[libcamera-devel] [RFC PATCH v2 01/10] libcamera: framebuffer: Add offset to FrameBuffer::Plane

[Laurent Pinchart]

Hi Hiro,

Thank you for the patch.

On Mon, Aug 23, 2021 at 10:12:12PM +0900, Hirokazu Honda wrote:
> This adds offset to FrameBuffer::Plane. It enables representing frame
> buffers that store planes in the same dmabuf at different offsets, as
> for instance required by the V4L2 NV12 pixel format.
> 
> Signed-off-by: Hirokazu Honda <hiroh at chromium.org>
> Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> ---
>  include/libcamera/framebuffer.h          |  1 +
>  src/android/mm/generic_camera_buffer.cpp |  2 --
>  src/libcamera/framebuffer.cpp            | 27 ++++++++++++++----------
>  3 files changed, 17 insertions(+), 13 deletions(-)
> 
> diff --git a/include/libcamera/framebuffer.h b/include/libcamera/framebuffer.h
> index 28307890..5de3c744 100644
> --- a/include/libcamera/framebuffer.h
> +++ b/include/libcamera/framebuffer.h
> @@ -42,6 +42,7 @@ class FrameBuffer final : public Extensible
>  public:
>  	struct Plane {
>  		FileDescriptor fd;
> +		unsigned int offset;
>  		unsigned int length;
>  	};
>  
> diff --git a/src/android/mm/generic_camera_buffer.cpp b/src/android/mm/generic_camera_buffer.cpp
> index b296b3e3..73fbd97a 100644
> --- a/src/android/mm/generic_camera_buffer.cpp
> +++ b/src/android/mm/generic_camera_buffer.cpp
> @@ -52,8 +52,6 @@ private:
>  	int fd_;
>  	int flags_;
>  	std::vector<PlaneInfo> planeInfo_;
> -	/* \todo remove planes_ is added to MappedBuffer. */
> -	std::vector<Span<uint8_t>> planes_;

This breaks compilation, as the planes_ member is added to MappedBuffer
in "libcamera: mapped_framebuffer: Return plane begin address by
MappedBuffer::maps()".

>  };
>  
>  CameraBuffer::Private::Private([[maybe_unused]] CameraBuffer *cameraBuffer,
> diff --git a/src/libcamera/framebuffer.cpp b/src/libcamera/framebuffer.cpp
> index b401c50e..e9467aa0 100644
> --- a/src/libcamera/framebuffer.cpp
> +++ b/src/libcamera/framebuffer.cpp
> @@ -131,7 +131,7 @@ FrameBuffer::Private::Private()
>   *
>   * The static information describes the memory planes that make a frame. The
>   * planes are specified when creating the FrameBuffer and are expressed as a set
> - * of dmabuf file descriptors and length.
> + * of dmabuf file descriptors, offset and length.
>   *
>   * The dynamic information is grouped in a FrameMetadata instance. It is updated
>   * during the processing of a queued capture request, and is valid from the
> @@ -151,18 +151,18 @@ FrameBuffer::Private::Private()
>   *
>   * Planar pixel formats use multiple memory regions to store the different
>   * colour components of a frame. The Plane structure describes such a memory
> - * region by a dmabuf file descriptor and a length. A FrameBuffer then
> - * contains one or multiple planes, depending on the pixel format of the
> - * frames it is meant to store.
> + * region by a dmabuf file descriptor, an offset within the dmabuf and a length.
> + * A FrameBuffer then contains one or multiple planes, depending on the pixel
> + * format of the frames it is meant to store.
>   *
> - * To support DMA access, planes are associated with dmabuf objects represented
> - * by FileDescriptor handles. The Plane class doesn't handle mapping of the
> - * memory to the CPU, but applications and IPAs may use the dmabuf file
> - * descriptors to map the plane memory with mmap() and access its contents.

I think this paragraph should be kept, it's still valid.

> + * The offset identifies the location of the plane data from the start of the
> + * memory referenced by the dmabuf file descriptor. Multiple planes may be
> + * stored in the same dmabuf, in which case they will reference the same dmabuf
> + * and different offsets. No two planes may overlap, as specified by their
> + * offset and length.
>   *
> - * \todo Once we have a Kernel API which can express offsets within a plane
> - * this structure shall be extended to contain this information. See commit
> - * 83148ce8be55e for initial documentation of this feature.
> + * \todo Specify how an application shall decide whether to use a single or
> + * multiple dmabufs, based on the camera requirements.
>   */
>  
>  /**
> @@ -170,6 +170,11 @@ FrameBuffer::Private::Private()
>   * \brief The dmabuf file descriptor
>   */
>  
> +/**
> + * \var FrameBuffer::Plane::offset
> + * \brief The plane offset in bytes
> +*/
> +
>  /**
>   * \var FrameBuffer::Plane::length
>   * \brief The plane length in bytes

-- 
Regards,

Laurent Pinchart