[Mesa-dev] [PATCH 8/8] panfrost: Add backend targeting the DRM driver

[Eric Anholt]

Alyssa Rosenzweig <alyssa at rosenzweig.io> writes:

>> Alyssa: do you see any problem if we change to submit only one atom per
>> ioctl?
>
> I don't think so; aesthetically I don't like the extra kernel traffic,
> but that's not a real concern, and it sounds like that's the correct
> approach anyway.
>
> A big reason we submit together on non-DRM is so we can get the kernel
> to deal with dependency tracking; if we have proper syncobjs/fences,
> that doesn't matter I don't think.
>
>> Guess syncobj refs are akin to GEM handles and fences to dmabuf buffers from
>> the userspace POV?
>
> *tries to figure out what the difference between GEM handles and dmabuf
> buffers*

GEM handles: per-DRM-fd small integer references to your BOs.
Non-refcounted (GEM_CLOSE frees that number).

dmabuf: fd reference to a BO.  May be imported/exported to/from a GEM
handle using the prime interfaces.  Watch out for how it'll hand you
back the same handle for a reimport of a buffer you already have a GEM
handle to!  The fd can be passed over unix domain sockets, which is how
we move references to buffers between processes.
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