libcamera: Move IPA sensor controls validation to CameraSensor

The CameraSensor class validates that the sensor driver in use supports
the controls required for IPA modules to work correctly.

For in-tree IPA modules, whose pipeline handlers already use
CameraSensor there's no need to validate such controls again.

Remove controls validation from the IPU3 and RkISP1 IPA modules and rely
on CameraSensor doing that at initialization time.

The list of mandatory controls is expanded to add V4L2_CID_ANALOGUE_GAIN
without which IPA modules cannot function.

The new requirement only applies to RAW sensors, platforms like UVC and
Simple are not impacted by this change.

While at it, expand the sensor driver requirements documentation to
include V4L2_ANALOGUE_GAIN in the list of mandatory controls a sensor
driver has to support.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

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

src/ipa/ipu3/ipu3.cpp

@@ -171,8 +171,6 @@ private:
 			    ControlInfoMap *ipaControls);
 	void updateSessionConfiguration(const ControlInfoMap &sensorControls);
 
-	bool validateSensorControls();
-
 	void setControls(unsigned int frame);
 	void calculateBdsGrid(const Size &bdsOutputSize);
 
@@ -292,28 +290,6 @@ void IPAIPU3::updateControls(const IPACameraSensorInfo &sensorInfo,
 	*ipaControls = ControlInfoMap(std::move(controls), controls::controls);
 }
 
-/**
- * \brief Validate that the sensor controls mandatory for the IPA exists
- */
-bool IPAIPU3::validateSensorControls()
-{
-	static const uint32_t ctrls[] = {
-		V4L2_CID_ANALOGUE_GAIN,
-		V4L2_CID_EXPOSURE,
-		V4L2_CID_VBLANK,
-	};
-
-	for (auto c : ctrls) {
-		if (sensorCtrls_.find(c) == sensorCtrls_.end()) {
-			LOG(IPAIPU3, Error) << "Unable to find sensor control "
-					    << utils::hex(c);
-			return false;
-		}
-	}
-
-	return true;
-}
-
 /**
  * \brief Initialize the IPA module and its controls
  *
@@ -512,11 +488,6 @@ int IPAIPU3::configure(const IPAConfigInfo &configInfo,
 
 	calculateBdsGrid(configInfo.bdsOutputSize);
 
-	if (!validateSensorControls()) {
-		LOG(IPAIPU3, Error) << "Sensor control validation failed.";
-		return -EINVAL;
-	}
-
 	/* Update the camera controls using the new sensor settings. */
 	updateControls(sensorInfo_, sensorCtrls_, ipaControls);
 

src/ipa/rkisp1/rkisp1.cpp

@@ -215,20 +215,10 @@ int IPARkISP1::configure([[maybe_unused]] const IPACameraSensorInfo &info,
 	ctrls_ = entityControls.at(0);
 
 	const auto itExp = ctrls_.find(V4L2_CID_EXPOSURE);
-	if (itExp == ctrls_.end()) {
-		LOG(IPARkISP1, Error) << "Can't find exposure control";
-		return -EINVAL;
-	}
-
-	const auto itGain = ctrls_.find(V4L2_CID_ANALOGUE_GAIN);
-	if (itGain == ctrls_.end()) {
-		LOG(IPARkISP1, Error) << "Can't find gain control";
-		return -EINVAL;
-	}
-
 	int32_t minExposure = itExp->second.min().get<int32_t>();
 	int32_t maxExposure = itExp->second.max().get<int32_t>();
 
+	const auto itGain = ctrls_.find(V4L2_CID_ANALOGUE_GAIN);
 	int32_t minGain = itGain->second.min().get<int32_t>();
 	int32_t maxGain = itGain->second.max().get<int32_t>();
 

src/libcamera/camera_sensor.cpp

@@ -301,6 +301,7 @@ int CameraSensor::validateSensorDriver()
 	 * required by the CameraSensor class.
 	 */
 	static constexpr uint32_t mandatoryControls[] = {
+		V4L2_CID_ANALOGUE_GAIN,
 		V4L2_CID_EXPOSURE,
 		V4L2_CID_HBLANK,
 		V4L2_CID_PIXEL_RATE,