[libcamera-devel] [PATCH v8 07/17] libcamera: pipeline: vimc, uvcvideo: Don't rely on bufferCount

[Nícolas F. R. A. Prado]

Instead of using bufferCount as the number of V4L2 buffer slots to
reserve in the vimc and uvcvideo pipeline handlers, use a reasonably
high constant: 16. Overallocating isn't a problem as buffer slots are
cheap. Having too few, on the other hand, could degrade performance. It
is expected that this number will be more than enough for most, if not
all, use cases.

This makes way for removing bufferCount.

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

---

Changes in v8:
- New

 src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 5 +++--
 src/libcamera/pipeline/vimc/vimc.cpp         | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
index 7821cacfa883..c210cf57750f 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -91,6 +91,8 @@ private:
 	{
 		return static_cast<UVCCameraData *>(camera->_d());
 	}
+
+	static constexpr unsigned int kUVCBufferSlotCount = 16;
 };
 
 UVCCameraConfiguration::UVCCameraConfiguration(UVCCameraData *data)
@@ -236,9 +238,8 @@ int PipelineHandlerUVC::exportFrameBuffers(Camera *camera,
 int PipelineHandlerUVC::start(Camera *camera, [[maybe_unused]] const ControlList *controls)
 {
 	UVCCameraData *data = cameraData(camera);
-	unsigned int count = data->stream_.configuration().bufferCount;
 
-	int ret = data->video_->importBuffers(count);
+	int ret = data->video_->importBuffers(kUVCBufferSlotCount);
 	if (ret < 0)
 		return ret;
 
diff --git a/src/libcamera/pipeline/vimc/vimc.cpp b/src/libcamera/pipeline/vimc/vimc.cpp
index eebdfd1a4c01..d2943f61a745 100644
--- a/src/libcamera/pipeline/vimc/vimc.cpp
+++ b/src/libcamera/pipeline/vimc/vimc.cpp
@@ -105,6 +105,8 @@ private:
 	{
 		return static_cast<VimcCameraData *>(camera->_d());
 	}
+
+	static constexpr unsigned int kVimcBufferSlotCount = 16;
 };
 
 namespace {
@@ -331,9 +333,8 @@ int PipelineHandlerVimc::exportFrameBuffers(Camera *camera,
 int PipelineHandlerVimc::start(Camera *camera, [[maybe_unused]] const ControlList *controls)
 {
 	VimcCameraData *data = cameraData(camera);
-	unsigned int count = data->stream_.configuration().bufferCount;
 
-	int ret = data->video_->importBuffers(count);
+	int ret = data->video_->importBuffers(kVimcBufferSlotCount);
 	if (ret < 0)
 		return ret;
 
-- 
2.33.0