From d9d265cfce1f76d5df27719b7820440fc4f9638c Mon Sep 17 00:00:00 2001
From: Naushir Patuck <naush@raspberrypi.com>
Date: Thu, 18 Dec 2025 12:31:24 +0000
Subject: [PATCH] pipeline: rpi: Rework internal buffer allocations
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In order to clear the V4L2VideoDevice cache, we must call
V4L2VideoDevice::releaseBuffers() when stopping the camera. To do this
without releasing the allocated buffers, we have to rework the internal
buffer allocation logic.

Remove calls to V4L2VideoDevice::importBuffers() and releaseBuffers()
from within the RPi::Stream class. Instead, move these calls to the
PipelineHandlerBase class, where we can call releaseBuffers(), i.e. clear
the V4L2VideoDevice cache unconditionally on stop without de-allocating
the internal buffers.

The code in Stream::clearBuffers() can be then moved into releaseBuffers()
which will actually de-allocate the internal buffers when required.

Closes: https://gitlab.freedesktop.org/camera/libcamera/-/issues/265
Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Tested-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com> # rpi4
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
---
 .../pipeline/rpi/common/pipeline_base.cpp     |  8 ++++++-
 .../pipeline/rpi/common/rpi_stream.cpp        | 23 ++++++-------------
 .../pipeline/rpi/common/rpi_stream.h          |  1 -
 3 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/src/libcamera/pipeline/rpi/common/pipeline_base.cpp b/src/libcamera/pipeline/rpi/common/pipeline_base.cpp
index 8784c229..fb8e466f 100644
--- a/src/libcamera/pipeline/rpi/common/pipeline_base.cpp
+++ b/src/libcamera/pipeline/rpi/common/pipeline_base.cpp
@@ -719,8 +719,10 @@ void PipelineHandlerBase::stopDevice(Camera *camera)
 	data->state_ = CameraData::State::Stopped;
 	data->platformStop();
 
-	for (auto const stream : data->streams_)
+	for (auto const stream : data->streams_) {
 		stream->dev()->streamOff();
+		stream->dev()->releaseBuffers();
+	}
 
 	/* Disable SOF event generation. */
 	data->frontendDevice()->setFrameStartEnabled(false);
@@ -901,6 +903,10 @@ int PipelineHandlerBase::queueAllBuffers(Camera *camera)
 	int ret;
 
 	for (auto const stream : data->streams_) {
+		ret = stream->dev()->importBuffers(VIDEO_MAX_FRAME);
+		if (ret < 0)
+			return ret;
+
 		if (stream->getFlags() & StreamFlag::External)
 			continue;
 
diff --git a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
index e73f4b7d..f420400d 100644
--- a/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
+++ b/src/libcamera/pipeline/rpi/common/rpi_stream.cpp
@@ -12,9 +12,6 @@
 
 #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)
@@ -108,7 +105,7 @@ void Stream::setExportedBuffer(FrameBuffer *buffer)
 
 int Stream::allocateBuffers(unsigned int count)
 {
-	int ret;
+	int ret = 0;
 
 	if (!(flags_ & StreamFlag::ImportOnly)) {
 		/* Export some frame buffers for internal use. */
@@ -121,7 +118,7 @@ int Stream::allocateBuffers(unsigned int count)
 		resetBuffers();
 	}
 
-	return dev_->importBuffers(maxV4L2BufferCount);
+	return ret;
 }
 
 int Stream::queueBuffer(FrameBuffer *buffer)
@@ -243,8 +240,11 @@ int Stream::queueAllBuffers()
 
 void Stream::releaseBuffers()
 {
-	dev_->releaseBuffers();
-	clearBuffers();
+	availableBuffers_ = std::queue<FrameBuffer *>{};
+	requestBuffers_ = std::queue<FrameBuffer *>{};
+	internalBuffers_.clear();
+	bufferMap_.clear();
+	id_ = 0;
 }
 
 void Stream::bufferEmplace(unsigned int id, FrameBuffer *buffer)
@@ -257,15 +257,6 @@ void Stream::bufferEmplace(unsigned int id, FrameBuffer *buffer)
 				   std::forward_as_tuple(buffer, false));
 }
 
-void Stream::clearBuffers()
-{
-	availableBuffers_ = std::queue<FrameBuffer *>{};
-	requestBuffers_ = std::queue<FrameBuffer *>{};
-	internalBuffers_.clear();
-	bufferMap_.clear();
-	id_ = 0;
-}
-
 int Stream::queueToDevice(FrameBuffer *buffer)
 {
 	LOG(RPISTREAM, Debug) << "Queuing buffer " << getBufferId(buffer)
diff --git a/src/libcamera/pipeline/rpi/common/rpi_stream.h b/src/libcamera/pipeline/rpi/common/rpi_stream.h
index c267447e..300a352a 100644
--- a/src/libcamera/pipeline/rpi/common/rpi_stream.h
+++ b/src/libcamera/pipeline/rpi/common/rpi_stream.h
@@ -140,7 +140,6 @@ public:
 
 private:
 	void bufferEmplace(unsigned int id, FrameBuffer *buffer);
-	void clearBuffers();
 	int queueToDevice(FrameBuffer *buffer);
 
 	StreamFlags flags_;