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

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 16 Apr 2026 08:51:46 +0000
"Miclaus, Antoniu" <Antoniu.Miclaus@analog.com> wrote:

> --
> Antoniu Miclăuş
> 
> > -----Original Message-----
> > From: Jonathan Cameron <jic23@kernel.org>
> > Sent: Sunday, April 12, 2026 9:34 PM
> > To: Miclaus, Antoniu <Antoniu.Miclaus@analog.com>
> > Cc: Lars-Peter Clausen <lars@metafoo.de>; Hennerich, Michael
> > <Michael.Hennerich@analog.com>; David Lechner <dlechner@baylibre.com>;
> > Sa, Nuno <Nuno.Sa@analog.com>; Rob Herring <robh@kernel.org>; Krzysztof
> > Kozlowski <krzk+dt@kernel.org>; Conor Dooley <conor+dt@kernel.org>;
> > Olivier Moysan <olivier.moysan@foss.st.com>; linux-iio@vger.kernel.org;
> > devicetree@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH v8 0/3] iio: adc: ad4080: add support for AD4880 dual-
> > channel ADC
> > 
> > [External]
> > 
> > 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.  
> 
> The AD4880 driver has a cross-tree dependency on two SPI patches that are queued in spi/for-7.1:
> 
> - ffef4123043c ("spi: allow ancillary devices to share parent's chip selects")
> - 463279e58811 ("spi: add devm_spi_new_ancillary_device()")
> 
> The driver uses devm_spi_new_ancillary_device() with multi-CS to create an ancillary SPI device for the second channel's configuration interface, so it won't build against togreg alone.
> 
> What approach do you suggest in this situation?
Ah.  Makes sense.

Given timing, wait and if I look to have forgotten this ping me around
rc2 when I should have that 7.1 material in my base tree anyway.

thanks,

Jonathan
> 
> > 
> > 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(-)
> > >  
>