pipeline: rpi: Increase buffer import count to 32

Hardcode the maximum number of buffers imported to the V4L2 video device
to 32. This only has a minor disadvantage of over-allocating cache slots
and V4L2 buffer indexes, but does allow more headroom for using dma
buffers allocated from outside of libcamera.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 11 insertions, 25 deletions

diff --git a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
index c158843c..4b20ac3f 100644
--- a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
+++ b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
@@ -8,6 +8,9 @@
 
 #include <libcamera/base/log.h>
 
+/* Maximum number of buffer slots to allocate in the V4L2 device driver. */
+static constexpr unsigned int maxV4L2BufferCount = 32;
+
 namespace libcamera {
 
 LOG_DEFINE_CATEGORY(RPISTREAM)
@@ -95,34 +98,17 @@ int Stream::prepareBuffers(unsigned int count)
 	int ret;
 
 	if (!(flags_ & StreamFlag::ImportOnly)) {
-		if (count) {
-			/* Export some frame buffers for internal use. */
-			ret = dev_->exportBuffers(count, &internalBuffers_);
-			if (ret < 0)
-				return ret;
-
-			/* Add these exported buffers to the internal/external buffer list. */
-			setExportedBuffers(&internalBuffers_);
-			resetBuffers();
-		}
+		/* Export some frame buffers for internal use. */
+		ret = dev_->exportBuffers(count, &internalBuffers_);
+		if (ret < 0)
+			return ret;
 
-		/* We must import all internal/external exported buffers. */
-		count = bufferMap_.size();
+		/* Add these exported buffers to the internal/external buffer list. */
+		setExportedBuffers(&internalBuffers_);
+		resetBuffers();
 	}
 
-	/*
-	 * If this is an external stream, we must allocate slots for buffers that
-	 * might be externally allocated. We have no indication of how many buffers
-	 * may be used, so this might overallocate slots in the buffer cache.
-	 * Similarly, if this stream is only importing buffers, we do the same.
-	 *
-	 * \todo Find a better heuristic, or, even better, an exact solution to
-	 * this issue.
-	 */
-	if ((flags_ & StreamFlag::External) || (flags_ & StreamFlag::ImportOnly))
-		count = count * 2;
-
-	return dev_->importBuffers(count);
+	return dev_->importBuffers(maxV4L2BufferCount);
 }
 
 int Stream::queueBuffer(FrameBuffer *buffer)