Commit 0b8613a2 authored by Christian König's avatar Christian König
Browse files

dma-buf/dma_resv_usage: update explicit sync documentation 



Make it clear that DMA_RESV_USAGE_BOOKKEEP can be used for explicit synced
user space submissions as well and document the rules around adding the
same fence with different usages.

Signed-off-by: default avatarChristian König <christian.koenig@amd.com>
Reviewed-by: default avatarBas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220712131201.131475-1-christian.koenig@amd.com
parent 2b066860

include/linux/dma-resv.h

+13 −3
Original line number Diff line number Diff line
@@ -62,6 +62,11 @@ struct dma_resv_list; 
 * 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 {

	/**
@@ -98,10 +103,15 @@ 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

};