[libcamera-devel] [PATCH/RFC] libcamera: pipeline: simple: Support camera sensors that contain an ISP

[Laurent Pinchart]

Camera sensors can include an ISP. For instance, the AP1302 external ISP
can be connected to up to two raw camera sensors, and the combination of
the sensors and ISP is considered as a (smart) camera sensor from
libcamera's point of view.

The CameraSensor class has limited support for this already. Extend the
simple pipeline handler to support such sensors, by using the media
entity corresponding to the ISP instead of the raw camera sensor's
entity.

We don't need to handle the case where an entity in the SoC would expose
the MEDIA_ENT_F_PROC_VIDEO_ISP function, as pipeline containing an ISP
would have a dedicated pipeline handler.

The implementation is limited as it won't support other multi-entity
camera sensors (such as CCS). While this would be worth supporting, we
don't have a test platform with a CCS-compatible sensor at this point,
so let's not over-engineer the solution. Extending support to CCS (and
possibly other sensor topologies) will likely involve helpers that can
be used by other pipeline handlers (such as generic graph walk helpers
for instance) and extensions to the CameraSensor class.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/libcamera/pipeline/simple/simple.cpp | 87 ++++++++++++++++++++----
 1 file changed, 74 insertions(+), 13 deletions(-)

This patch depends on "[PATCH/RFC] libcamera: camera_sensor: Accept
entities exposing the ISP function" ([1]). It has been tested on a
MediaTek Pumpkin i500 board with an ON Semiconductor AP1302 and AR0330
and AR0144 sensors.

[1] https://patchwork.libcamera.org/patch/11182/

diff --git a/src/libcamera/pipeline/simple/simple.cpp b/src/libcamera/pipeline/simple/simple.cpp
index 9d468f7c9cc4..2df33a3a79ea 100644
--- a/src/libcamera/pipeline/simple/simple.cpp
+++ b/src/libcamera/pipeline/simple/simple.cpp
@@ -240,6 +240,8 @@ private:
 			PipelineHandler::cameraData(camera));
 	}
 
+	std::vector<MediaEntity *> locateSensors();
+
 	void bufferReady(FrameBuffer *buffer);
 	void converterInputDone(FrameBuffer *buffer);
 	void converterOutputDone(FrameBuffer *buffer);
@@ -865,6 +867,77 @@ int SimplePipelineHandler::queueRequestDevice(Camera *camera, Request *request)
  * Match and Setup
  */
 
+std::vector<MediaEntity *> SimplePipelineHandler::locateSensors()
+{
+	std::vector<MediaEntity *> entities;
+
+	/*
+	 * Gather all the camera sensor entities based on the function they
+	 * expose.
+	 */
+	for (MediaEntity *entity : media_->entities()) {
+		if (entity->function() == MEDIA_ENT_F_CAM_SENSOR)
+			entities.push_back(entity);
+	}
+
+	if (entities.empty())
+		return {};
+
+	/*
+	 * Sensors can be made of multiple entities. For instance, a raw sensor
+	 * can be connected to an ISP, and the combination of both should be
+	 * treated as one sensor. To support this, as a crude heuristic, check
+	 * the downstream entity from the camera sensor, and if it is an ISP,
+	 * use it instead of the sensor.
+	 */
+	std::vector<MediaEntity *> sensors;
+
+	for (MediaEntity *entity : entities) {
+		/*
+		 * Locate the downstream entity by following the first enabled
+		 * link from a source pad.
+		 */
+		const MediaPad *pad = nullptr;
+		const MediaLink *link = nullptr;
+
+		for (const MediaPad *p : entity->pads()) {
+			if (p->flags() & MEDIA_PAD_FL_SOURCE) {
+				pad = p;
+				break;
+			}
+		}
+
+		if (!pad)
+			continue;
+
+		for (const MediaLink *l : pad->links()) {
+			if (l->flags() & MEDIA_LNK_FL_ENABLED) {
+				link = l;
+				break;
+			}
+		}
+
+		if (!link)
+			continue;
+
+		MediaEntity *remote = link->sink()->entity();
+		if (remote->function() == MEDIA_ENT_F_PROC_VIDEO_ISP)
+			sensors.push_back(remote);
+		else
+			sensors.push_back(entity);
+	}
+
+	/*
+	 * Remove duplicates, in case multiple sensors are connected to the
+	 * same ISP.
+	 */
+	std::sort(sensors.begin(), sensors.end());
+	auto last = std::unique(sensors.begin(), sensors.end());
+	sensors.erase(last, sensors.end());
+
+	return sensors;
+}
+
 bool SimplePipelineHandler::match(DeviceEnumerator *enumerator)
 {
 	const SimplePipelineInfo *info = nullptr;
@@ -888,19 +961,7 @@ bool SimplePipelineHandler::match(DeviceEnumerator *enumerator)
 	}
 
 	/* Locate the sensors. */
-	std::vector<MediaEntity *> sensors;
-
-	for (MediaEntity *entity : media_->entities()) {
-		switch (entity->function()) {
-		case MEDIA_ENT_F_CAM_SENSOR:
-			sensors.push_back(entity);
-			break;
-
-		default:
-			break;
-		}
-	}
-
+	std::vector<MediaEntity *> sensors = locateSensors();
 	if (sensors.empty()) {
 		LOG(SimplePipeline, Error) << "No sensor found";
 		return false;
-- 
Regards,

Laurent Pinchart