libcamera: framebuffer: Add a function to check if planes are contiguous

Multi-planar frame buffers can store their planes contiguously in
memory, or split them in discontiguous memory areas. Add a private
function to check in which of these two categories the frame buffer
belongs. This will be used to correctly handle the differences between
the V4L2 single and multi planar APIs.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>

include/libcamera/internal/framebuffer.h

@@ -21,9 +21,11 @@ public:
 	Private();
 
 	void setRequest(Request *request) { request_ = request; }
+	bool isContiguous() const { return isContiguous_; }
 
 private:
 	Request *request_;
+	bool isContiguous_;
 };
 
 } /* namespace libcamera */

src/libcamera/framebuffer.cpp

@@ -106,7 +106,7 @@ LOG_DEFINE_CATEGORY(Buffer)
  */
 
 FrameBuffer::Private::Private()
-	: request_(nullptr)
+	: request_(nullptr), isContiguous_(true)
 {
 }
 
@@ -120,6 +120,17 @@ FrameBuffer::Private::Private()
  * handlers, it is called by the pipeline handlers themselves.
  */
 
+/**
+ * \fn FrameBuffer::Private::isContiguous()
+ * \brief Check if the frame buffer stores planes contiguously in memory
+ *
+ * Multi-planar frame buffers can store their planes contiguously in memory, or
+ * split them into discontiguous memory areas. This function checks in which of
+ * these two categories the frame buffer belongs.
+ *
+ * \return True if the planes are stored contiguously in memory, false otherwise
+ */
+
 /**
  * \class FrameBuffer
  * \brief Frame buffer data and its associated dynamic metadata
@@ -199,8 +210,38 @@ FrameBuffer::FrameBuffer(const std::vector<Plane> &planes, unsigned int cookie)
 	: Extensible(std::make_unique<Private>()), planes_(planes),
 	  cookie_(cookie)
 {
-	for (const auto &plane : planes_)
+	unsigned int offset = 0;
+	bool isContiguous = true;
+	ino_t inode = 0;
+
+	for (const auto &plane : planes_) {
 		ASSERT(plane.offset != Plane::kInvalidOffset);
+
+		if (plane.offset != offset) {
+			isContiguous = false;
+			break;
+		}
+
+		/*
+		 * Two different dmabuf file descriptors may still refer to the
+		 * same dmabuf instance. Check this using inodes.
+		 */
+		if (plane.fd.fd() != planes_[0].fd.fd()) {
+			if (!inode)
+				inode = planes_[0].fd.inode();
+			if (plane.fd.inode() != inode) {
+				isContiguous = false;
+				break;
+			}
+		}
+
+		offset += plane.length;
+	}
+
+	LOG(Buffer, Debug)
+		<< "Buffer is " << (isContiguous ? "not " : "") << "contiguous";
+
+	_d()->isContiguous_ = isContiguous;
 }
 
 /**