Hi Jonathan, Le lundi 03 avril 2023 à 10:05 -0600, Jonathan Corbet a écrit : > Paul Cercueil <paul@xxxxxxxxxxxxxxx> writes: > > One nit: > > > Document the new DMABUF based API. > > > > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx> > > Cc: Jonathan Corbet <corbet@xxxxxxx> > > Cc: linux-doc@xxxxxxxxxxxxxxx > > > > --- > > v2: - Explicitly state that the new interface is optional and is > > not implemented by all drivers. > > - The IOCTLs can now only be called on the buffer FD returned > > by > > IIO_BUFFER_GET_FD_IOCTL. > > - Move the page up a bit in the index since it is core stuff > > and not > > driver-specific. > > v3: Update the documentation to reflect the new API. > > --- > > Documentation/iio/dmabuf_api.rst | 59 > > ++++++++++++++++++++++++++++++++ > > Documentation/iio/index.rst | 2 ++ > > 2 files changed, 61 insertions(+) > > create mode 100644 Documentation/iio/dmabuf_api.rst > > > > diff --git a/Documentation/iio/dmabuf_api.rst > > b/Documentation/iio/dmabuf_api.rst > > new file mode 100644 > > index 000000000000..4d70372c7ebd > > --- /dev/null > > +++ b/Documentation/iio/dmabuf_api.rst > > @@ -0,0 +1,59 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +=================================== > > +High-speed DMABUF interface for IIO > > +=================================== > > + > > +1. Overview > > +=========== > > + > > +The Industrial I/O subsystem supports access to buffers through a > > +file-based interface, with read() and write() access calls through > > the > > +IIO device's dev node. > > + > > +It additionally supports a DMABUF based interface, where the > > userspace > > +can attach DMABUF objects (externally created) to a IIO buffer, > > and > > +subsequently use them for data transfers. > > + > > +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 useful for high-speed > > devices > > +which produce several megabytes or even gigabytes of data per > > second. > > +It does however increase the userspace-kernelspace synchronization > > +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs > > have to > > +be used for data integrity. > > + > > +2. User API > > +=========== > > + > > +As part of this interface, three new IOCTLs have been added. These > > three > > +IOCTLs have to be performed on the IIO buffer's file descriptor, > > +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl. > > + > > +``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)`` > > +---------------------------------------------------------------- > > + > > +Attach the DMABUF object, identified by its file descriptor, to > > the IIO > > +buffer. Returns zero on success, and a negative errno value on > > error. > > Rather than abusing subsections, this would be better done as a > description list: > > IIO_BUFFER_DMABUF_ATTACH_IOCTL(int) > Attach the DMABUF object, identified by its file descriptor, to > the IIO buffer. Returns zero on success, and a negative errno > value on error. Noted, thanks. Cheers, -Paul
