lkml.org 
[lkml]   [2021]   [Nov]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 00/15] iio: buffer-dma: write() and new DMABUF based API
On Mon, Nov 15, 2021 at 02:19:10PM +0000, Paul Cercueil wrote:
> Hi Jonathan,
>
> This patchset introduces a new userspace interface based on DMABUF
> objects, to complement the existing fileio based API.
>
> The advantage of this DMABUF based interface vs. the fileio
> 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.
>
> The first few patches [01/15] to [03/15] are not really related, but
> allow to reduce the size of the patches that introduce the new API.
>
> Patch [04/15] to [06/15] enables write() support to the buffer-dma
> implementation of the buffer API, to continue the work done by
> Mihail Chindris.
>
> Patches [07/15] to [12/15] introduce the new DMABUF based API.
>
> Patches [13/15] and [14/15] add support for cyclic buffers, only through
> the new API. A cyclic buffer will be repeated on the output until the
> buffer is disabled.
>
> Patch [15/15] adds documentation about the new API.
>
> For now, the API allows you to alloc DMABUF objects and mmap() them to
> read or write the samples. It does not yet allow to import DMABUFs
> parented to other subsystems, but that should eventually be possible
> once it's wired.
>
> This patchset is inspired by the "mmap interface" that was previously
> submitted by Alexandru Ardelean and Lars-Peter Clausen, so it would be
> great if I could get a review from you guys. Alexandru's commit was
> signed with his @analog.com address but he doesn't work at ADI anymore,
> so I believe I'll need him to sign with a new email.

Why dma-buf? dma-buf looks like something super generic and useful, until
you realize that there's a metric ton of gpu/accelerator bagage piled in.
So unless buffer sharing with a gpu/video/accel/whatever device is the
goal here, and it's just for a convenient way to get at buffer handles,
this doesn't sound like a good idea.

Also if the idea is to this with gpus/accelerators then I'd really like to
see the full thing, since most likely at that point you also want
dma_fence. And once we talk dma_fence things get truly horrible from a
locking pov :-( Or well, just highly constrained and I get to review what
iio is doing with these buffers to make sure it all fits.

Cheers, Daniel

>
> Cheers,
> -Paul
>
> Alexandru Ardelean (1):
> iio: buffer-dma: split iio_dma_buffer_fileio_free() function
>
> Paul Cercueil (14):
> iio: buffer-dma: Get rid of incoming/outgoing queues
> iio: buffer-dma: Remove unused iio_buffer_block struct
> iio: buffer-dma: Use round_down() instead of rounddown()
> 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-dma: Boost performance using write-combine cache setting
> 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 | 670 ++++++++++++++----
> .../buffer/industrialio-buffer-dmaengine.c | 42 +-
> drivers/iio/industrialio-buffer.c | 49 ++
> include/linux/iio/buffer-dma.h | 43 +-
> include/linux/iio/buffer-dmaengine.h | 5 +-
> include/linux/iio/buffer_impl.h | 8 +
> include/uapi/linux/iio/buffer.h | 30 +
> 11 files changed, 783 insertions(+), 165 deletions(-)
> create mode 100644 Documentation/iio/dmabuf_api.rst
>
> --
> 2.33.0
>

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

\
 
 \ /
  Last update: 2021-11-15 15:39    [W:0.518 / U:0.260 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site