Re: [PATCH v2 00/12] iio: buffer-dma: write() and new DMABUF based API

[Jonathan Cameron <jic23@kernel.org>]

On Mon,  7 Feb 2022 12:59:21 +0000
Paul Cercueil <paul@crapouillou.net> wrote:

> Hi Jonathan,
> 
> This is the V2 of my patchset that introduces a new userspace interface
> based on DMABUF objects to complement the fileio API, and adds write()
> support to the existing fileio API.

Hi Paul,

It's been a little while. Perhaps you could summarize the various view
points around the appropriateness of using DMABUF for this?
I appreciate it is a tricky topic to distil into a brief summary but
I know I would find it useful even if no one else does!

Thanks,

Jonathan

> 
> Changes since v1:
> 
> - the patches that were merged in v1 have been (obviously) dropped from
>   this patchset;
> - the patch that was setting the write-combine cache setting has been
>   dropped as well, as it was simply not useful.
> - [01/12]: 
>     * Only remove the outgoing queue, and keep the incoming queue, as we
>       want the buffer to start streaming data as soon as it is enabled.
>     * Remove IIO_BLOCK_STATE_DEQUEUED, since it is now functionally the
>       same as IIO_BLOCK_STATE_DONE.
> - [02/12]:
>     * Fix block->state not being reset in
>       iio_dma_buffer_request_update() for output buffers.
>     * Only update block->bytes_used once and add a comment about why we
>       update it.
>     * Add a comment about why we're setting a different state for output
>       buffers in iio_dma_buffer_request_update()
>     * Remove useless cast to bool (!!) in iio_dma_buffer_io()
> - [05/12]:
>     Only allow the new IOCTLs on the buffer FD created with
>     IIO_BUFFER_GET_FD_IOCTL().
> - [12/12]:
>     * 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.
> 
> The patches not listed here have not been modified since v1.
> 
> Cheers,
> -Paul
> 
> Alexandru Ardelean (1):
>   iio: buffer-dma: split iio_dma_buffer_fileio_free() function
> 
> Paul Cercueil (11):
>   iio: buffer-dma: Get rid of outgoing queue
>   iio: buffer-dma: Enable buffer write support
>   iio: buffer-dmaengine: Support specifying buffer direction
>   iio: buffer-dmaengine: Enable write support
>   iio: core: Add new DMABUF interface infrastructure
>   iio: buffer-dma: Use DMABUFs instead of custom solution
>   iio: buffer-dma: Implement new DMABUF based userspace API
>   iio: buffer-dmaengine: Support new DMABUF based userspace API
>   iio: core: Add support for cyclic buffers
>   iio: buffer-dmaengine: Add support for cyclic buffers
>   Documentation: iio: Document high-speed DMABUF based API
> 
>  Documentation/driver-api/dma-buf.rst          |   2 +
>  Documentation/iio/dmabuf_api.rst              |  94 +++
>  Documentation/iio/index.rst                   |   2 +
>  drivers/iio/adc/adi-axi-adc.c                 |   3 +-
>  drivers/iio/buffer/industrialio-buffer-dma.c  | 610 ++++++++++++++----
>  .../buffer/industrialio-buffer-dmaengine.c    |  42 +-
>  drivers/iio/industrialio-buffer.c             |  60 ++
>  include/linux/iio/buffer-dma.h                |  38 +-
>  include/linux/iio/buffer-dmaengine.h          |   5 +-
>  include/linux/iio/buffer_impl.h               |   8 +
>  include/uapi/linux/iio/buffer.h               |  30 +
>  11 files changed, 749 insertions(+), 145 deletions(-)
>  create mode 100644 Documentation/iio/dmabuf_api.rst
>