[libcamera-devel] [PATCH v10 08/19] libcamera: pipeline: vimc, uvcvideo: Don't rely on bufferCount

[Paul Elder]

From: Nícolas F. R. A. Prado <nfraprado at collabora.com>

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>
Reviewed-by: Paul Elder <paul.elder at ideasonboard.com>
Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo at jmondi.org>

---
Changes in v9:
- rebased

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 4ce240a4..18966d01 100644
--- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
+++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
@@ -97,6 +97,8 @@ private:
 	{
 		return static_cast<UVCCameraData *>(camera->_d());
 	}
+
+	static constexpr unsigned int kUVCBufferSlotCount = 16;
 };
 
 UVCCameraConfiguration::UVCCameraConfiguration(UVCCameraData *data)
@@ -239,9 +241,8 @@ 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 e58caf99..eaa6ebf7 100644
--- a/src/libcamera/pipeline/vimc/vimc.cpp
+++ b/src/libcamera/pipeline/vimc/vimc.cpp
@@ -106,6 +106,8 @@ private:
 	{
 		return static_cast<VimcCameraData *>(camera->_d());
 	}
+
+	static constexpr unsigned int kVimcBufferSlotCount = 16;
 };
 
 namespace {
@@ -334,9 +336,8 @@ 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;
 
-- 
2.35.1