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

[Laurent Pinchart]

Hi Kieran,

On Fri, Sep 03, 2021 at 09:29:40AM +0100, Kieran Bingham wrote:
> On 02/09/2021 19:26, Laurent Pinchart wrote:
> > 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.
> 
> As you're updating the conditional there anyway, could you add a short
> brief to explain that before the ASSERT please?
> 
> I don't think that extra context is clear from just the if statement.
> (Perhaps there is more context outside of the hunk maybe, but it's not
> clear from just this diff).

That's because this diff only deals with format caching :-) It's a good
point though, it's not trivial so I'll add a separate patch to document
this properly.

> >> 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