Re: [Intel-gfx] [PATCH 2/2] dma-buf: fix dma-fence-chain out of order test

[Lionel Landwerlin <lionel.g.landwerlin@intel.com>]

On 25/06/2020 16:18, Chris Wilson wrote:
> Quoting Lionel Landwerlin (2020-06-25 13:34:43)
>> There was probably a misunderstand on how the dma-fence-chain is
>> supposed to work or what dma_fence_chain_find_seqno() is supposed to
>> return.
>>
>> dma_fence_chain_find_seqno() is here to give us the fence to wait upon
>> for a particular point in the timeline. The timeline progresses only
>> when all the points prior to a given number have completed.
> Hmm, the question was what point is it supposed to wait for.
>
> For the simple chain of [1, 3], does 1 being signaled imply that all
> points up to 3 are signaled, or does 3 not being signaled imply that all
> points after 1 are not. If that's mentioned already somewhere, my bad.
> If not, could you put the answer somewhere.
> -Chris

In [1, 3], if 1 is signaled, the timeline value is 1. And find_seqno(2) 
should return NULL.


In the out_of_order selftest the chain was [1, 2, 3], 2 was signaled and 
the test was expecting no fence to be returned by find_seqno(2).

But we still have to wait on 1 to complete before find_seqno(2) can 
return NULL (as in you don't have to wait on anything).


Hope that answer the question.


-Lionel

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