[rfc] amdgpu/sync_file shared semaphores

[Daniel Vetter]

On Tue, Mar 14, 2017 at 10:50:49AM +1000, Dave Airlie wrote:
> This contains one libdrm patch and 4 kernel patches.
> 
> The goal is to implement the Vulkan KHR_external_semaphore_fd interface
> for permanent semaphore behaviour for radv.
> 
> This code tries to enhance sync file to add the required behaviour
> (which is mostly being able to replace the fence backing the sync file),
> it also introduces new API to amdgpu to create/destroy/export/import the
> sync_files which we store in an idr there, rather than fds.
> 
> There is a possibility we should share the amdgpu_sem object tracking
> code for other drivers, maybe we should move that to sync_file as well,
> but I'm open to suggestions for whether this is a useful approach for
> other drivers.

Yeah, makes sense. I couldn't google the spec and didn't bother to figure
out where my intel khronos login went, so didn't double-check precise
semantics, just dropped a question. Few more things on the actual
sync_file stuff itself.

Really big wish here is for some igts using the debug/testing fence stuff
we have in vgem so that we can validate the corner-cases of fence
replacement and make sure nothing falls over. Especially with all the rcu
dancing sync_file/dma_fence have become non-trival, exhaustive testing is
needed here imo.

Also, NULL sync_file->fence is probably what we want for the future fences
(which android wants to keep tilers well-fed by essentially looping the
entire render pipeline on itself), so this goes into the right direction
for sure. I think, but coffee kicked in already :-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch