[PATCH libdrm] libdrm_amdgpu: add kernel semaphore support

[Christian König]

Am 11.07.2017 um 11:20 schrieb Dave Airlie:
> On 11 July 2017 at 18:36, Christian König <deathsimple at vodafone.de> wrote:
>> Am 11.07.2017 um 08:49 schrieb Dave Airlie:
>>> On 7 July 2017 at 19:07, Christian König <deathsimple at vodafone.de> wrote:
>>>> Hi Dave,
>>>>
>>>> on first glance that looks rather good to me, but there is one things I
>>>> don't really like and I strongly think Marek will absolutely agree on
>>>> that:
>>>> When we add a new CS function then let's get ride of all this
>>>> abstraction!
>>>>
>>>> The new function should get an amdgpu_device_handle and a list of chunks
>>>> to
>>>> submit, nothing else.
>>>>
>>>> When then provide helper functions to generate the chunks out of the
>>>> existing amdgpu_context_handle and amdgpu_bo_list_handle.
>>>>
>>>> That should be perfectly sufficient and extensible for future additions
>>>> as
>>>> well.
>>> Sounds tempting, but it a bit messier than it looks once I started
>>> digging into it.
>>>
>>> The main things I ran up against is the context sequence mutex protecting
>>> the
>>> kernel submissions per context which would be tricky to figure out why
>>> that is
>>> required (should we be submitting from different contexts on different
>>> threads?)
>>
>> The sequence lock is just to keep last_seq up to date and last_seq just
>> exists because of amdgpu_cs_signal_semaphore.
>>
>> We want to get ride of that, so you can drop support for this altogether in
>> the new IOCTL.
>>
>>> I'd prefer to land this then refactor a new interface, I do wonder if
>>> maybe Marek
>>> would prefer just doing this all in Mesa and avoiding these APIs a bit
>>> more :-)
>>>
>>> Once I get the syncobjs in I might look at internally refactoring the
>>> code a bit more,
>>> then a new API.
>>
>> Actually I wanted to propose just to remove the old semaphore API, it was
>> never used by Mesa or any other open source user.
> radv uses it right now until we have syncobjs.

Ah, crap. Ok in this case we can never remove it.

Anyway, the new CS IOCTL shouldn't need any support for this any more.

Just basic submission of chunks and filling in chunks from libdrm 
objects should be enough as far as I can see.

If Marek doesn't have time or doesn't want to take care of it I can send 
a patch if you want.

Christian.

>
> So it should hang around.
>
> Dave.