[media] vb2: fix multiplanar read() with non-zero data_offset

If this is a multiplanar buf_type and the plane we want to read has a
non-zero data_offset, then that data_offset was not taken into account.

Note that read() or write() for formats with more than one plane is currently
not allowed, hence the use of 'planes[0]' since this is only relevant for a
single-plane format.
Signed-off-by: NHans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: NMauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/v4l2-core/videobuf2-core.c

@@ -2955,6 +2955,12 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
 		buf->queued = 0;
 		buf->size = read ? vb2_get_plane_payload(q->bufs[index], 0)
 				 : vb2_plane_size(q->bufs[index], 0);
+		/* Compensate for data_offset on read in the multiplanar case. */
+		if (is_multiplanar && read &&
+		    fileio->b.m.planes[0].data_offset < buf->size) {
+			buf->pos = fileio->b.m.planes[0].data_offset;
+			buf->size -= buf->pos;
+		}
 	} else {
 		buf = &fileio->bufs[index];
 	}