[Linaro-mm-sig] [PATCH] dma-buf/dma_resv_usage: update explicit sync documentation

[Alex Deucher]

On Tue, Jul 12, 2022 at 9:12 AM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> Make it clear that DMA_RESV_USAGE_BOOKMARK can be used for explicit synced

DMA_RESV_USAGE_BOOKKEEP?

> user space submissions as well and document the rules around adding the
> same fence with different usages.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>  include/linux/dma-resv.h | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h
> index c8ccbc94d5d2..264e27e56dff 100644
> --- a/include/linux/dma-resv.h
> +++ b/include/linux/dma-resv.h
> @@ -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_BOOKMARK could become DMA_RESV_USAGE_READ by adding it again

Same here.

With that fixed,
Acked-by: Alex Deucher <alexander.deucher at amd.com>

Alex

> + * 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
>  };
> --
> 2.25.1
>
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