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

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Message-ID: <20160324143153.GA4781@joana>
Date:	Thu, 24 Mar 2016 11:31:53 -0300
From:	Gustavo Padovan <gustavo@...ovan.org>
To:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Stone <daniels@...labora.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Riley Andrews <riandrews@...roid.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
Subject: Re: [RFC 0/6] drm/fences: add in-fences to DRM

Hi Maarten,

2016-03-24 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>:

> Hey,
> 
> Op 23-03-16 om 19:47 schreef Gustavo Padovan:
> > 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
> >
> > /**
> >  * struct fence_collection - aggregate fences together
> >  * @num_fences: number of fence in the collection.
> >  * @user_data: user data.
> >  * @func: user callback to put user data.
> >  * @fences: array of @num_fences fences.
> >  */
> > struct fence_collection {
> >        int num_fences;
> >        void *user_data;
> >        collection_put_func_t func;
> >        struct fence *fences[];
> > };
> >
> >
> > The fence_collection is allocated and filled by sync_file_fences_get() and
> > atomic_commit helpers can use fence_collection_wait() to wait the fences to
> > signal.
> >
> > These patches depends on the sync ABI rework:
> >
> > https://www.spinics.net/lists/dri-devel/msg102795.html
> >
> > and the patch to de-stage the sync framework:
> >
> > https://www.spinics.net/lists/dri-devel/msg102799.html
> >
> >
> > I also hacked together some sync support into modetest for testing:
> >
> > https://git.collabora.com/cgit/user/padovan/libdrm.git/log/?h=atomic
> >
> Why did you choose to add fence_collection, rather than putting sync_file in state?
> 
> There used to be a sync_fence_wait function, which would mean you'd have everything you need.

We discussed this on #dri-devel a few days ago. The idea behind this is
to abstract sync_file from any drm driver and let only drm core deal
with sync_file. 

In the next iteration even fence_collection will be gone, so the driver
we deal only with struct fence and the fence_collection will be a
subclass of fence.

	Gustavo