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

[Daniel Vetter]

On Thu, Jun 25, 2020 at 3:23 PM Lionel Landwerlin
<lionel.g.landwerlin at intel.com> wrote:
>
> 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.

I asked Christian to document why timeline works like this, but I
can't find it in the kerneldoc right now. If it's missing I think we
should fix that and add the explanation, iirc it was around gpu reset
creating too much havoc otherwise.
-Daniel

>
>
> -Lionel
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch