Man page 9 : dma_buf_end_cpu_access

dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the cpu in the kernel context. Calls end_cpu_access to allow exporter-specific actions. Coherency is only guaranteed in the specified range for the specified access direction.

void dma_buf_end_cpu_access(struct dma_buf *  dmabuf , size_t  start , size_t  len , enum dma_data_direction  direction );

dmabuf
    [in] buffer to complete cpu access for.

start
    [in] start of range for cpu access.

len
    [in] length of range for cpu access.

direction
    [in] length of range for cpu access.

This call must always succeed.