libcamera: add model() for retrieving model name in V4L2Subdevice

CameraSensor retrieves model name from media entity. Move the heuristics
method into V4L2Subdevice, so CameraLens can reuse the function.

Signed-off-by: Han-Lin Chen <hanlinchen@chromium.org>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/internal/v4l2_subdevice.h

@@ -61,6 +61,8 @@ public:
 	int setFormat(unsigned int pad, V4L2SubdeviceFormat *format,
 		      Whence whence = ActiveFormat);
 
+	const std::string &model();
+
 	static std::unique_ptr<V4L2Subdevice>
 	fromEntityName(const MediaDevice *media, const std::string &entity);
 
@@ -75,6 +77,8 @@ private:
 					    unsigned int code);
 
 	const MediaEntity *entity_;
+
+	std::string model_;
 };
 
 } /* namespace libcamera */

src/libcamera/camera_sensor.cpp

@@ -13,7 +13,6 @@
 #include <iomanip>
 #include <limits.h>
 #include <math.h>
-#include <regex>
 #include <string.h>
 
 #include <libcamera/property_ids.h>
@@ -347,34 +346,7 @@ void CameraSensor::initTestPatternModes(
 
 int CameraSensor::initProperties()
 {
-	/*
-	 * Extract the camera sensor model name from the media entity name.
-	 *
-	 * There is no standardized naming scheme for sensor entities in the
-	 * Linux kernel at the moment.
-	 *
-	 * - The most common rule, used by I2C sensors, associates the model
-	 *   name with the I2C bus number and address (e.g. 'imx219 0-0010').
-	 *
-	 * - When the sensor exposes multiple subdevs, the model name is
-	 *   usually followed by a function name, as in the smiapp driver (e.g.
-	 *   'jt8ew9 pixel_array 0-0010').
-	 *
-	 * - The vimc driver names its sensors 'Sensor A' and 'Sensor B'.
-	 *
-	 * Other schemes probably exist. As a best effort heuristic, use the
-	 * part of the entity name before the first space if the name contains
-	 * an I2C address, and use the full entity name otherwise.
-	 */
-	std::string entityName = entity_->name();
-	std::regex i2cRegex{ " [0-9]+-[0-9a-f]{4}" };
-	std::smatch match;
-
-	if (std::regex_search(entityName, match, i2cRegex))
-		model_ = entityName.substr(0, entityName.find(' '));
-	else
-		model_ = entityName;
-
+	model_ = subdev_->model();
 	properties_.set(properties::Model, utils::toAscii(model_));
 
 	/* Generate a unique ID for the sensor. */
@@ -832,7 +804,7 @@ int CameraSensor::generateId()
 	/*
 	 * Virtual sensors not described in firmware
 	 *
-	 * Verify it's a platform device and construct ID from the deive path
+	 * Verify it's a platform device and construct ID from the device path
 	 * and model of sensor.
 	 */
 	if (devPath.find("/sys/devices/platform/", 0) == 0) {

src/libcamera/v4l2_subdevice.cpp

@@ -9,6 +9,7 @@
 
 #include <fcntl.h>
 #include <iomanip>
+#include <regex>
 #include <sstream>
 #include <string.h>
 #include <sys/ioctl.h>
@@ -442,6 +443,58 @@ int V4L2Subdevice::setFormat(unsigned int pad, V4L2SubdeviceFormat *format,
 	return 0;
 }
 
+/**
+ * \brief Retrieve the model name of the device
+ *
+ * The model name allows identification of the specific device model. This can
+ * be used to infer device characteristics, for instance to determine the
+ * analogue gain model of a camera sensor based on the sensor model name.
+ *
+ * Neither the V4L2 API nor the Media Controller API expose an explicit model
+ * name. This function implements a heuristics to extract the model name from
+ * the subdevice's entity name. This should produce accurate results for
+ * I2C-based devices. If the heuristics can't match a known naming pattern,
+ * the function returns the full entity name.
+ *
+ * \return The model name of the device
+ */
+const std::string &V4L2Subdevice::model()
+{
+	if (!model_.empty())
+		return model_;
+
+	/*
+	 * Extract model name from the media entity name.
+	 *
+	 * There is no standardized naming scheme for sensor or other entities
+	 * in the Linux kernel at the moment.
+	 *
+	 * - The most common rule, used by I2C sensors, associates the model
+	 *   name with the I2C bus number and address (e.g. 'imx219 0-0010').
+	 *
+	 * - When the sensor exposes multiple subdevs, the model name is
+	 *   usually followed by a function name, as in the smiapp driver (e.g.
+	 *   'jt8ew9 pixel_array 0-0010').
+	 *
+	 * - The vimc driver names its sensors 'Sensor A' and 'Sensor B'.
+	 *
+	 * Other schemes probably exist. As a best effort heuristic, use the
+	 * part of the entity name before the first space if the name contains
+	 * an I2C address, and use the full entity name otherwise.
+	 */
+	std::string entityName = entity_->name();
+	std::regex i2cRegex{ " [0-9]+-[0-9a-f]{4}" };
+	std::smatch match;
+
+	std::string model;
+	if (std::regex_search(entityName, match, i2cRegex))
+		model_ = entityName.substr(0, entityName.find(' '));
+	else
+		model_ = entityName;
+
+	return model_;
+}
+
 /**
  * \brief Create a new video subdevice instance from \a entity in media device
  * \a media