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dma-buf/dma_resv_usage: update explicit sync documentation

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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: Christian König <christian.koenig@amd.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220712131201.131475-1-christian.koenig@amd.com
This commit is contained in:
Christian König 2022-07-12 14:59:36 +02:00
parent 2b066860a4
commit 0b8613a21d
1 changed files with 13 additions and 3 deletions
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16
include/linux/dma-resv.h
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@ -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 as well as page table
* updates and their TLB flushes.
* The most common case are preemption fences, page table updates, TLB
* flushes as well as explicit synced user submissions.
*
* 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
};