Hi Daniel,
Le lun., nov. 15 2021 at 15:37:16 +0100, Daniel Vetter
<daniel@xxxxxxxx> a écrit :
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.
Good question. The first reason is that a somewhat similar API was
intented before[1], but refused upstream as it was kind of re-inventing
the wheel.
The second reason, is that we want to be able to share buffers too, not
with gpu/video but with the network (zctap) and in the future with USB
(functionFS) too.
[1]:
https://lore.kernel.org/linux-iio/20210217073638.21681-1-alexandru.ardelean@xxxxxxxxxx/T/
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.
There is some dma_fence action in patch #10, which is enough for the
userspace apps to use the API.
What "horribleness" are we talking about here? It doesn't look that
scary to me, but I certainly don't have the complete picture.
Cheers,
-Paul
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
