At some point it hopefully landed in, well, ffmpeg main repo, but for now I manually downloaded mbox and applied with git am to ffmpeg tree.
makes vaapi 4k hevc hdr decode + opencl filtering go from 6.0 fps to 6.3 fps.
./ffmpeg -hwaccel vaapi -init_hw_device opencl=ocl -filter_hw_device ocl -i ~/K38_sdcard1/Documents/iPhone11_4K-recorder_59.940HDR10.mov -vf "format=p010,hwupload,tonemap_opencl=tonemap=mobius:param=0.01:desat=0:r=tv:p=bt709:t=bt709:m=bt709:format=nv12,hwdownload,format=nv12" -c:a copy -c:s copy -c:v rawvideo -an -f nut /dev/null