For single memory plane, multiple color plane formats, e.g. V4L2_PIX_FMT_NV12, the rk3288-vpu/rockchip-vpu driver seems to return plane[0].bytesperline equal to a total of bytes per line of all color planes. This is different from what's defined in V4L2 specification:

 "When the image format is planar the bytesperline value applies to the 
  first plane and is divided by the same factor as the width field for 
  the other planes. For example the Cb and Cr planes of a YUV 4:2:0 image
  have half as many padding bytes following each line as the Y plane. To
  avoid ambiguities drivers must return a bytesperline value rounded up
  to a multiple of the scale factor."

https://www.kernel.org/doc/html/latest/media/uapi/v4l/pixfmt-v4l2.html#c.v4l2_pix_format
(Technically this is a description of the legacy structure, however the behavior of MPLANE structure for non-MPLANE formats needs to match the non-MPLANE structure.)