linux-kernel - Re: [PATCH v2 06/16] iio: adc: ad7768-1: set MOSI idle state to prevent accidental reset

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Message-ID: <Z6Cp4ftJCl4F5Tce@JSANTO12-L01.ad.analog.com>
Date: Mon, 3 Feb 2025 08:34:57 -0300
From: Jonathan Santos <jonath4nns@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	lars@...afoo.de, Michael.Hennerich@...log.com,
	marcelo.schmitt@...log.com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, marcelo.schmitt1@...il.com
Subject: Re: [PATCH v2 06/16] iio: adc: ad7768-1: set MOSI idle state to
 prevent accidental reset

On 02/01, Jonathan Cameron wrote:
> On Mon, 27 Jan 2025 12:12:29 -0300
> Jonathan Santos <Jonathan.Santos@...log.com> 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@...log.com>
> 
> Ideally drag fix to start of patch set to make it obvious it can be
> picked up without the rest.  I'm not grabbing it yet as doesn't
> feel like it has enough review yet.
> 
Sure, will do.
> > ---
> > 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.
> > ---
> >  drivers/iio/adc/ad7768-1.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> > index c3cf04311c40..95ba89435652 100644
> > --- a/drivers/iio/adc/ad7768-1.c
> > +++ b/drivers/iio/adc/ad7768-1.c
> > @@ -574,6 +574,22 @@ 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
> 
> Very short line wrap.  Go up to 80 chars.  If this picks up
> some review, I can fix that whilst applying. If not do it for
> your v3.
> 
Right, i will do it in the v3.
> > +	 * 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");
>