To synchronize CPU access with mmap and hardware access on DMA buffers, using `DMA_BUF_IOCTL_SYNC` is required. This patch adds a function and a helper class to allow users to sync buffers more easily. Signed-off-by: Han-Lin Chen <hanlinchen@chromium.org> Co-developed-by: Harvey Yang <chenghaoyang@chromium.org> Signed-off-by: Harvey Yang <chenghaoyang@chromium.org> Reviewed-by: Milan Zamazal <mzamazal@redhat.com> Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com> Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>