[libcamera-devel] [PATCH v2 09/27] libcamera: framebuffer: Add a function to check if planes are contiguous

[Laurent Pinchart]

Hi Jean-Michel,

On Mon, Sep 06, 2021 at 07:50:58AM +0200, Jean-Michel Hautbois wrote:
> On 06/09/2021 04:00, Laurent Pinchart wrote:
> > 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 at ideasonboard.com>
> > Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> > Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
> > ---
> > Changes v1:
> > 
> > - Merge both loops in FrameBuffer::FrameBuffer()
> > ---
> >  include/libcamera/internal/framebuffer.h |  2 ++
> >  src/libcamera/framebuffer.cpp            | 45 ++++++++++++++++++++++--
> >  2 files changed, 45 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/framebuffer.h b/include/libcamera/internal/framebuffer.h
> > index 606aed2b4782..cd33c295466e 100644
> > --- a/include/libcamera/internal/framebuffer.h
> > +++ b/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 */
> > diff --git a/src/libcamera/framebuffer.cpp b/src/libcamera/framebuffer.cpp
> > index ad63a34a83bf..e71c2ffae034 100644
> > --- a/src/libcamera/framebuffer.cpp
> > +++ b/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.
> > +		 */
> 
> How is that possible ?

dup(), or IPC. Depending on the IPC mechanism, if you send the same fd
twice (once for each plane in an NV12 buffer for instance), you may get
two different fds on the receiving side.

> > +		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;
> >  }
> >  
> >  /**

-- 
Regards,

Laurent Pinchart