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Fri, 18 Sep 2026 11:25:33 -0700 (PDT) From: Jinseob Kim To: jic23@kernel.org, linux-iio@vger.kernel.org Cc: dlechner@baylibre.com, nuno.sa@analog.com, andriy.shevchenko@intel.com, linux-kernel@vger.kernel.org, rdunlap@infradead.org, joshua.crofts1@gmail.com, u.kleine-koenig@baylibre.com, julianbraha@gmail.com, robh@kernel.org, krzk+dt@kernel.org, conor+dt@kernel.org, devicetree@vger.kernel.org, corbet@lwn.net, skhan@linuxfoundation.org, linux-doc@vger.kernel.org Subject: [PATCH v10 2/8] Documentation: iio: add Open Sensor Fusion driver overview Date: Sat, 19 Sep 2026 03:24:40 +0900 Message-ID: <9fdbc924bf3387a4d33d1258ea21ac33abef65bb.1789753020.git.kimjinseob88@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Document the supported OSF receiver profile, runtime sensor discovery, IIO channel units, scale validation and session lifetime. Link the project-maintained fixed wire specification instead of duplicating its layouts and compatibility policy. Explain host IIO timestamps and the explicit rebind needed after a changed inventory. Assisted-by: LLM Signed-off-by: Jinseob Kim --- Documentation/iio/index.rst | 1 + Documentation/iio/open-sensor-fusion.rst | 77 ++++++++++++++++++++++++ MAINTAINERS | 1 + 3 files changed, 79 insertions(+) create mode 100644 Documentation/iio/open-sensor-fusion.rst diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst index b02b879b053a..c2b7963348fd 100644 --- a/Documentation/iio/index.rst +++ b/Documentation/iio/index.rst @@ -40,4 +40,5 @@ Industrial I/O Kernel Drivers adxl345 bno055 ep93xx_adc + open-sensor-fusion opt4060 diff --git a/Documentation/iio/open-sensor-fusion.rst b/Documentation/iio/open-sensor-fusion.rst new file mode 100644 index 000000000000..03ab36aca5f8 --- /dev/null +++ b/Documentation/iio/open-sensor-fusion.rst @@ -0,0 +1,77 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +Open Sensor Fusion +================== + +Open Sensor Fusion is a sensor aggregation hub interface. The Linux IIO driver +receives device-to-host frames over UART and discovers sensor channels from +capability reports. Device Tree describes the hub using the +``opensensorfusion,osf`` compatible; individual sensors are discovered at +runtime. See the binding in +``Documentation/devicetree/bindings/iio/opensensorfusion,osf.yaml``. + +The OSF Device-to-Host 0.0 specification is maintained by the Open Sensor Fusion +project. The canonical specification_ defines the wire layout, compatibility +rules, reserved fields and physical units. This document describes the Linux +receiver profile and its mapping to IIO. + +.. _specification: https://github.com/opensensorfusion/opensensorfusion-protocol/blob/ca9cdea1ae550c2b4d6f29f87877adae99470744/spec/osf-d2h-0.0.md + +Supported receive profile +------------------------- + +The driver supports the fixed OSF0 frame layout with protocol major version 0. +Compatible minor versions use the same known message layouts. The decoder +requires exact lengths for known messages, validates CRC and bounds before +interpreting payloads, and tolerates reserved padding. Unsupported majors and +unknown message types are ignored. Unsupported capability entries are skipped +individually. A CRC-valid application rejection consumes the complete frame; +an invalid frame candidate is resynchronized without trusting its payload length. + +The receive path handles sensor samples, complete capability reports and +device status. Its limits are 4096 bytes per frame and 16 supported sensor +descriptors. These are implementation limits, not protocol-wide maxima. + +IIO mapping +----------- + +The supported sensor classes map to: + +* accelerometer: ``IIO_ACCEL`` X/Y/Z, in m/s^2; +* gyroscope: ``IIO_ANGL_VEL`` X/Y/Z, in rad/s; +* magnetometer: ``IIO_MAGN`` X/Y/Z, in gauss; +* temperature: ``IIO_TEMP``, in millidegrees Celsius. + +Each registered channel exposes signed ``RAW`` data and descriptor-derived +``SCALE``. Multiplying RAW by SCALE gives a value in the channel's IIO unit. +Buffered samples use signed 32-bit values with native CPU endianness. Active +channels are packed into the scan, with initialized padding before an optional +64-bit timestamp. + +Discovery and session lifetime +------------------------------ + +The driver validates all supported descriptors before registering IIO devices. +An empty or entirely unsupported initial report leaves discovery open for a +later supported report. Supported descriptors must advertise a nonzero scale. +A sample's channel count, format and scale must match its registered descriptor +before it can update the latest RAW cache or be published to a buffer. A +rejected sample preserves previously accepted data. + +Repeated reports are compared by sensor type and index, independently of entry +order. Reserved padding, advisory flags and unsupported additions do not change +the supported inventory. A supported key appearing or disappearing, or a +change in its channel count, format or scale, faults the bound session. + +After a session fault, new cache updates and buffer publication stop, and +direct RAW reads fail. Existing IIO devices remain until driver teardown. +An equivalent report does not clear the fault; explicit unbind/rebind starts +fresh discovery. No fault-specific userspace ABI is exposed. + +Timestamps +---------- + +Buffered samples use the selected IIO host clock when they are pushed into +the buffer. The device timestamp is not correlated with that clock and is not +used as the IIO buffer timestamp. Device timestamp or sequence discontinuities +alone do not start a new host session. diff --git a/MAINTAINERS b/MAINTAINERS index 9463b8111d52..26b9b2862724 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -20515,6 +20515,7 @@ OPEN SENSOR FUSION M: Jinseob Kim S: Maintained F: Documentation/devicetree/bindings/iio/opensensorfusion,osf.yaml +F: Documentation/iio/open-sensor-fusion.rst K: opensensorfusion OPENCOMPUTE PTP CLOCK DRIVER -- 2.43.0