Re: [PATCH v7 0/4] iio: adc: ad4080: add support for AD4880 dual-channel ADC

[Jonathan Cameron <jonathan.cameron@huawei.com>]

On Sat, 21 Mar 2026 12:01:50 +0200
Antoniu Miclaus <antoniu.miclaus@analog.com> wrote:

> Add support for the AD4880, a dual-channel 20-bit 40MSPS SAR ADC with
> integrated fully differential amplifiers (FDA).

Given the lkml cc this got picked up by sashiko:
https://sashiko.dev/#/patchset/20260321100154.1258-1-antoniu.miclaus%40analog.com

Mixed bag on correct and (I think) incorrect stuff but take a look and fix
up anything you agree with for v8.

Thanks,

Jonathan

> 
> Architecture notes:
> 
> The AD4880 is modeled as a single IIO device rather than two independent
> devices because the channels share power supplies, a voltage reference,
> the CNV conversion clock, and a single interleaved data output stream.
> Splitting them into separate IIO devices would make synchronized
> dual-channel capture impossible from userspace.
> 
> An MFD approach does not apply here either - the channels are not
> functionally distinct sub-devices but identical ADC paths sharing a
> common data interface.
> 
> Each channel has fully independent configuration registers accessible
> through separate SPI chip selects, so per-channel regmaps are used with
> no locking between them. The data path has no software involvement at
> runtime: the CNV clock triggers simultaneous conversions and the device
> outputs an interleaved bitstream captured directly by the IIO backend
> (FPGA). spi_new_ancillary_device() handles the configuration path;
> the IIO backend handles the data path.
> 
> The debugfs_reg_access callback is not exposed for the dual-channel
> variant since the IIO framework provides a single (reg, val) interface
> with no channel parameter, and exposing only one channel would be
> misleading.
> 
> The AD4880 is a fairly unique part - having separate SPI config
> interfaces per channel with a shared interleaved data output is not
> a common pattern.
> 
> Changes in v7:
>   - Drop debugfs_reg_access for dual-channel AD4880 variant
>   - Pass struct device * to ad4080_properties_parse() instead of
>     using regmap_get_device(st->regmap[0])
>   - Use 100-column limit consistently for function signatures
>   - Add architecture summary to cover letter (per Andy's request)
> 
> Antoniu Miclaus (4):
>   iio: backend: use __free(fwnode_handle) for automatic cleanup
>   iio: backend: add devm_iio_backend_get_by_index()
>   dt-bindings: iio: adc: ad4080: add AD4880 support
>   iio: adc: ad4080: add support for AD4880 dual-channel ADC
> 
>  .../bindings/iio/adc/adi,ad4080.yaml          |  53 +++-
>  drivers/iio/adc/ad4080.c                      | 231 ++++++++++++++----
>  drivers/iio/industrialio-backend.c            |  59 +++--
>  include/linux/iio/backend.h                   |   1 +
>  4 files changed, 273 insertions(+), 71 deletions(-)
>