linux-kernel - Re: [PATCH 10/12] iio: adc: ad9467: convert to backend framework

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Message-ID: <CAMknhBEdXNkpEt-kXBez7zC0XGvo8AZ1G0Y9Y0XVr2EmpA_Qpw@mail.gmail.com>
Date:   Thu, 30 Nov 2023 18:12:12 -0600
From:   David Lechner <dlechner@...libre.com>
To:     nuno.sa@...log.com
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-iio@...r.kernel.org,
        Olivier MOYSAN <olivier.moysan@...s.st.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>
Subject: Re: [PATCH 10/12] iio: adc: ad9467: convert to backend framework

On Thu, Nov 30, 2023 at 5:30 PM David Lechner <dlechner@...libre.com> wrote:
>
> On Tue, Nov 21, 2023 at 4:17 AM Nuno Sa via B4 Relay

<snip>

> > +       st->back = devm_iio_backend_get(&spi->dev, NULL);
>
> Based on the descriptions given of IIO frontend and backend, I was
> expecting this driver to be the backend since SPI is only used to
> configure the chip while the adi-axi-adc driver is the one determining
> the scan data format, providing the DMA (INDIO_BUFFER_HARDWARE), etc.
>
> Also, from a devicetree "describe the hardware" mindset, it doesn't
> seem like this chip (AD9467) should dictate a specific backend. I know
> it doesn't make sense practlically for this chip to not use DMA given
> the high sample rate, but why should the devicetree for this chip
> require it when there is nothing intrensic about this chip itself
> related to DMA?
>

Afterthought:

Put another way, it seems like it would be much easier to say "I, the
arbitrary frontend that actually handles the data from the LVDS
outputs, need a backend that provides a SPI connection to an AD9467
chip and takes care of turning on power supplies" than it is to say
"I, the AD9467 chip frontend, need an arbitrary backend that handles
reading data from the LVDS outputs in a very specific manner that is
determined by the driver, not the hardware".