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| author | Mehdi Djait <mehdi.djait@linux.intel.com> | 2025-06-26 15:33:53 +0200 |
|---|---|---|
| committer | Hans Verkuil <hverkuil+cisco@kernel.org> | 2025-08-13 15:10:19 +0200 |
| commit | e2b1ebd72c81ca7bcceb0ed2cea2200978b6e975 (patch) | |
| tree | 59a78dfc4a463eac70c57803e5e2ee17851ba855 | |
| parent | 2d240b124cc9df62ccccee6054bc3d1d19018758 (diff) | |
| download | net-e2b1ebd72c81ca7bcceb0ed2cea2200978b6e975.tar.gz | |
Documentation: media: camera-sensor: Mention v4l2_devm_sensor_clk_get() for obtaining the clock
Add the new v4l2 helper devm_v4l2_sensor_clk_get() to Documentation. the
helper works on both DT- and ACPI-based platforms to retrieve a
reference to the clock producer from firmware.
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mehdi Djait <mehdi.djait@linux.intel.com>
Co-developed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>
| -rw-r--r-- | Documentation/driver-api/media/camera-sensor.rst | 24 |
1 files changed, 17 insertions, 7 deletions
diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst index c290833165e67a..94bd1dae82d5c5 100644 --- a/Documentation/driver-api/media/camera-sensor.rst +++ b/Documentation/driver-api/media/camera-sensor.rst @@ -29,21 +29,31 @@ used in the system. Using another frequency may cause harmful effects elsewhere. Therefore only the pre-determined frequencies are configurable by the user. +The external clock frequency shall be retrieved by obtaining the external clock +using the ``devm_v4l2_sensor_clk_get()`` helper function, and then getting its +frequency with ``clk_get_rate()``. Usage of the helper function guarantees +correct behaviour regardless of whether the sensor is integrated in a DT-based +or ACPI-based system. + ACPI ~~~~ -Read the ``clock-frequency`` _DSD property to denote the frequency. The driver -can rely on this frequency being used. +ACPI-based systems typically don't register the sensor external clock with the +kernel, but specify the external clock frequency in the ``clock-frequency`` +_DSD property. The ``devm_v4l2_sensor_clk_get()`` helper creates and returns a +fixed clock set at that rate. Devicetree ~~~~~~~~~~ -The preferred way to achieve this is using ``assigned-clocks``, -``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See the -`clock device tree bindings +Devicetree-based systems declare the sensor external clock in the device tree +and reference it from the sensor node. The preferred way to select the external +clock frequency is to use the ``assigned-clocks``, ``assigned-clock-parents`` +and ``assigned-clock-rates`` properties in the sensor node to set the clock +rate. See the `clock device tree bindings <https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml>`_ -for more information. The driver then gets the frequency using -``clk_get_rate()``. +for more information. The ``devm_v4l2_sensor_clk_get()`` helper retrieves and +returns that clock. This approach has the drawback that there's no guarantee that the frequency hasn't been modified directly or indirectly by another driver, or supported by |