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

[Christian König]

Am 12.07.22 um 15:20 schrieb 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?

Crappy autocorrect and copy&paste. Thanks for pointing that out.

Christian.

>
>> 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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