[libcamera-devel] [PATCH v3 2/5] libcamera: camera_sensor: Generate a sensor ID

[Niklas Söderlund]

Generate a constant and unique string ID for the sensor. The ID is
generated from firmware information fetched from the hardware that backs
the sensor. The ID is unique and persistent across reboots of the
system.

For OF based systems the ID is the full path of the sensors in the
device tree description. For ACPI bases systems the ID is the ACPI
firmware nodes path. Both ID sources are guaranteed to be unique and
persistent as long as the firmware of the system is not changed.

A special case is needed to deal with the VIMC pipeline that implements
a virtual pipeline that is not backed by any hardware device and is
therefore not described in the device firmware.

Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
 include/libcamera/internal/camera_sensor.h |  4 +
 src/libcamera/camera_sensor.cpp            | 85 ++++++++++++++++++++++
 2 files changed, 89 insertions(+)

diff --git a/include/libcamera/internal/camera_sensor.h b/include/libcamera/internal/camera_sensor.h
index 06c8292ca30129de..e0d2d9f63b47c2fe 100644
--- a/include/libcamera/internal/camera_sensor.h
+++ b/include/libcamera/internal/camera_sensor.h
@@ -47,6 +47,7 @@ public:
 	int init();
 
 	const std::string &model() const { return model_; }
+	const std::string &id() const { return id_; }
 	const MediaEntity *entity() const { return entity_; }
 	const std::vector<unsigned int> &mbusCodes() const { return mbusCodes_; }
 	const std::vector<Size> &sizes() const { return sizes_; }
@@ -67,11 +68,14 @@ protected:
 	std::string logPrefix() const override;
 
 private:
+	int generateID();
+
 	const MediaEntity *entity_;
 	std::unique_ptr<V4L2Subdevice> subdev_;
 	unsigned int pad_;
 
 	std::string model_;
+	std::string id_;
 
 	V4L2Subdevice::Formats formats_;
 	Size resolution_;
diff --git a/src/libcamera/camera_sensor.cpp b/src/libcamera/camera_sensor.cpp
index 350f49accad99c7b..a4339759bc847ff0 100644
--- a/src/libcamera/camera_sensor.cpp
+++ b/src/libcamera/camera_sensor.cpp
@@ -9,10 +9,12 @@
 
 #include <algorithm>
 #include <float.h>
+#include <fstream>
 #include <iomanip>
 #include <limits.h>
 #include <math.h>
 #include <regex>
+#include <sys/stat.h>
 
 #include <libcamera/property_ids.h>
 
@@ -204,6 +206,11 @@ int CameraSensor::init()
 	if (ret < 0)
 		return ret;
 
+	/* Generate a unique ID for the sensor. */
+	ret = generateID();
+	if (ret)
+		return ret;
+
 	/* Retrieve and store the camera sensor properties. */
 	const ControlInfoMap &controls = subdev_->controls();
 	int32_t propertyValue;
@@ -283,6 +290,17 @@ int CameraSensor::init()
  * \return The sensor model name
  */
 
+/**
+ * \fn CameraSensor::id()
+ * \brief Retrieve the sensor ID
+ *
+ * The sensor ID is a free-formed string that uniquely identifies the sensor in
+ * the system. The ID is persisted between different instances of libcamera and
+ * between resets of the system.
+ *
+ * \return The sensor ID
+ */
+
 /**
  * \fn CameraSensor::entity()
  * \brief Retrieve the sensor media entity
@@ -541,4 +559,71 @@ std::string CameraSensor::logPrefix() const
 	return "'" + entity_->name() + "'";
 }
 
+int CameraSensor::generateID()
+{
+	std::string path, devPath = subdev_->devicePath();
+	struct stat statbuf;
+
+	/* Try to generate ID from OF device tree path.  */
+	path = devPath + "/of_node";
+	if (stat(path.c_str(), &statbuf) == 0) {
+		char ofPath[PATH_MAX];
+
+		if (!realpath(path.c_str(), ofPath)) {
+			LOG(CameraSensor, Error) << "Failed to read sensor OF based ID";
+			return -EINVAL;
+		}
+
+		id_ = ofPath;
+		const std::string dropStr = "/sys/firmware/devicetree/";
+		if (id_.find(dropStr) == 0)
+			id_.erase(0, dropStr.length());
+
+		return 0;
+	}
+
+	/* Try to generate ID from ACPI path. */
+	path = devPath + "/firmware_node/path";
+	if (stat(path.c_str(), &statbuf) == 0) {
+		std::ifstream file(path.c_str());
+
+		if (!file.is_open()) {
+			LOG(CameraSensor, Error) << "Failed to read sensor ACPI based ID";
+			return -EINVAL;
+		}
+
+		std::getline(file, id_);
+		file.close();
+
+		return 0;
+	}
+
+	/*
+	 * VIMC is a virtual video pipeline not backed hardware and have no OF
+	 * or ACPI firmware nodes. Handle this pipeline as a special case and
+	 * generate IDs based on the sensor model.
+	 */
+	path = devPath + "/modalias";
+	if (stat(path.c_str(), &statbuf) == 0) {
+		std::ifstream file(path.c_str());
+
+		if (!file.is_open()) {
+			LOG(CameraSensor, Error) << "Failed to read sensor ACPI based ID";
+			return -EINVAL;
+		}
+
+		std::string modalias;
+		std::getline(file, modalias);
+		file.close();
+
+		if (modalias == "platform:vimc") {
+			id_ = "VIMC " + model();
+			return 0;
+		}
+	}
+
+	LOG(CameraSensor, Error) << "Unknown sensor device type, can not generate ID";
+	return -EINVAL;
+}
+
 } /* namespace libcamera */
-- 
2.27.0