Re: [PATCH v8 0/3] iio: adc: ad4080: add support for AD4880 dual-channel ADC

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 28 Mar 2026 13:40:47 +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).
> 
> 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.
I tried applying this and it's not going in cleanly (I didn't check
exactly why).  Please could you send a rebased version.  The togreg
branch should be fine I think, but maybe sanity check it against
my current testing branch as well.

Whilst this driver is making a few more assumptions about the backend
than I'd ideally like, I think it is reasonable to postpone any handling
for truely separate backends until (maybe) someone needs it.

Thanks,

Jonathan
 
> 
> Changes in v8:
>   - Drop fwnode_handle cleanup patch (now in jic23/testing)
>   - Clarify backend buffer comment to describe FPGA architecture
>     (two axi_ad408x IP instances with a packer block)
>   - Make filter_type a per-channel array instead of a single variable
>   - Restore debugfs_reg_access for AD4880 (uses channel 0 regmap),
>     based on sashiko's review
> 
> Antoniu Miclaus (3):
>   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                      | 251 ++++++++++++++----
>  drivers/iio/industrialio-backend.c            |  53 ++--
>  include/linux/iio/backend.h                   |   1 +
>  4 files changed, 282 insertions(+), 76 deletions(-)
>