[PATCH RFC 0/3] iio: add Open Sensor Fusion UART driver

[Jinseob Kim]

Open Sensor Fusion is a UART-attached sensor aggregation device. The current
prototype sends OSF protocol v0 frames over a host UART link. This RFC adds the
first Linux IIO receive path for that UART stream.

The first transport is serdev UART. USB, real sensor reads, fusion output, and
production timestamp correlation are intentionally left out of this series.

The driver code is kept in one patch for the first RFC to avoid intermediate
non-buildable states. The internal files are still split by protocol, stream,
core, transport, and IIO code.

Current validation coverage:

- STM32F405 test firmware OSF protocol v0 UART stream at 115200 8N1.
- Raspberry Pi 4 serdev probe and receive path to osf_core_receive_frame().
- CAPABILITY_REPORT-driven IIO device registration.
- IIO read_raw for accel, gyro, magn, and temp samples.
- IIO software kfifo buffer userspace read.
- scan decode helper for buffered samples.
- dt_binding_check pass for the binding.
- checkpatch.pl --strict with ERROR 0, WARNING 0, CHECK 0.
- W=1 source compile/link phase clean in the staging kernel tree.
- modpost unresolved symbol warnings came from the staging tree missing
  Module.symvers.

Known limits:

- The sample source is synthetic stream data, not real ICM-42688-P or MMC5983MA
  sensor reads.
- The IIO timestamp is Linux host receive time. Device time correlation is still
  open.
- Runtime capability removal is not implemented.
- The staging layout uses drivers/iio/opensensorfusion/. The final directory is
  open for review.

Review feedback wanted on the IIO device layout, timestamp policy, binding
shape, and driver directory.

Jinseob Kim (3):
  dt-bindings: iio: imu: add Open Sensor Fusion UART binding
  iio: osf: add Open Sensor Fusion UART IIO driver
  MAINTAINERS: add Open Sensor Fusion IIO driver entry

 .../iio/imu/opensensorfusion,osf-uart.yaml    |  33 ++
 MAINTAINERS                                   |   7 +
 drivers/iio/Kconfig                           |   1 +
 drivers/iio/Makefile                          |   1 +
 drivers/iio/opensensorfusion/Kconfig          |  15 +
 drivers/iio/opensensorfusion/Makefile         |   6 +
 drivers/iio/opensensorfusion/osf_core.c       | 334 +++++++++++++++++
 drivers/iio/opensensorfusion/osf_core.h       |  81 ++++
 drivers/iio/opensensorfusion/osf_iio.c        | 268 +++++++++++++
 drivers/iio/opensensorfusion/osf_iio.h        |  21 ++
 drivers/iio/opensensorfusion/osf_protocol.c   | 234 ++++++++++++
 drivers/iio/opensensorfusion/osf_protocol.h   | 100 +++++
 drivers/iio/opensensorfusion/osf_serdev.c     | 354 ++++++++++++++++++
 drivers/iio/opensensorfusion/osf_serdev.h     |   8 +
 drivers/iio/opensensorfusion/osf_stream.c     | 212 +++++++++++
 drivers/iio/opensensorfusion/osf_stream.h     |  31 ++
 16 files changed, 1706 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/imu/opensensorfusion,osf-uart.yaml
 create mode 100644 drivers/iio/opensensorfusion/Kconfig
 create mode 100644 drivers/iio/opensensorfusion/Makefile
 create mode 100644 drivers/iio/opensensorfusion/osf_core.c
 create mode 100644 drivers/iio/opensensorfusion/osf_core.h
 create mode 100644 drivers/iio/opensensorfusion/osf_iio.c
 create mode 100644 drivers/iio/opensensorfusion/osf_iio.h
 create mode 100644 drivers/iio/opensensorfusion/osf_protocol.c
 create mode 100644 drivers/iio/opensensorfusion/osf_protocol.h
 create mode 100644 drivers/iio/opensensorfusion/osf_serdev.c
 create mode 100644 drivers/iio/opensensorfusion/osf_serdev.h
 create mode 100644 drivers/iio/opensensorfusion/osf_stream.c
 create mode 100644 drivers/iio/opensensorfusion/osf_stream.h

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2.43.0