[libcamera-devel] [PATCH 06/10] libcamera: framebuffer: Add synchronization Fence

[Jacopo Mondi]

Add an optional synchronization file descriptor to the FrameBuffer constuctor.

The fence is handled by the FrameBuffer::Private class by constructing
a Fence class instance to wrap the file descriptor. Once the Request the
FrameBuffer is part of has completed, the fence file descriptor will read
as -1 if successfully handled by the library; otherwise the file
descriptor value is kept and applications are responsible for closing
it.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 include/libcamera/framebuffer.h          |  5 ++-
 include/libcamera/internal/framebuffer.h |  7 +++-
 src/libcamera/framebuffer.cpp            | 46 +++++++++++++++++++++---
 3 files changed, 52 insertions(+), 6 deletions(-)

diff --git a/include/libcamera/framebuffer.h b/include/libcamera/framebuffer.h
index 7f2f176af691..ac96790b76c0 100644
--- a/include/libcamera/framebuffer.h
+++ b/include/libcamera/framebuffer.h
@@ -57,7 +57,8 @@ public:
 		unsigned int length;
 	};
 
-	FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie = 0);
+	FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie = 0,
+		    int fence = -1);
 
 	const std::vector<Plane> &planes() const { return planes_; }
 	Request *request() const;
@@ -66,6 +67,8 @@ public:
 	unsigned int cookie() const { return cookie_; }
 	void setCookie(unsigned int cookie) { cookie_ = cookie; }
 
+	int fence() const;
+
 	void cancel() { metadata_.status = FrameMetadata::FrameCancelled; }
 
 private:
diff --git a/include/libcamera/internal/framebuffer.h b/include/libcamera/internal/framebuffer.h
index cd33c295466e..db1a4bd72354 100644
--- a/include/libcamera/internal/framebuffer.h
+++ b/include/libcamera/internal/framebuffer.h
@@ -11,6 +11,8 @@
 
 #include <libcamera/framebuffer.h>
 
+#include <libcamera/internal/fence.h>
+
 namespace libcamera {
 
 class FrameBuffer::Private : public Extensible::Private
@@ -18,14 +20,17 @@ class FrameBuffer::Private : public Extensible::Private
 	LIBCAMERA_DECLARE_PUBLIC(FrameBuffer)
 
 public:
-	Private();
+	Private(int fence);
 
 	void setRequest(Request *request) { request_ = request; }
 	bool isContiguous() const { return isContiguous_; }
+	const Fence &fence() const { return fence_; }
+	Fence &fence() { return fence_; }
 
 private:
 	Request *request_;
 	bool isContiguous_;
+	Fence fence_;
 };
 
 } /* namespace libcamera */
diff --git a/src/libcamera/framebuffer.cpp b/src/libcamera/framebuffer.cpp
index d44a98babd05..c3e03896b184 100644
--- a/src/libcamera/framebuffer.cpp
+++ b/src/libcamera/framebuffer.cpp
@@ -111,8 +111,12 @@ LOG_DEFINE_CATEGORY(Buffer)
  * pipeline handlers.
  */
 
-FrameBuffer::Private::Private()
-	: request_(nullptr), isContiguous_(true)
+/**
+ * \brief Construct a FrameBuffer::Private instance
+ * \param[in] fence The synchronization fence file descriptor
+ */
+FrameBuffer::Private::Private(int fence)
+	: request_(nullptr), isContiguous_(true), fence_(fence)
 {
 }
 
@@ -137,6 +141,18 @@ FrameBuffer::Private::Private()
  * \return True if the planes are stored contiguously in memory, false otherwise
  */
 
+/**
+ * \fn const FrameBuffer::Private::fence() const
+ * \brief Return a const reference to the Fence
+ * \return A const reference to the frame buffer fence
+ */
+
+/**
+ * \fn FrameBuffer::Private::fence()
+ * \brief Return a reference to the Fence
+ * \return A reference to the frame buffer fence
+ */
+
 /**
  * \class FrameBuffer
  * \brief Frame buffer data and its associated dynamic metadata
@@ -211,9 +227,11 @@ FrameBuffer::Private::Private()
  * \brief Construct a FrameBuffer with an array of planes
  * \param[in] planes The frame memory planes
  * \param[in] cookie Cookie
+ * \param[in] fence Synchronization fence
  */
-FrameBuffer::FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie)
-	: Extensible(std::make_unique<Private>()), planes_(planes),
+FrameBuffer::FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie,
+			 int fence)
+	: Extensible(std::make_unique<Private>(fence)), planes_(planes),
 	  cookie_(cookie)
 {
 	metadata_.planes_.resize(planes_.size());
@@ -305,6 +323,26 @@ Request *FrameBuffer::request() const
  * libcamera core never modifies the buffer cookie.
  */
 
+/**
+ * \fn FrameBuffer::fence()
+ * \brief Return the synchronization fence file descriptor
+ *
+ * The fence file descriptor is set by applications at construction time.
+ *
+ * Once the Request is queued to the Camera the fence is handled by the
+ * library and if successfully notified the fence will read as -1 after the
+ * Request has completed.
+ *
+ * If waiting for fence fails, the fence is instead kept in the FrameBuffer
+ * after the Request has completed and it is responsibility of the
+ * application to correctly close it.
+ */
+int FrameBuffer::fence() const
+{
+	const Fence &fence = _d()->fence();
+	return fence.fd();
+}
+
 /**
  * \fn FrameBuffer::cancel()
  * \brief Marks the buffer as cancelled
-- 
2.33.1