabled).

IMU calibration:

The IMU supports for two sets of calibration parameters:

- SIC matrix. user-provided; this driver doesn't currently support it

- Offset and radius parameters. The IMU automatically finds out them when
it is running in fusion mode; supported by this driver.

The driver provides access to autocalibration flags (i.e. you can known
if the IMU has successfully autocalibrated) and to calibration data blob.
The user can save this blob in a "firmware" file (i.e. in /lib/firmware)
that the driver looks for at probe time. If found, then the IMU is
initialized with this calibration data. This saves the user from
performing the calibration procedure every time (which consist of moving
the IMU in various way).

The driver looks for calibration data file using two different names:
first a file whose name is suffixed with the IMU unique ID is searched
for; this is useful when there is more than one IMU instance. If this
file is not found, then a "generic" calibration file is searched for
(which can be used when only one IMU is present, without struggling with
fancy names, that changes on each device).

In AMG mode the IIO 'offset' attributes provide access to the offsets
from calibration data (if any), so that the user can apply them to the
accel, angvel and magn IIO attributes. In fusion mode they are not needed
and read as zero.

Access protocols and serdev module:

The serial protocol is quite simple, but there are tricks to make it
really works. Those tricks and workarounds are documented in the driver
source file.

The core BNO055 driver tries to group readings in burst when appropriate,
in order to optimize triggered buffer operation. The threshold for
splitting a burst (i.e. max number of unused bytes in the middle of a
burst that will be throw away) is provided to the core driver by the
lowlevel access driver (either serdev or I2C) at probe time.

[0] https://www.spinics.net/lists/linux-iio/msg25508.html

Andrea Merello (13):
iio: add modifiers for linear acceleration
iio: document linear acceleration modifiers
iio: event_monitor: add linear acceleration modifiers
iio: add modifers for pitch, yaw, roll
iio: document pitch, yaw, roll modifiers
iio: event_monitor: add pitch, yaw and roll modifiers
iio: imu: add Bosch Sensortec BNO055 core driver
iio: document bno055 private sysfs attributes
iio: document "serial_number" sysfs attribute
dt-bindings: iio: imu: add documentation for Bosch BNO055 bindings
iio: imu: add BNO055 serdev driver
iio: imu: add BNO055 I2C driver
docs: iio: add documentation for BNO055 driver

Documentation/ABI/testing/sysfs-bus-iio | 25 +
.../ABI/testing/sysfs-bus-iio-bno055 | 81 +
.../bindings/iio/imu/bosch,bno055.yaml | 59 +
Documentation/iio/bno055.rst | 53 +
drivers/iio/imu/Kconfig | 1 +
drivers/iio/imu/Makefile | 1 +
drivers/iio/imu/bno055/Kconfig | 25 +
drivers/iio/imu/bno055/Makefile | 5 +
drivers/iio/imu/bno055/bno055.c | 1612 +++++++++++++++++
drivers/iio/imu/bno055/bno055.h | 12 +
drivers/iio/imu/bno055/bno055_i2c.c | 50 +
drivers/iio/imu/bno055/bno055_sl.c | 557 ++++++
drivers/iio/industrialio-core.c | 6 +
include/uapi/linux/iio/types.h | 7 +-
tools/iio/iio_event_monitor.c | 6 +
15 files changed, 2499 insertions(+), 1 deletion(-)
create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-bno055
create mode 100644 Documentation/devicetree/bindings/iio/imu/bosch,bno055.yaml
create mode 100644 Documentation/iio/bno055.rst
create mode 100644 drivers/iio/imu/bno055/Kconfig
create mode 100644 drivers/iio/imu/bno055/Makefile
create mode 100644 drivers/iio/imu/bno055/bno055.c
create mode 100644 drivers/iio/imu/bno055/bno055.h
create mode 100644 drivers/iio/imu/bno055/bno055_i2c.c
create mode 100644 drivers/iio/imu/bno055/bno055_sl.c

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2.17.1