[libcamera-devel] [PATCH v8 7/9] libcamera: pipeline: uvcvideo: Generate unique camera names

[Niklas Söderlund]

Generate camera names that are unique and persistent between system
resets. The name is constructed from the USB device information as well
as the USB controller on the host.

Before this change example of camera names:

Venus USB2.0 Camera: Venus USB2
Logitech Webcam C930e

After this change the same cameras are:

\_SB_.PCI0.RP05.PXSX-2.1.1:1.0-0ac8:3420
\_SB_.PCI0.RP05.PXSX-2.4:1.0-046d:0843

On OF-based system:

/base/soc/usb at 7e980000/usb-port at 1-1.2:1.0-0ac8:3420

Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
---
* Changes since v7
- Rename function to generateId()
- Improve logic to generate deviceId
- Update format description of USB ID
- Fetch controllerId without using realpath()
- Order the generation of the different parts of the ID to match the
  order in the ID string :-)

* Changes since v5
- New algorithm to generate IDs.

* Changes since v3
- Switch argument to generateName() to UVCCameraData pointer.
---
 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 75 +++++++++++++++++++-
 1 file changed, 74 insertions(+), 1 deletion(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 93e3dc17e3a7105e..9f66844e40cb3cd3 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -6,6 +6,7 @@
  */
 
 #include <algorithm>
+#include <fstream>
 #include <iomanip>
 #include <math.h>
 #include <tuple>
@@ -20,6 +21,7 @@
 #include "libcamera/internal/log.h"
 #include "libcamera/internal/media_device.h"
 #include "libcamera/internal/pipeline_handler.h"
+#include "libcamera/internal/sysfs.h"
 #include "libcamera/internal/utils.h"
 #include "libcamera/internal/v4l2_controls.h"
 #include "libcamera/internal/v4l2_videodevice.h"
@@ -81,6 +83,8 @@ public:
 	bool match(DeviceEnumerator *enumerator) override;
 
 private:
+	std::string generateId(const UVCCameraData *data);
+
 	int processControl(ControlList *controls, unsigned int id,
 			   const ControlValue &value);
 	int processControls(UVCCameraData *data, Request *request);
@@ -379,6 +383,69 @@ int PipelineHandlerUVC::queueRequestDevice(Camera *camera, Request *request)
 	return 0;
 }
 
+std::string PipelineHandlerUVC::generateId(const UVCCameraData *data)
+{
+	const std::string path = data->video_->devicePath();
+
+	/* Create a controller ID from first device described in firmware. */
+	std::string controllerId;
+	std::string searchPath = path;
+	while (true) {
+		std::string::size_type pos = searchPath.rfind('/');
+		if (pos <= 1) {
+			LOG(UVC, Error) << "Can not find controller ID";
+			return {};
+		}
+
+		searchPath = searchPath.substr(0, pos);
+
+		controllerId = sysfs::firmwareNodePath(searchPath);
+		if (!controllerId.empty())
+			break;
+	}
+
+	/*
+	 * Create a USB ID from the device path which has the known format:
+	 *
+	 *	path = bus, "-", ports, ":", config, ".", interface ;
+	 *	bus = number ;
+	 *	ports = port, [ ".", ports ] ;
+	 *	port = number ;
+	 *	config = number ;
+	 *	interface = number ;
+	 *
+	 * Example: 3-2.4:1.0
+	 *
+	 * The bus is not guaranteed to be stable and needs to be stripped from
+	 * the USB ID. The final USB ID is built up of the ports, config and
+	 * interface properties.
+	 *
+	 * Example 2.4:1.0.
+	 */
+	std::string usbId = basename(path.c_str());
+	usbId = usbId.substr(usbId.find('-') + 1);
+
+	/* Creata a device ID from the USB devices vendor and product ID. */
+	std::string deviceId;
+	for (const std::string &name : { "idVendor", "idProduct" }) {
+		std::ifstream file(path + "/../" + name);
+
+		if (!file.is_open())
+			return {};
+
+		std::string value;
+		std::getline(file, value);
+		file.close();
+
+		if (!deviceId.empty())
+			deviceId += ":";
+
+		deviceId += value;
+	}
+
+	return controllerId + "-" + usbId + "-" + deviceId;
+}
+
 bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
 {
 	MediaDevice *media;
@@ -405,8 +472,14 @@ bool PipelineHandlerUVC::match(DeviceEnumerator *enumerator)
 		return false;
 
 	/* Create and register the camera. */
+	std::string id = generateId(data.get());
+	if (id.empty()) {
+		LOG(UVC, Error) << "Failed to generate camera ID";
+		return false;
+	}
+
 	std::set<Stream *> streams{ &data->stream_ };
-	std::shared_ptr<Camera> camera = Camera::create(this, media->model(), streams);
+	std::shared_ptr<Camera> camera = Camera::create(this, id, streams);
 	registerCamera(std::move(camera), std::move(data));
 
 	/* Enable hot-unplug notifications. */
-- 
2.28.0