[libcamera-devel] [PATCH v2 1/2] pipeline: raspberrypi: Fix under-allocation of embedded data buffers

[David Plowman]

The code was reducing the number of raw stream buffers allocated when
the application is providing some of its own. However, it was not
taking account of the fact that the application cannot supply embedded
data buffers, so it must always allocate a reasonable minimum number
of these buffers (possibly more than the number of raw stream buffers)
to prevent frame drops.

Signed-off-by: David Plowman <david.plowman at raspberrypi.com>
Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
Reviewed-by: Naushir Patuck <naush at raspberrypi.com>
---
 .../pipeline/raspberrypi/raspberrypi.cpp      | 25 ++++++++++++-------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
index e31fa3b2..045725dd 100644
--- a/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
+++ b/src/libcamera/pipeline/raspberrypi/raspberrypi.cpp
@@ -1248,18 +1248,25 @@ int PipelineHandlerRPi::prepareBuffers(Camera *camera)
 	/* Decide how many internal buffers to allocate. */
 	for (auto const stream : data->streams_) {
 		unsigned int numBuffers;
-
-		if (stream == &data->unicam_[Unicam::Image] ||
-		    stream == &data->unicam_[Unicam::Embedded]) {
+		/*
+		 * For Unicam, allocate a minimum of 4 buffers as we want
+		 * to avoid any frame drops.
+		 */
+		constexpr unsigned int minBuffers = 4;
+		if (stream == &data->unicam_[Unicam::Image]) {
 			/*
-			 * For Unicam, allocate a minimum of 4 buffers as we want
-			 * to avoid any frame drops. If an application has configured
-			 * a RAW stream, allocate additional buffers to make up the
-			 * minimum, but ensure we have at least 2 sets of internal
-			 * buffers to use to minimise frame drops.
+			 * If an application has configured a RAW stream, allocate
+			 * additional buffers to make up the minimum, but ensure
+			 * we have at least 2 sets of internal buffers to use to
+			 * minimise frame drops.
 			 */
-			constexpr unsigned int minBuffers = 4;
 			numBuffers = std::max<int>(2, minBuffers - numRawBuffers);
+		} else if (stream == &data->unicam_[Unicam::Embedded]) {
+			/*
+			 * Embedded data buffers are (currently) for internal use,
+			 * so allocate the minimum required to avoid frame drops.
+			 */
+			numBuffers = minBuffers;
 		} else {
 			/*
 			 * Since the ISP runs synchronous with the IPA and requests,
-- 
2.30.2