Re: [PATCH v2 3/6] iio: ad7949: Support configuration read-back

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 7 May 2019 14:53:32 -0500
Adam Michaelis <adam.michaelis@collins.com> wrote:

> On Sun, May 5, 2019 at 9:42 AM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Thu,  2 May 2019 11:14:29 -0500
> > Adam Michaelis <adam.michaelis@rockwellcollins.com> wrote:
> >  
> > > Adds device tree parameter to set the configuration read-back bit
> > > in the configuration register to tell the AD7949 to include the value of
> > > the configuration register at the time the current sample was acquired
> > > when reading from the part.
> > >
> > > Further work must be done to make read-back information available to
> > > consumer.  
> >
> > This needs some explanation of why it is useful at all. I'm certainly unclear
> > on why it would be useful to configure this at boot time.
> >
> > Code looks fine.
> >
> > Jonathan
> >  
> The configuration read-back feature is being maintained from the
> original version of this driver. Before adding the device tree entry,
> there was no way to change this setting other than debugfs raw access
> to the SPI interface, and there is still no access to the returned
> configuration data should the feature be enabled. I would be willing
> to remove the feature altogether, but wanted to tread softly on
> existing features.
Ah. Makes sense.  My gut feeling is to drop it.

Anyone at Analog have a view on this?

Thanks,

Jonathan

> 
> Adam
> > >
> > > Signed-off-by: Adam Michaelis <adam.michaelis@rockwellcollins.com>
> > > ---
> > >       V2: Add some defines to reduce use of magic numbers.
> > > ---
> > >  drivers/iio/adc/ad7949.c | 12 +++++++++++-
> > >  1 file changed, 11 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > > index afc1361af5fb..7820e1097787 100644
> > > --- a/drivers/iio/adc/ad7949.c
> > > +++ b/drivers/iio/adc/ad7949.c
> > > @@ -69,6 +69,7 @@ struct ad7949_adc_spec {
> > >   * @iio_dev: reference to iio structure
> > >   * @spi: reference to spi structure
> > >   * @ref_sel: selected reference voltage source
> > > + * @cfg_readback: whether reads will include configuration data
> > >   * @resolution: resolution of the chip
> > >   * @cfg: copy of the configuration register
> > >   * @current_channel: current channel in use
> > > @@ -80,6 +81,7 @@ struct ad7949_adc_chip {
> > >       struct iio_dev *indio_dev;
> > >       struct spi_device *spi;
> > >       enum ad7949_ref_sel ref_sel;
> > > +     bool cfg_readback;
> > >       u8 resolution;
> > >       u16 cfg;
> > >       unsigned int current_channel;
> > > @@ -283,7 +285,11 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
> > >                       AD7949_CFG_REF_SEL_MASK;
> > >       adc_config |= (AD7949_CFG_SEQ_DISABLED << AD7949_CFG_SEQ_SHIFT) &
> > >                       AD7949_CFG_SEQ_MASK;
> > > -     adc_config |= AD7949_CFG_READBACK_DIS;
> > > +
> > > +     if (ad7949_adc->cfg_readback)
> > > +             adc_config |= AD7949_CFG_READBACK_EN;
> > > +     else
> > > +             adc_config |= AD7949_CFG_READBACK_DIS;
> > >
> > >       ret = ad7949_spi_write_cfg(ad7949_adc,
> > >                       adc_config,
> > > @@ -331,6 +337,10 @@ static int ad7949_spi_probe(struct spi_device *spi)
> > >       indio_dev->num_channels = spec->num_channels;
> > >       ad7949_adc->resolution = spec->resolution;
> > >
> > > +     ad7949_adc->cfg_readback = of_property_read_bool(
> > > +                     ad7949_adc->indio_dev->dev.of_node,
> > > +                     "adi,cfg-readback");
> > > +
> > >       ret = of_property_read_u32(ad7949_adc->indio_dev->dev.of_node,
> > >                       "adi,reference-select",
> > >                       &temp);  
> >  
> 
> --