enum dma_buf_data_direction {
	DMA_BUF_BIDIRECTIONAL,
	DMA_BUF_TO_DEVICE,
	DMA_BUF_FROM_DEVICE
};

/**
 * struct dma_buf_sync_arg - Argument to 
 *
 * @start_x:   Upper left X coordinate of area to be synced.
 * Unit is format-dependent
 * @start_y:   Upper left Y coordinate of area to be synced.
 * Unit is format-dependent.
 * @width:     Width of area to be synced. Grows to the right.
 * Unit is format-dependent.
 * @height:    Height of area to be synced. Grows downwards.
 * Unit is format-dependent.
 * @direction: Intended transfer direction of data.
 * @flags:     Flags to tune the synchronizing behaviour.
 */

struct dma_buf_sync_region_arg {
	__u32 buf_identifier;
	__u32 start_x;
	__u32 start_y;
	__u32 width;
	__u32 height;
	enum dma_buf_data_direction direction;
	__u32 flags;
	__u32 pad;
};
	
/**
 * Force sync any outstanding rendering of the exporter before returning.
 * This is strictly a performance hint. The user may omit this flag to
 * speed up execution of the call, if it is known that previous rendering
 * affecting (by read or write) the synchronized area has already finished. 
 */
#define DMA_BUF_SYNC_FLAG_SYNC  (1 << 0);

/**
 * Treat @start_x as byte offset into buffer and @width as byte
 * synchronization length. The values of @start_y and @height are ignored.
 * (Separate ioctl?)
 */
#define DMA_BUF_SYNC_FLAG_LINEAR (1 << 1);

/**
 * Allow the implementation to coalesce sync_for_device calls, until either
 * a) An explicit flush
 * b) A sync for cpu call with DMA_BUF_BIDIRECTIONAL or DMA_BUF_TO_DEVICE
 *
 * Note: An implementation may choose to ignore this flag.
 */
#define DMA_BUF_SYNC_FLAG_COALESCE (1 << 2); 

/**
 * IOCTLS-
 *
 * Kernel waits should, if possible, be performed interruptible, and the
 * ioctl may sett errno to EINTR if the ioctl needs to be restarted.
 * To be discussed: Any sync operation may not affect areas outside the
 * region indicated. (Good for vmwgfx, but plays ill with cache line alignment)
 */

/**
 * Sync for CPU.
 */
#define DMA_BUF_SYNC_REGION_FOR_CPU             \ 
_IOW(DMA_BUF_BASE, 0, struct dma_buf_sync_region_arg)

/**
 * Sync for device. This is the default state of a dma-buf. 
 */
#define DMA_BUF_SYNC_REGION_FOR_DEVICE				\
_IOW(DMA_BUF_BASE, 1, struct dma_buf_sync_region_arg)

/**
 * Flush any coalesced SYNC_REGION_FOR_DEVICE
 */
#define DMA_BUF_SYNC_REGION_FLUSH		\
_IOW(DMA_BUF_BASE, 2, __u32)