linux-kernel - Re: dma-buf/sync_file: de-stage sync

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Date:	Fri, 27 May 2016 18:06:19 -0300
From:	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
To:	Dave Jones <davej@...emonkey.org.uk>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: dma-buf/sync_file: de-stage sync_file

2016-05-25 Dave Jones <davej@...emonkey.org.uk>:

> On Sat, May 21, 2016 at 05:31:53AM +0000, Linux Kernel wrote:
>  
>  >     dma-buf/sync_file: de-stage sync_file
>  >     
>  >     sync_file is useful to connect one or more fences to the file. The file is
>  >     used by userspace to track fences between drivers that share DMA bufs.
>  >     
>  >     Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
>  >     Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
>  >     Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
>  ...
>  
>  > +config SYNC_FILE
>  > +	bool "sync_file support for fences"
>  > +	default n
>  > +	select ANON_INODES
>  > +	select DMA_SHARED_BUFFER
>  > +	---help---
>  > +	  This option enables the fence framework synchronization to export
>  > +	  sync_files to userspace that can represent one or more fences.
> 
> For such a generic sounding CONFIG_ item, this is one of the more obtuse descriptions
> in a kconfig we've had in a while, and the commit message doesn't give any more
> clues as to why anyone might want to enable this.
>
> I'm guessing this is some graphics thing given that Daniel reviewed it.
> From skimming the other commits, it seems to be some Android thing ?
> Are there depends missing perhaps that might make this more obvious ?

You are right, only a few people understand this in the way I wrote. I
definitelly reword this. It is android framework to help userspace with
explict synchronization. DRM will require this, but the patches for that
did not land yet.

	Gustavo