[libcamera-devel] [PATCH v8 06/17] libcamera: pipeline: rkisp1: Don't rely on bufferCount

[Nícolas F. R. A. Prado]

Currently the rkisp1 pipeline handler relies on bufferCount to decide on
the number of parameter and statistics buffers to allocate internally
and for the number of V4L2 buffer slots to reserve. Instead, the number
of internal buffers should be the minimum required by the pipeline to
keep the requests flowing, in order to avoid wasting memory, while the
number of V4L2 buffer slots should be greater than the expected number
of requests queued by the application, in order to avoid thrashing
dmabuf mappings, which would degrade performance.

Stop relying on bufferCount for these numbers and instead set them to
appropriate, and independent, constants.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado at collabora.com>

---

Changes in v8:
- New

 src/libcamera/pipeline/rkisp1/rkisp1.cpp      | 19 ++++++++++++-------
 src/libcamera/pipeline/rkisp1/rkisp1_path.cpp |  3 +--
 src/libcamera/pipeline/rkisp1/rkisp1_path.h   |  2 ++
 3 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/libcamera/pipeline/rkisp1/rkisp1.cpp b/src/libcamera/pipeline/rkisp1/rkisp1.cpp
index 853a0ef42ba3..03a8d1d26e30 100644
--- a/src/libcamera/pipeline/rkisp1/rkisp1.cpp
+++ b/src/libcamera/pipeline/rkisp1/rkisp1.cpp
@@ -188,6 +188,16 @@ private:
 	std::queue<FrameBuffer *> availableStatBuffers_;
 
 	Camera *activeCamera_;
+
+	/*
+	 * This many internal buffers (or rather parameter and statistics buffer
+	 * pairs) ensures that the pipeline runs smoothly, without frame drops.
+	 * This number considers:
+	 * - three buffers queued to the driver, which is also the minimum
+	 *   required to start streaming
+	 * - one buffer being processed on the IPA
+	 */
+	static constexpr unsigned int kRkISP1InternalBufferCount = 4;
 };
 
 RkISP1Frames::RkISP1Frames(PipelineHandler *pipe)
@@ -693,16 +703,11 @@ int PipelineHandlerRkISP1::allocateBuffers(Camera *camera)
 	unsigned int ipaBufferId = 1;
 	int ret;
 
-	unsigned int maxCount = std::max({
-		data->mainPathStream_.configuration().bufferCount,
-		data->selfPathStream_.configuration().bufferCount,
-	});
-
-	ret = param_->allocateBuffers(maxCount, &paramBuffers_);
+	ret = param_->allocateBuffers(kRkISP1InternalBufferCount, &paramBuffers_);
 	if (ret < 0)
 		goto error;
 
-	ret = stat_->allocateBuffers(maxCount, &statBuffers_);
+	ret = stat_->allocateBuffers(kRkISP1InternalBufferCount, &statBuffers_);
 	if (ret < 0)
 		goto error;
 
diff --git a/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp b/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
index 25f482eb8d8e..515f4be16d7e 100644
--- a/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
+++ b/src/libcamera/pipeline/rkisp1/rkisp1_path.cpp
@@ -171,8 +171,7 @@ int RkISP1Path::start()
 	if (running_)
 		return -EBUSY;
 
-	/* \todo Make buffer count user configurable. */
-	ret = video_->importBuffers(RKISP1_BUFFER_COUNT);
+	ret = video_->importBuffers(kRkISP1BufferSlotCount);
 	if (ret)
 		return ret;
 
diff --git a/src/libcamera/pipeline/rkisp1/rkisp1_path.h b/src/libcamera/pipeline/rkisp1/rkisp1_path.h
index 91757600ccdc..267d8f988ace 100644
--- a/src/libcamera/pipeline/rkisp1/rkisp1_path.h
+++ b/src/libcamera/pipeline/rkisp1/rkisp1_path.h
@@ -69,6 +69,8 @@ private:
 	std::unique_ptr<V4L2Subdevice> resizer_;
 	std::unique_ptr<V4L2VideoDevice> video_;
 	MediaLink *link_;
+
+	static constexpr unsigned int kRkISP1BufferSlotCount = 16;
 };
 
 class RkISP1MainPath : public RkISP1Path
-- 
2.33.0