linux-kernel - Re: [RFC 0/5] rework fences on struct sync

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Message-ID: <576CFD0B.6000501@amd.com>
Date:	Fri, 24 Jun 2016 11:27:39 +0200
From:	Christian König <christian.koenig@....com>
To:	Gustavo Padovan <gustavo@...ovan.org>,
	<dri-devel@...ts.freedesktop.org>
CC:	<marcheu@...gle.com>, Daniel Stone <daniels@...labora.com>,
	<seanpaul@...gle.com>, Daniel Vetter <daniel.vetter@...ll.ch>,
	<linux-kernel@...r.kernel.org>,
	<laurent.pinchart@...asonboard.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>,
	<m.chehab@...sung.com>
Subject: Re: [RFC 0/5] rework fences on struct sync_file

Am 23.06.2016 um 17:29 schrieb Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
>
> Hi all,
>
> This is an attempt to improve fence support on Sync File. The basic idea
> is to have only sync_file->fence and store all fences there, either as
> normal fences or fence_arrays. That way we can remove some potential
> duplication when using fence_array with sync_file: the duplication of the array
> of fences and the duplication of fence_add_callback() for all fences.
>
> Now when creating a new sync_file during the merge process sync_file_set_fence()
> will set sync_file->fence based on the number of fences for that sync_file. If
> there is more than one fence a fence_array is created. One important advantage
> approach is that we only add one fence callback now, no matter how many fences
> there are in a sync_file - the individual callbacks are added by fence_array.
>
> Two fence ops had to be created to help abstract the difference between handling
> fences and fences_arrays: .teardown() and .get_fences(). The former run needed
> on fence_array, and the latter just return a copy of all fences in the fence.
> I'm not so sure about adding those two, speacially .get_fences(). What do you
> think?

Clearly not a good idea to add this a fence ops, cause those are 
specialized functions for only a certain fence implementation (the 
fence_array).

What you should do is try to cast the fence in your sync file using 
to_fence_array() and then you can access the fences in the array.

Regards,
Christian.

>
> Please comment! Thanks.
>
> 	Gustavo
> ---
>
> Gustavo Padovan (5):
>    dma-buf/fence: add .teardown() ops
>    dma-buf/fence-array: add fence_array_teardown()
>    dma-buf/fence: add .get_fences() ops
>    dma-buf/fence-array: add fence_array_get_fences()
>    dma-buf/sync_file: rework fence storage in struct file
>
>   drivers/dma-buf/fence-array.c        |  30 ++++++++
>   drivers/dma-buf/fence.c              |  21 ++++++
>   drivers/dma-buf/sync_file.c          | 129 +++++++++++++++++++++++++----------
>   drivers/staging/android/sync_debug.c |   5 +-
>   include/linux/fence.h                |  10 +++
>   include/linux/sync_file.h            |  12 ++--
>   6 files changed, 161 insertions(+), 46 deletions(-)
>