linux-kernel - Re: [PATCH v5 7/7] docs: iio: Add documentation for AD4000

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Message-ID: <Zn7LQ8AJo0U1pzN7@debian-BULLSEYE-live-builder-AMD64>
Date: Fri, 28 Jun 2024 11:40:03 -0300
From: Marcelo Schmitt <marcelo.schmitt1@...il.com>
To: David Lechner <dlechner@...libre.com>
Cc: Marcelo Schmitt <marcelo.schmitt@...log.com>, broonie@...nel.org,
	lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org,
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, nuno.sa@...log.com, corbet@....net,
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-spi@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 7/7] docs: iio: Add documentation for AD4000

On 06/26, David Lechner wrote:
> On 6/25/24 4:55 PM, Marcelo Schmitt wrote:
> > Document wiring configurations for the AD4000 series of ADCs.
> > 
> > Signed-off-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> > ---
> >  Documentation/iio/ad4000.rst | 131 +++++++++++++++++++++++++++++++++++
> >  Documentation/iio/index.rst  |   1 +
> >  MAINTAINERS                  |   1 +
...
> > +Wiring connections
> > +------------------
> > +
> > +Devices of the AD4000 series can be connected to the SPI host controller in a
> > +few different modes.
> > +
> > +CS mode, 3-wire turbo mode
> > +^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> The datasheet also has the same diagram in _Figure 55. CS Mode, 4-Wire Turbo Mode
> Connection Diagram_. So maybe we should call this "register support mode" or
> something like that instead of mentioning 3 or 4-wire?
> 
Humm, ADAQ4003 datasheet has the same figure for CS Mode, 4-wire turbo mode
and CS mode, 4-wire with busy indicator although other datasheets have MOSI
to SDI in 4-wire turbo as you said. The register read/write functionality
sections say CNV must be brought low to access the configuration register.
I'll leave it as it is for now as I have not tested reg access with CNV high.
We can update this in the future if find out reg access to work in 4-wire mode.

> > +
> > +Datasheet "3-wire" mode is what most resembles standard SPI connection which,
> > +for these devices, comprises of connecting the controller CS line to device CNV
> > +pin and other SPI lines as usual. This configuration is (misleadingly) called
> > +"CS Mode, 3-Wire Turbo Mode" connection in datasheets.
> > +NOTE: The datasheet definition of 3-wire mode for the AD4000 series is NOT the
> > +same of standard spi-3wire mode.
> > +This is the only connection mode that allows configuration register access but
> > +it requires the SPI controller to support the ``SPI_MOSI_IDLE_HIGH`` feature.
> > +
> > +Omit the ``adi,sdi-pin`` property in device tree to select this mode.
> > +
> > +::
> > +
> > +                                         +-------------+
> > +     + ----------------------------------| SDO         |
> > +     |                                   |             |
> > +     |               +-------------------| CS          |
> > +     |               v                   |             |
> > +     |    +--------------------+         |     HOST    |
> > +     |    |        CNV         |         |             |
> > +     +--->| SDI   AD4000   SDO |-------->| SDI         |
> > +          |        SCK         |         |             |
> > +          +--------------------+         |             |
> > +                    ^                    |             |
> > +                    +--------------------| SCLK        |
> > +                                         +-------------+
> > +
> 
> I think the rest of the explanations are good.
>