[PATCH] dma-buf: Use EXPORT_SYMBOL

[Hans Verkuil]

On Thu 11 October 2012 09:20:12 Hans Verkuil wrote:
> On Thu October 11 2012 03:11:19 Mauro Carvalho Chehab wrote:
> > Em Thu, 11 Oct 2012 09:22:34 +1000
> > Dave Airlie <airlied at gmail.com> escreveu:
> > 
> > > On Thu, Oct 11, 2012 at 4:17 AM, Alan Cox <alan at lxorguk.ukuu.org.uk> wrote:
> > > > On Wed, 10 Oct 2012 08:56:32 -0700
> > > > Robert Morell <rmorell at nvidia.com> wrote:
> > > >
> > > >> EXPORT_SYMBOL_GPL is intended to be used for "an internal implementation
> > > >> issue, and not really an interface".  The dma-buf infrastructure is
> > > >> explicitly intended as an interface between modules/drivers, so it
> > > >> should use EXPORT_SYMBOL instead.
> > > >
> > > > NAK. This needs at the very least the approval of all rights holders for
> > > > the files concerned and all code exposed by this change.
> > > 
> > > I think he has that. Maybe he just needs to list them. 
> > 
> > My understanding it that he doesn't, as the dmabuf interface exposes not only
> > the code written by this driver's author, but other parts of the Kernel.
> > 
> > Even if someone consider just the dmabuf driver, I participated and actively
> > contributed, together with other open source developers, during the 3 days 
> > discussions that happened at Linaro's forum where most of dmabuf design was
> > decided, and participated, reviewed, gave suggestions approved the code, etc
> > via email. So, even not writing the dmabuf stuff myself, I consider myself as 
> > one of the intelectual authors of the solution.
> > 
> > Also, as dmabuf will also expose media interfaces,
> 
> That's new to me. All it does is represent a buffer. It doesn't expose any
> interfaces, media or otherwise.
> 
> > my understaning is
> > that the drivers/media/ authors should also ack with this licensing
> > (possible) change. I am one of the main contributors there. Alan also has 
> > copyrights there, and at other parts of the Linux Kernel, including the driver's
> > core, from where all Linux Kernel drivers are derivative work, including this one.
> > 
> > As Alan well said, many other core Linux Kernel authors very likely share 
> > this point of view.
> > 
> > So, developers implicitly or explicitly copied in this thread that might be
> > considering the usage of dmabuf on proprietary drivers should consider
> > this email as a formal notification of my viewpoint: e. g. that I consider
> > any attempt of using DMABUF or media core/drivers together with proprietary
> > Kernelspace code as a possible GPL infringement.
> 
> As long as dmabuf uses EXPORT_SYMBOL_GPL that is definitely correct. Does your
> statement also hold if dmabuf would use EXPORT_SYMBOL? (Just asking)
> 
> BTW, we should consider changing the control framework API to EXPORT_SYMBOL_GPL.
> The number of contributors to v4l2-ctrls.c is very limited, and I have no
> problem moving that to GPL. For me dmabuf is the rare exception where I prefer
> EXPORT_SYMBOL to prevent the worse evil of forcing vendors to create incompatible
> APIs. It's a sad but true that many GPU drivers are still closed source,
> particularly in the embedded world for which dmabuf was primarily designed.

One thing I am also worried about is that if vendors can't use dmabuf for their
closed-source GPU driver, then they may not bother making GPL V4L drivers and
instead stick to a proprietary solution (e.g. OpenMAX), Which would be a shame
since we are making good progress with convincing vendors (esp. SoC vendors) to
create GPL V4L2 drivers for their hardware.

Regards,

	Hans