Re: [PATCH v4 02/17] iio: adc: ad7768-1: set MOSI idle state to prevent accidental reset

[Jonathan Cameron <jic23@kernel.org>]

On Fri, 7 Mar 2025 09:06:48 -0300
Marcelo Schmitt <marcelo.schmitt1@gmail.com> wrote:

> On 03/06, Jonathan Santos wrote:
> > Datasheet recommends Setting the MOSI idle state to high in order to
> > prevent accidental reset of the device when SCLK is free running.
> > This happens when the controller clocks out a 1 followed by 63 zeros
> > while the CS is held low.
> > 
> > Check if SPI controller supports SPI_MOSI_IDLE_HIGH flag and set it.
> > 
> > Fixes: a5f8c7da3dbe ("iio: adc: Add AD7768-1 ADC basic support")
> > Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
> > ---  
> 
> LGTM
> 
> Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Applied on assumption the answer to Marcelo's question doesn't
result in changes.

> 
> > v4 Changes:
> > * None.
> > 
> > v3 Changes:
> > * Patch moved closer to the start of the patch set.
> > 
> > v2 Changes:
> > * Only setup SPI_MOSI_IDLE_HIGH flag if the controller supports it, otherwise the driver
> >   continues the same. I realized that using bits_per_word does not avoid the problem that
> >   MOSI idle state is trying to solve. If the controller drives the MOSI low between bytes
> >   during a transfer, nothing happens.  
> 
> When you say nothing happens if the controller drives MOSI low between data
> bytes you mean the data is still good in that case? Just trying to understand
> the device behavior.
> 
> Thanks,
> Marcelo
> 
> > ---
> >  drivers/iio/adc/ad7768-1.c | 15 +++++++++++++++
> >  1 file changed, 15 insertions(+)
> > 
> > diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> > index c3cf04311c40..2e2d50ccb744 100644
> > --- a/drivers/iio/adc/ad7768-1.c
> > +++ b/drivers/iio/adc/ad7768-1.c
> > @@ -574,6 +574,21 @@ static int ad7768_probe(struct spi_device *spi)
> >  		return -ENOMEM;
> >  
> >  	st = iio_priv(indio_dev);
> > +	/*
> > +	 * Datasheet recommends SDI line to be kept high when data is not being
> > +	 * clocked out of the controller and the spi clock is free running,
> > +	 * to prevent accidental reset.
> > +	 * Since many controllers do not support the SPI_MOSI_IDLE_HIGH flag
> > +	 * yet, only request the MOSI idle state to enable if the controller
> > +	 * supports it.
> > +	 */
> > +	if (spi->controller->mode_bits & SPI_MOSI_IDLE_HIGH) {
> > +		spi->mode |= SPI_MOSI_IDLE_HIGH;
> > +		ret = spi_setup(spi);
> > +		if (ret < 0)
> > +			return ret;
> > +	}
> > +
> >  	st->spi = spi;
> >  
> >  	st->vref = devm_regulator_get(&spi->dev, "vref");
> > -- 
> > 2.34.1
> >