linux-kernel - Re: [RFC 0/6] drm/fences: add in-fences to DRM

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Date:	Thu, 24 Mar 2016 11:39:13 -0300
From:	Gustavo Padovan <gustavo@...ovan.org>
To:	Inki Dae <inki.dae@...sung.com>
Cc:	dri-devel@...ts.freedesktop.org,
	Daniel Stone <daniels@...labora.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Arve Hjønnevåg <arve@...roid.com>,
	linux-kernel@...r.kernel.org,
	Riley Andrews <riandrews@...roid.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>
Subject: Re: [RFC 0/6] drm/fences: add in-fences to DRM

Hi Inki,

2016-03-24 Inki Dae <inki.dae@...sung.com>:

> Hi,
> 
> 2016년 03월 24일 03:47에 Gustavo Padovan 이(가) 쓴 글:
> > From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> >
> > Hi,
> >
> > This is a first proposal to discuss the addition of in-fences support
> > to DRM. It adds a new struct to fence.c to abstract the use of sync_file
> > in DRM drivers. The new struct fence_collection contains a array with all
> > fences that a atomic commit needs to wait on
> 
> As I mentioned already like below,
> http://www.spinics.net/lists/dri-devel/msg103225.html
> 
> I don't see why Android specific thing is tried to propagate to Linux DRM. In Linux mainline, it has already implicit sync interfaces for DMA devices called dma fence which forces registering a fence obejct to DMABUF through a reservation obejct when a dmabuf object is created. However, Android sync driver creates a new file for a sync object and this would have different point of view.
> 
> Is there anyone who can explan why Android specific thing is tried to spread into Linux DRM? Was there any consensus to use Android sync driver - which uses explicit sync interfaces - as Linux standard?

Because we want explicit fencing as the Linux standard in the future to
be able to do smart scheduling, e.g., send async jobs to the gpu and at
the same time send async atomic commits with sync_file fd attached so
they can wait the GPU to finish and we don't block in userspace anymore,
quite similar to what Android does.

This would still use dma-buf fences in the driver level, but it has a
lot more advantages than implicit fencing.

	Gustavo