[libcamera-devel] [RFC PATCH v1 09/12] libcamera: v4l2_videodevice: Cache PixelFormatInfo

[Laurent Pinchart]

Hi Kieran,

On Thu, Sep 02, 2021 at 11:21:29AM +0100, Kieran Bingham wrote:
> On 02/09/2021 05:23, Laurent Pinchart wrote:
> > Cache the PixelFormatInfo instead of looking it up in every call to
> > createBuffer(). This prepare for usage of the info in queueBuffer(), to
> 
> s/prepare/prepares/
> 
> > avoid a looking every time a buffer is queued.
> > 
> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > ---
> >  include/libcamera/internal/v4l2_videodevice.h |  1 +
> >  src/libcamera/v4l2_videodevice.cpp            | 19 +++++++++++--------
> >  2 files changed, 12 insertions(+), 8 deletions(-)
> > 
> > diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
> > index 7a145f608a5b..6096cd609b97 100644
> > --- a/include/libcamera/internal/v4l2_videodevice.h
> > +++ b/include/libcamera/internal/v4l2_videodevice.h
> > @@ -243,6 +243,7 @@ private:
> >  
> >  	V4L2Capability caps_;
> >  	V4L2DeviceFormat format_;
> > +	const PixelFormatInfo *formatInfo_;
> >  
> >  	enum v4l2_buf_type bufferType_;
> >  	enum v4l2_memory memoryType_;
> > diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> > index 82ddaed3656f..2d9a94c3c974 100644
> > --- a/src/libcamera/v4l2_videodevice.cpp
> > +++ b/src/libcamera/v4l2_videodevice.cpp
> > @@ -482,8 +482,8 @@ const std::string V4L2DeviceFormat::toString() const
> >   * \param[in] deviceNode The file-system path to the video device node
> >   */
> >  V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
> > -	: V4L2Device(deviceNode), cache_(nullptr), fdBufferNotifier_(nullptr),
> > -	  streaming_(false)
> > +	: V4L2Device(deviceNode), formatInfo_(nullptr), cache_(nullptr),
> > +	  fdBufferNotifier_(nullptr), streaming_(false)
> >  {
> >  	/*
> >  	 * We default to an MMAP based CAPTURE video device, however this will
> > @@ -586,6 +586,7 @@ int V4L2VideoDevice::open()
> >  		return ret;
> >  	}
> >  
> > +	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);
> 
> I shudder a little seeing code hugging the return like that ;-)
> 
> But it's purely subjective, same below of course.

We have various patterns indeed :-) I haven't been able to establish yet
what my mental process to deal with these are, sometimes it bothers me
too, but not always.

> >  	return 0;
> >  }
> >  
> > @@ -681,6 +682,7 @@ int V4L2VideoDevice::open(int handle, enum v4l2_buf_type type)
> >  		return ret;
> >  	}
> >  
> > +	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);
> >  	return 0;
> >  }
> >  
> > @@ -695,6 +697,8 @@ void V4L2VideoDevice::close()
> >  	releaseBuffers();
> >  	delete fdBufferNotifier_;
> >  
> > +	formatInfo_ = nullptr;
> > +
> >  	V4L2Device::close();
> >  }
> >  
> > @@ -787,6 +791,7 @@ int V4L2VideoDevice::setFormat(V4L2DeviceFormat *format)
> >  		return ret;
> >  
> >  	format_ = *format;
> > +	formatInfo_ = &PixelFormatInfo::info(format_.fourcc);
> 
> Looks like we were already using that pattern though ;-)
> 
> >  	return 0;
> >  }
> >  
> > @@ -1325,19 +1330,17 @@ std::unique_ptr<FrameBuffer> V4L2VideoDevice::createBuffer(unsigned int index)
> >  		planes.push_back(std::move(plane));
> >  	}
> >  
> > -	const auto &info = PixelFormatInfo::info(format_.fourcc);
> > -	if (info.isValid() && info.numPlanes() != numPlanes) {
> > +	if (formatInfo_->isValid() && formatInfo_->numPlanes() != numPlanes) {
> >  		ASSERT(numPlanes == 1u);
> 
> Not for this patch, but I guess this assert needed a
>   \todo Multiplanar support
> 
> around it?

No, when formatInfo_->numPlanes() != numPlanes, it means that we have a
multi-planar FrameBuffer with a single-planar V4L2 buffer format (e.g.
V4L2_PIX_FMT_NV12 as opposed to V4L2_PIX_FMT_NV12M). numPlanes must be 1
in that case, otherwise it's a kernel bug.

> However, this patch is just for caching the formatInfo, which seems
> reasonable so
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> > -		const size_t numColorPlanes = info.numPlanes();
> > -		planes.resize(numColorPlanes);
> > +		planes.resize(formatInfo_->numPlanes());
> >  		const FileDescriptor &fd = planes[0].fd;
> >  		size_t offset = 0;
> > -		for (size_t i = 0; i < numColorPlanes; ++i) {
> > +		for (size_t i = 0; i < planes.size(); ++i) {
> >  			planes[i].fd = fd;
> >  			planes[i].offset = offset;
> >  
> >  			/* \todo Take the V4L2 stride into account */
> > -			planes[i].length = info.planeSize(format_.size, i);
> > +			planes[i].length = formatInfo_->planeSize(format_.size, i);
> >  			offset += planes[i].length;
> >  		}
> >  	}

-- 
Regards,

Laurent Pinchart