libcamera: mapped_framebuffer: Return plane begin address by MappedBuffer::maps()

MappedBuffer::maps() returns std::vector<MappedBuffer::Plane>.
Plane has the address, but the address points the beginning of the
buffer containing the plane.
This makes the Plane point the beginning of the plane. So
MappedBuffer::maps()[i].data() returns the address of i-th plane.

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

src/libcamera/v4l2_videodevice.cpp

@@ -1283,6 +1283,12 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
 
 		FrameBuffer::Plane plane;
 		plane.fd = std::move(fd);
+		/*
+		 * V4L2 API doesn't provide dmabuf offset information of plane.
+		 * Set 0 as a placeholder offset.
+		 * \todo Set the right offset once V4L2 API provides a way.
+		 */
+		plane.offset = 0;
 		plane.length = multiPlanar ?
 			buf.m.planes[nplane].length : buf.length;