[rfc] drm sync objects (search for spock)

[Christian König]

Am 26.04.2017 um 05:28 schrieb Dave Airlie:
> Okay I've gone around the sun with these a few times, and
> pretty much implemented what I said last week.
>
> This is pretty much a complete revamp.
>
> 1. sync objects are self contained drm objects, they
> have a file reference so can be passed between processes.
>
> 2. Added a sync object wait interface modelled on the vulkan
> fence waiting API.
>
> 3. sync_file interaction is explicitly different than
> opaque fd passing, you import a sync file state into an
> existing syncobj, or create a new sync_file from an
> existing syncobj. This means no touching the sync file code
> at all. \o/

Doesn't that break the Vulkan requirement that if a sync_obj is exported 
to an fd and imported on the other side we get the same sync_obj again?

In other words the fd is exported and imported only once and the 
expectation is that we fence containing it will change on each signaling 
operation.

As far as I can see with the current implementation you get two 
sync_objects on in the exporting process and one in the importing one.

Regards,
Christian.

>
> I haven't used rcu anywhere here, I've used xchg to swap
> fence pointers in the hope that's safe. If this does need
> rcu'ing I suggest we do it in a follow on patch to minimise
> the review pain.
>
> Dave.
>
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