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

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Message-ID: <CAMknhBGKinZB==QHLazZ9ZkfALyj2N=rVfZfsOk22p6X9SZSrQ@mail.gmail.com>
Date:   Fri, 1 Dec 2023 11:44:45 -0600
From:   David Lechner <dlechner@...libre.com>
To:     Nuno Sá <noname.nuno@...il.com>
Cc:     nuno.sa@...log.com, 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 Fri, Dec 1, 2023 at 3:08 AM Nuno Sá <noname.nuno@...il.com> wrote:
>
> On Thu, 2023-11-30 at 17:30 -0600, David Lechner wrote:
> > On Tue, Nov 21, 2023 at 4:17 AM Nuno Sa via B4 Relay
> > <devnull+nuno.sa.analog.com@...nel.org> wrote:
> > >
> > > From: Nuno Sa <nuno.sa@...log.com>
> > >
> > > Convert the driver to use the new IIO backend framework. The device
> > > functionality is expected to be the same (meaning no added or removed
> > > features).
> >
> > Missing a devicetree bindings patch before this one?
> >
> > >
> > > Also note this patch effectively breaks ABI and that's needed so we can
> > > properly support this device and add needed features making use of the
> > > new IIO framework.
> >
> > Can you be more specific about what is actually breaking?
> >
> > >
> > > Signed-off-by: Nuno Sa <nuno.sa@...log.com>
> > > ---
> > >  drivers/iio/adc/Kconfig  |   2 +-
> > >  drivers/iio/adc/ad9467.c | 256 +++++++++++++++++++++++++++++------------------
> > >  2 files changed, 157 insertions(+), 101 deletions(-)
> > >
> > > diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
> > > index 1e2b7a2c67c6..af56df63beff 100644
> > > --- a/drivers/iio/adc/Kconfig
> > > +++ b/drivers/iio/adc/Kconfig
> > > @@ -275,7 +275,7 @@ config AD799X
> > >  config AD9467
> > >         tristate "Analog Devices AD9467 High Speed ADC driver"
> > >         depends on SPI
> > > -       depends on ADI_AXI_ADC
> > > +       select IIO_BACKEND
> > >         help
> > >           Say yes here to build support for Analog Devices:
> > >           * AD9467 16-Bit, 200 MSPS/250 MSPS Analog-to-Digital Converter
> > > diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
> > > index 5db5690ccee8..8b0402e73ace 100644
> > > --- a/drivers/iio/adc/ad9467.c
> > > +++ b/drivers/iio/adc/ad9467.c
> >
> > <snip>
> >
> > > +static int ad9467_buffer_get(struct iio_dev *indio_dev)
> >
> > perhaps a more descriptive name: ad9467_buffer_setup_optional?
> >
>
> Hmm, no strong feeling. So yeah, can do as you suggest. Even though, now that I'm
> thinking, I'm not so sure if this is just some legacy thing we had in ADI tree. I
> wonder if it actually makes sense for a device like with no buffering support?!
>
> > > +{
> > > +       struct device *dev = indio_dev->dev.parent;
> > > +       const char *dma_name;
> > > +
> > > +       if (!device_property_present(dev, "dmas"))
> > > +               return 0;
> > > +
> > > +       if (device_property_read_string(dev, "dma-names", &dma_name))
> > > +               dma_name = "rx";
> > > +
> > > +       return devm_iio_dmaengine_buffer_setup(dev, indio_dev, dma_name);
> >
> > The device tree bindings for "adi,ad9467" don't include dma properties
> > (nor should they). Perhaps the DMA lookup should be a callback to the
> > backend? Or something similar to the SPI Engine offload that we are
> > working on?
> >
>
> Oh yes, I need to update the bindings. In the link I sent you we can see my thoughts
> on this. In theory, hardwarewise, it would actually make sense for the DMA to be on
> the backend device because that's where the connection is in HW. However, since we
> want to have the IIO interface in the frontend, it would be hard to do that without
> hacking devm_iio_dmaengine_buffer_setup(). I mean, lifetime wise it would be far from
> wise to have the DMA buffer associated to a completely different device than the IIO
> parent device. I mean, one way could just be export iio_dmaengine_buffer_free() and
> iio_dmaengine_buffer_alloc() so we can actually control the lifetime of the buffer
> from the frontend device. If Jonathan is fine with this, I'm on board for it....
>
> - Nuno Sá
> >
>

I was planning on exporting iio_dmaengine_buffer_alloc() [1] for SPI
Engine offload support, so I hope that is the right way to go. ;-)

[1]: https://github.com/analogdevicesinc/linux/pull/2341/commits/71048ff83a63e9d0a5ddb9ffa331871edd6bd2a5