[PATCH v2 0/8] iio: adc: dfsdm: add scaling support

[Olivier Moysan <olivier.moysan@foss.st.com>]

The aim of this serie is to add scaling support to STM32 DFSDM
peripheral in the analog context.

The DFSDM currently operates as a consumer of IIO channels
provided by a generic SD modulator. As previously discussed in RFC [1],
this topology is not suitable for implementing scaling.

This series brings the integration of the DFSDM driver with the new 
IIO backend framework [2], enabling the DFSDM IIO device to offer 
scaling feature based on reference voltage data obtained from the
IIO SD modulator backend. This generic SD modulator backend takes the
place of the former SD modulator, used with legacy implementation.

The DFSDM driver has been updated to adopt the generic ADC channel
binding [3]. The reasons for this include:
- Reducing the use of proprietary properties
- Simplifying the coexistence of legacy and new backend bindings
- Prepare the support of the MDF peripheral on STM32MP25 SoC

Backward compatibility is maintained through legacy support.

This series extends the backend framework with the following APIs:
- iio_backend_read_raw:
	This API is intented to retrieve the voltage information from the
	backend. It is based on IIO framework read_raw API.
- iio_backend_disable / iio_backend_enable:
	backend enable/disable to be used for PM management
- devm_iio_backend_fwnode_get
	Intended for parsing DT subnodes to allow generic channel binding
	support, as generic channel DT nodes are not populated as devices.

[1]: https://lore.kernel.org/lkml/20200204101008.11411-1-olivier.moysan@st.com/
[2]: https://lore.kernel.org/all/20240206-iio-backend-v9-0-df66d159c000@analog.com/
[3]: devicetree/bindings/iio/adc/adc.yaml

Changes in v2:
- Update enable/disable backend API
- Rename devm_iio_backend_subnode_get(), as devm_iio_backend_fwnode_get()
- Update iio_backend_read_raw() prototype to fully match IIO framework
  read_raw callback prototype.
- Change st,adc-channel-type property name and type in DFSDM binding
- Remove sd-backend and rename ads1201 compatibles in SD binding

Conor, in this v2, I left the SD modulator driver & binding unchanged,
regarding the naming issue you raised previously.

The problem here is that we have two versions of the generic sigma delta
modulator driver: one for legacy support and a new one to support new
binding. Maybe an alternate, is to rename former sd modulator as
"legacy" or something similar.
I will address this point in a v3 if necessary.

Olivier Moysan (8):
  iio: add read raw service to iio backend framework
  iio: add enable and disable services to iio backend framework
  iio: add child nodes support in iio backend framework
  dt-bindings: iio: dfsdm: move to backend framework
  dt-bindings: iio: add sigma delta modulator backend
  iio: adc: stm32-dfsdm: adopt generic channels bindings
  iio: add sd modulator generic iio backend
  iio: adc: stm32-dfsdm: add scaling support to dfsdm

 .../iio/adc/sd-modulator-backend.yaml         |  39 +++
 .../bindings/iio/adc/st,stm32-dfsdm-adc.yaml  | 157 ++++++++-
 drivers/iio/adc/Kconfig                       |  11 +
 drivers/iio/adc/Makefile                      |   1 +
 drivers/iio/adc/sd_adc_backend.c              | 117 +++++++
 drivers/iio/adc/stm32-dfsdm-adc.c             | 302 +++++++++++++++---
 drivers/iio/industrialio-backend.c            | 108 +++++--
 include/linux/iio/backend.h                   |  10 +-
 8 files changed, 679 insertions(+), 66 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/sd-modulator-backend.yaml
 create mode 100644 drivers/iio/adc/sd_adc_backend.c


base-commit: 2dfa1b7bfc07e58acb9f9eaa8c871f37189dbfee
-- 
2.25.1