Re: [PATCH v2 0/8] iio: add new backend framework

[Conor Dooley <conor@kernel.org>]

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On Fri, Dec 08, 2023 at 04:14:07PM +0100, Nuno Sa via B4 Relay wrote:
> This series depends on [1] and it only build on top of it. The point is
> to already speed up the reviewing of the framework. That obviously means
> that all those pacthes were dropped in v2.
> 
> v1:
>  https://lore.kernel.org/linux-iio/20231204144925.4fe9922f@jic23-huawei/T/#m222f5175273b81dbfe40b7f0daffcdc67d6cb8ff
> 
> Changes in v2:
>  - Patch 1-2 and 5
>    * new patches.
>  - Patch 6:
>    * Fixed some docs failures;
>    * Fixed a legacy 'conv' name in one of the function parameters;
>    * Added .request_buffer() and .free_buffer() ops;
>    * Refactored the helper macros;
>    * Added Olivier as Reviewer.
>  - Patch 7:
>    * Use new devm_iio_backend_request_buffer().
>  - Patch 8:
>    * Implement new .request_buffer() and .free_buffer() ops;
> 
> Also would like to mention that in v2 I'm experimenting in having the
> DMA on the backend device (as discussed with David in v1). Does not look
> to bad but as I said before, I'm not seeing a big issue if we end up
> having the buffer allocation in the frontend.
> 
> For the bindings folks:
> 
> I'm introducing a new io-backends property in the ad9467 bindings but I'm
> not sure this is the way to do it. Ideally that new property become a
> generic schema and I'm guessing I should send a PULL to?
> 
> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/iio/iio-consumer.yaml

That seems like the right thing to do to me, depending on how widespread
the use of these backends might be. What is seemingly missing though,
from this cover and from the bindings patch in the series in particular,
is an explanation of what the "iio-backends" hardware actually is.

There is some text below, but it does not seem complete to me. Is the
idea that this "backend" is shared between multiple frontend consumers?
The one example is described as being "highly focused on ADI usecases"

Thanks,
Conor.

> 
> (Jonathan, if you think that's not the right place, shout now :))
> 
> I'm also deprecating 'adi,adc-dev' as it is not relevant anymore. In the
> driver code, we are actually breaking ABI but I'm taking a more
> conservative approach in the bindings. Ideally I would also remove it in
> the bindings :).
>  
> 
> As requested here we have a small diagram that illustrated on e typical
> usage of the new framework:
> 
>                                            -------------------------------------------------------
>  ------------------                        | -----------         ------------      -------  FPGA |
>  |     ADC        |------------------------| | AXI ADC |---------| DMA CORE |------| RAM |       |
>  | (Frontend/IIO) | Serial Data (eg: LVDS) | |(backend)|---------|          |------|     |       |
>  |                |------------------------| -----------         ------------      -------       |
>  ------------------                        -------------------------------------------------------
>  
> The above is highly focused on ADI usecases. But one can see the idea...
> The frontend is the real converter and is the one registering and
> handling all the IIO interfaces. Such a device can then connect to a
> backend device for further services/configurations. In the above
> example, the backend device is an high speed core capable of handling
> the high sample rate of these ADCs so that it can push that data further
> in the pipeline (typically a DMA core) so the user can process the
> samples with minimal losses.
> 
> Jonathan, I was also tempted in including the diagram in the source
> file. Would that be a good idea?
> 
> [1]: https://lore.kernel.org/linux-iio/20231207-iio-backend-prep-v2-0-a4a33bc4d70e@analog.com
> 
> ---
> Nuno Sa (7):
>       dt-bindings: adc: ad9467: document io-backend property
>       dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'
>       driver: core: allow modifying device_links flags
>       iio: buffer-dmaengine: export buffer alloc and free functions
>       iio: add the IIO backend framework
>       iio: adc: ad9467: convert to backend framework
>       iio: adc: adi-axi-adc: move to backend framework
> 
> Olivier Moysan (1):
>       of: property: add device link support for io-backends
> 
>  .../devicetree/bindings/iio/adc/adi,ad9467.yaml    |   5 +
>  .../devicetree/bindings/iio/adc/adi,axi-adc.yaml   |   4 +-
>  MAINTAINERS                                        |   8 +
>  drivers/base/core.c                                |  14 +-
>  drivers/iio/Kconfig                                |   5 +
>  drivers/iio/Makefile                               |   1 +
>  drivers/iio/adc/Kconfig                            |   3 +-
>  drivers/iio/adc/ad9467.c                           | 242 +++++++------
>  drivers/iio/adc/adi-axi-adc.c                      | 379 +++++---------------
>  drivers/iio/buffer/industrialio-buffer-dmaengine.c |   6 +-
>  drivers/iio/industrialio-backend.c                 | 386 +++++++++++++++++++++
>  drivers/of/property.c                              |   2 +
>  include/linux/iio/adc/adi-axi-adc.h                |  68 ----
>  include/linux/iio/backend.h                        |  68 ++++
>  include/linux/iio/buffer-dmaengine.h               |   4 +-
>  15 files changed, 727 insertions(+), 468 deletions(-)
> ---
> base-commit: 330c0f834ccbdbe6a89da475cb1c56893f3a8363
> change-id: 20231120-dev-iio-backend-d14b473a1d9f
> --
> 
> Thanks!
> - Nuno Sá
> 

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