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-rw-r--r--Documentation/sensor_driver_requirements.rst7
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/sensor_driver_requirements.rst b/Documentation/sensor_driver_requirements.rst
index b0854be3..3abc8f35 100644
--- a/Documentation/sensor_driver_requirements.rst
+++ b/Documentation/sensor_driver_requirements.rst
@@ -24,16 +24,23 @@ The sensor driver is assumed to be fully compliant with the V4L2 specification.
For RAW sensors, the sensor driver shall support the following V4L2 controls:
+* `V4L2_CID_ANALOGUE_GAIN`_
* `V4L2_CID_EXPOSURE`_
* `V4L2_CID_HBLANK`_
* `V4L2_CID_PIXEL_RATE`_
* `V4L2_CID_VBLANK`_
+.. _V4L2_CID_ANALOGUE_GAIN: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
.. _V4L2_CID_EXPOSURE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/control.html
.. _V4L2_CID_HBLANK: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
.. _V4L2_CID_PIXEL_RATE: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-process.html
.. _V4L2_CID_VBLANK: https://www.kernel.org/doc/html/latest/userspace-api/media/v4l/ext-ctrls-image-source.html
+The ``ANALOGUE_GAIN`` control units are sensor-specific. libcamera requires
+a sensor-specific CameraSensorHelper implementation to translate between the
+sensor specific ``gain code`` and the analogue ``gain value`` expressed as an
+absolute number as defined by ``controls::AnalogueGain``.
+
While V4L2 doesn't specify a unit for the ``EXPOSURE`` control, libcamera
requires it to be expressed as a number of image lines. Camera sensor drivers
that do not comply with this requirement will need to be adapted or will produce