linux-kernel - Re: [PATCH v3 6/6] iio: adc: Add support for AD4000

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Message-ID: <20240609102354.02aa1128@jic23-huawei>
Date: Sun, 9 Jun 2024 10:23:54 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Nuno Sá <noname.nuno@...il.com>
Cc: Marcelo Schmitt <marcelo.schmitt@...log.com>, broonie@...nel.org,
 lars@...afoo.de, Michael.Hennerich@...log.com, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, nuno.sa@...log.com,
 dlechner@...libre.com, marcelo.schmitt1@...il.com,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org, Linus Walleij
 <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>
Subject: Re: [PATCH v3 6/6] iio: adc: Add support for AD4000

> > +
> > +static int ad4000_convert_and_acquire(struct ad4000_state *st)
> > +{
> > +	int ret;
> > +
> > +	/*
> > +	 * In 4-wire mode, the CNV line is held high for the entire
> > conversion
> > +	 * and acquisition process. In other modes st->cnv_gpio is NULL and
> > is
> > +	 * ignored (CS is wired to CNV in those cases).
> > +	 */
> > +	gpiod_set_value_cansleep(st->cnv_gpio, 1);  
> 
> Not sure it's a good practise to assume internal details as you're going for
> GPIO. I would prefer to have an explicit check for st->cnv_gpio being NULL or
> not.

Hmm. I had it in my head that this was documented behaviour, but
I can't find such in the docs, so agreed checking it makes sense.

I would be very surprised if this ever changed as it's one of the
things that makes optional gpios easy to work with but who knows!

+CC Linus and Bartosz for feedback on this one.


>   
> > +	ret = spi_sync(st->spi, &st->msg);
> > +	gpiod_set_value_cansleep(st->cnv_gpio, 0);
> > +
> > +	return ret;
> > +}
> > +

> > +static int ad4000_config(struct ad4000_state *st)
> > +{
> > +	unsigned int reg_val;
> > +
> > +	if (device_property_present(&st->spi->dev, "adi,high-z-input"))
> > +		reg_val |= FIELD_PREP(AD4000_CFG_HIGHZ, 1);
> > +
> > +	/*
> > +	 * The ADC SDI pin might be connected to controller CS line in which
> > +	 * case the write might fail. This, however, does not prevent the
> > device
> > +	 * from functioning even though in a configuration other than the
> > +	 * requested one.
> > +	 */  
> 
> This raises the question if there's any way to describe that through DT (if not
> doing it already)? So that, if SDI is connected to CS we don't even call this?
> Other question that comes to mind is that in case SDI is connected to CS, will
> all writes fail? Because if that's the case we other writes (like scale) that
> won't work and we should take care of that...

Definitely needs describing and all configuration sysfs etc needs to be read only
if we can't control it.

> 
> > +	return ad4000_write_reg(st, reg_val);
> > +}
> > +

Jonathan