linux-kernel - Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

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Message-ID: <f0c709e3bf3f1ebfac29274b8f7182df9022376e.camel@gmail.com>
Date: Mon, 17 Jun 2024 08:24:19 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Paul Cercueil <paul@...pouillou.net>, Jonathan Cameron <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Vinod Koul <vkoul@...nel.org>, 
 Sumit Semwal <sumit.semwal@...aro.org>, Christian König
 <christian.koenig@....com>,  Jonathan Corbet <corbet@....net>, Nuno Sa
 <nuno.sa@...log.com>, linux-iio@...r.kernel.org, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 dmaengine@...r.kernel.org, linux-media@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface
 infrastructure

On Sat, 2024-06-15 at 13:07 +0200, Paul Cercueil wrote:
> Le dimanche 09 juin 2024 à 10:53 +0100, Jonathan Cameron a écrit :
> > On Wed,  5 Jun 2024 13:08:42 +0200
> > Paul Cercueil <paul@...pouillou.net> wrote:
> > 
> > > Add the necessary infrastructure to the IIO core to support a new
> > > optional DMABUF based interface.
> > > 
> > > With this new interface, DMABUF objects (externally created) can be
> > > attached to a IIO buffer, and subsequently used for data transfer.
> > > 
> > > A userspace application can then use this interface to share DMABUF
> > > objects between several interfaces, allowing it to transfer data in
> > > a
> > > zero-copy fashion, for instance between IIO and the USB stack.
> > > 
> > > The userspace application can also memory-map the DMABUF objects,
> > > and
> > > access the sample data directly. The advantage of doing this vs.
> > > the
> > > read() interface is that it avoids an extra copy of the data
> > > between the
> > > kernel and userspace. This is particularly userful for high-speed
> > > devices which produce several megabytes or even gigabytes of data
> > > per
> > > second.
> > > 
> > > As part of the interface, 3 new IOCTLs have been added:
> > > 
> > > IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
> > >  Attach the DMABUF object identified by the given file descriptor
> > > to the
> > >  buffer.
> > > 
> > > IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
> > >  Detach the DMABUF object identified by the given file descriptor
> > > from
> > >  the buffer. Note that closing the IIO buffer's file descriptor
> > > will
> > >  automatically detach all previously attached DMABUF objects.
> > > 
> > > IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
> > >  Request a data transfer to/from the given DMABUF object. Its file
> > >  descriptor, as well as the transfer size and flags are provided in
> > > the
> > >  "iio_dmabuf" structure.
> > > 
> > > These three IOCTLs have to be performed on the IIO buffer's file
> > > descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> > > 
> > > Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> > > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> > 
> > Need a brief note on the sign off chain.
> > What is Nuno's role in this series as he's not sending the emails and
> > not
> > marked with Co-developed-by 
> 
> That's a good question. I think he sent one revision of the patchset
> (v7 or something like that) so he added his SoB.
> 
> (Nuno: you confirm?)

exactly...

> 
> I'll add his Co-developed-by then.

Not sure if that is really deserved :)... Maybe just remove my tag.

- Nuno Sá