* For example when asking for WRITE fences then the KERNEL fences are returned
* as well. Similar when asked for READ fences then both WRITE and KERNEL
* fences are returned as well.
+ *
+ * Already used fences can be promoted in the sense that a fence with
+ * DMA_RESV_USAGE_BOOKKEEP could become DMA_RESV_USAGE_READ by adding it again
+ * with this usage. But fences can never be degraded in the sense that a fence
+ * with DMA_RESV_USAGE_WRITE could become DMA_RESV_USAGE_READ.
*/
enum dma_resv_usage {
/**
* @DMA_RESV_USAGE_BOOKKEEP: No implicit sync.
*
* This should be used by submissions which don't want to participate in
- * implicit synchronization.
+ * any implicit synchronization.
+ *
+ * The most common case are preemption fences, page table updates, TLB
+ * flushes as well as explicit synced user submissions.
*
- * The most common case are preemption fences as well as page table
- * updates and their TLB flushes.
+ * Explicit synced user user submissions can be promoted to
+ * DMA_RESV_USAGE_READ or DMA_RESV_USAGE_WRITE as needed using
+ * dma_buf_import_sync_file() when implicit synchronization should
+ * become necessary after initial adding of the fence.
*/
DMA_RESV_USAGE_BOOKKEEP
};