linux-kernel - Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer sharing mechanism

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Message-ID: <20111209225056.GL7969@morell.nvidia.com>
Date:	Fri, 9 Dec 2011 14:50:56 -0800
From:	Robert Morell <rmorell@...dia.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Sumit Semwal <sumit.semwal@...com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"jesse.barker@...aro.org" <jesse.barker@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"daniel@...ll.ch" <daniel@...ll.ch>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [Linaro-mm-sig] [RFC v2 1/2] dma-buf: Introduce dma buffer
 sharing mechanism

On Mon, Dec 05, 2011 at 09:18:48AM -0800, Arnd Bergmann wrote:
> On Friday 02 December 2011, Sumit Semwal wrote:
> > This is the first step in defining a dma buffer sharing mechanism.
> 
[...]
> 
> > +	return dmabuf;
> > +}
> > +EXPORT_SYMBOL(dma_buf_export);
> 
> I agree with Konrad, this should definitely be EXPORT_SYMBOL_GPL,
> because it's really a low-level function that I would expect
> to get used by in-kernel subsystems providing the feature to
> users and having back-end drivers, but it's not the kind of thing
> we want out-of-tree drivers to mess with.

Is this really necessary?  If this is intended to be a
lowest-common-denominator between many drivers to allow buffer sharing,
it seems like it needs to be able to be usable by all drivers.

If the interface is not accessible then I fear many drivers will be
forced to continue to roll their own buffer sharing mechanisms (which is
exactly what we're trying to avoid here, needless to say).

- Robert
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