Re: [PATCH 1/4] docs: iio: add documentation for ad3552r driver

[Marcelo Schmitt]

The doc seems to be all about the high-speed setup despite classical SPI support
being mentioned. It would be interesting to see how the regular SPI and hs
ad3552r IIO devices differ from each other (wiring connections, IIO device
interfaces (attributes, debug files, ...), any other relevant peculiarities).
Some comments about that inline.

On 03/21, Angelo Dureghello wrote:
> From: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
> 
> Add documentation for ad3552r driver, needed to describe the high-speed
> driver debugfs attributes and shows how the user may use them.
> 
> Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
> ---
...
> +==============
> +AD3552R driver
> +==============
> +
> +Device driver for Analog Devices Inc. AD35XXR series of DACs. The module name
> +is ``ad3552r``.
> +With the same module name, two different driver variants are available, the
> +``generic spi`` variant, to be used with any classic SPI controllers, and the
> +``hs`` (high speed) variant, for an ADI ``axi-dac`` (IP core) based controller
> +that allows to reach the maximum sample rate supported from the DACs, using the
> +DMA transfer and all the SPI lines available (D/QDSPI)..
Is D/QDSPI about dual and quad SPI? If so, what about saying that more clearly? 

> +The high speed driver variant is intended to be used with the ``adi-axi-dac``
> +backend support enabled, that is enabled by default when the driver is selected.
> +
> +Supported devices
> +=================
> +
> +* `AD3541R <https://www.analog.com/en/products/ad3541r.html>`_
> +* `AD3542R <https://www.analog.com/en/products/ad3542r.html>`_
> +* `AD3551R <https://www.analog.com/en/products/ad3551r.html>`_
> +* `AD3552R <https://www.analog.com/en/products/ad3552r.html>`_
> +
> +Wiring connections
> +------------------
> +
> +::
> +
> +    .-----------------.                .-------.
> +    |                 |--- D/QSPI -----|       |
> +    |   DAC IP CORE   |--- SPI S_CLK --|  DAC  |
> +    |                 |--- SPI CS -----|       |
> +    |                 |--- LDAC -------|       |
> +    |                 |--- RESET ------|       |
> +    |_________________|                |_______|

This only describes how the HDL IP connects to the DAC which is the high speed
use case. Maybe add a diagram for the regular SPI connection wiring or say that
the above is only for the hs setup?
Also, what about adding a link to the HDL documentation page?
https://analogdevicesinc.github.io/hdl/projects/ad35xxr_evb/index.html

> +
> +
> +High speed features
> +===================
> +
> +Device attributes
> +-----------------
This is only describing the debugfs file. What about also listing the usual
IIO device channels and attributes (out_voltageX_raw, out_voltageX_en, ...)?

> +
> +The following table shows the ad35xxr related device debug files, found in the
> +specific device debug folder path ``/sys/kernel/debug/iio/iio:deviceX``.
> +
> ++----------------------+-------------------------------------------------------+
> +| Debugfs device files | Description                                           |
> ++----------------------+-------------------------------------------------------+
> +| data_source          | The used data source,                                 |
> +|                      | as ``iio-buffer`` or ``backend-ramp-generator``.      |
> ++----------------------+-------------------------------------------------------+
> +