[libcamera-devel] [PATCH v1 2/2] pipeline: raspberrypi: Fix the buffer count calculation for the ISP input stream

[Naushir Patuck]

The ISP input stream currently only allocates a single slot in the
V4L2VideoDevice cache as it follows the number of buffers allocated for use.
However, this is wrong as the ISP input stream imports buffers from Unicam
image stream.  As a consequence of this, only one cache slot was used during
runtime for the ISP input stream, and if multiple buffers were to be queued
simultaneously, the queue operation would return a failure.

Fix this by passing the same number of RAW buffers available from the Unicam
image stream. Additionally, double this count in the cases where buffers could
be allocated externally from the application.

Bug: https://github.com/raspberrypi/libcamera-apps/issues/236
     https://github.com/raspberrypi/libcamera-apps/issues/238
     https://github.com/raspberrypi/libcamera-apps/issues/240
Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
---
 src/libcamera/pipeline/raspberrypi/raspberrypi.cpp | 8 ++++++++
 src/libcamera/pipeline/raspberrypi/rpi_stream.cpp  | 3 ++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
index 6a46e6bc89fa..49af56edc1f9 100644
--- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
+++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
@@ -1382,6 +1382,14 @@ int PipelineHandlerRPi::prepareBuffers(Camera *camera)
 			 * minimise frame drops.
 			 */
 			numBuffers = std::max<int>(2, minBuffers - numRawBuffers);
+		} else if (stream == &data->isp_[Isp::Input]) {
+			/*
+			 * ISP input buffers are imported from Unicam, so follow
+			 * similar logic as above to count all the RAW buffers
+			 * available.
+			 */
+			numBuffers = numRawBuffers + std::max<int>(2, minBuffers - numRawBuffers);
+
 		} else if (stream == &data->unicam_[Unicam::Embedded]) {
 			/*
 			 * Embedded data buffers are (currently) for internal use,
diff --git a/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp b/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
index a4159e20b068..a421ad09ba50 100644
--- a/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
+++ b/src/libcamera/pipeline/raspberrypi/rpi_stream.cpp
@@ -111,11 +111,12 @@ int Stream::prepareBuffers(unsigned int count)
 	 * 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 (isExternal())
+	if (isExternal() || importOnly_)
 		count = count * 2;
 
 	return dev_->importBuffers(count);
-- 
2.25.1