linux-kernel - Re: [PATCH v4 09/17] iio: adc: ad7768-1: Add reset gpio

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Message-ID: <20250308133045.2b3b2f49@jic23-huawei>
Date: Sat, 8 Mar 2025 13:30:45 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: Marcelo Schmitt <marcelo.schmitt1@...il.com>
Cc: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org, Sergiu Cuciurean <sergiu.cuciurean@...log.com>,
 lars@...afoo.de, Michael.Hennerich@...log.com, marcelo.schmitt@...log.com,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 linus.walleij@...aro.org, brgl@...ev.pl, lgirdwood@...il.com,
 broonie@...nel.org, dlechner@...libre.com, jonath4nns@...il.com
Subject: Re: [PATCH v4 09/17] iio: adc: ad7768-1: Add reset gpio

On Fri, 7 Mar 2025 10:42:09 -0300
Marcelo Schmitt <marcelo.schmitt1@...il.com> wrote:

> On 03/06, Jonathan Santos wrote:
> > From: Sergiu Cuciurean <sergiu.cuciurean@...log.com>
> > 
> > Depending on the controller, the default state of a gpio can vary. This
> > change excludes the probability that the dafult state of the ADC reset
> > gpio will be HIGH if it will be passed as reference in the devicetree.  
> 
> The description doesn't seem to match the changes nor the patch title. You are
> essentinally adding support for hardware reset. Change the commit description to
> reflect that.
> 
> The default state of GPIOs would not impact device reset because (in theory)
> they weren't being connected to the reset pin prevously.
Also possible some other entity was doing appropriate reset (sometimes
it's just how the system is wired - puts appropriate voltage to come out
of reset after some other action - no kernel involvement).

Agreed in general though that this is simpler described as just implementing
hardware reset and not worry about those details.

Jonathan

> 
> > 
> > Reviewed-by: David Lechner <dlechner@...libre.com>
> > Reviewed-by: Marcelo Schmitt <marcelo.schmitt@...log.com>
> > Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@...log.com>
> > Co-developed-by: Jonathan Santos <Jonathan.Santos@...log.com>
> > Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> > ---
> > v4 Changes:
> > * None.
> > 
> > v3 Changes:
> > * fixed SoB order.
> > * increased delay after finishing the reset action to 200us, as the
> >   datasheet recommends.
> > 
> > v2 Changes:
> > * Replaced usleep_range() for fsleep() and gpiod_direction_output() for 
> >   gpiod_set_value_cansleep().
> > * Reset via SPI register is performed if the Reset GPIO is not defined. 
> > ---
> >  drivers/iio/adc/ad7768-1.c | 36 ++++++++++++++++++++++++------------
> >  1 file changed, 24 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> > index 04a26e5b7d5c..86f44d28c478 100644
> > --- a/drivers/iio/adc/ad7768-1.c
> > +++ b/drivers/iio/adc/ad7768-1.c
> > @@ -166,6 +166,7 @@ struct ad7768_state {
> >  	struct completion completion;
> >  	struct iio_trigger *trig;
> >  	struct gpio_desc *gpio_sync_in;
> > +	struct gpio_desc *gpio_reset;
> >  	const char *labels[ARRAY_SIZE(ad7768_channels)];
> >  	/*
> >  	 * DMA (thus cache coherency maintenance) may require the
> > @@ -487,19 +488,30 @@ static int ad7768_setup(struct ad7768_state *st)
> >  {
> >  	int ret;
> >  
> > -	/*
> > -	 * Two writes to the SPI_RESET[1:0] bits are required to initiate
> > -	 * a software reset. The bits must first be set to 11, and then
> > -	 * to 10. When the sequence is detected, the reset occurs.
> > -	 * See the datasheet, page 70.
> > -	 */
> > -	ret = regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x3);
> > -	if (ret)
> > -		return ret;
> > +	st->gpio_reset = devm_gpiod_get_optional(&st->spi->dev, "reset",
> > +						 GPIOD_OUT_HIGH);
> > +	if (IS_ERR(st->gpio_reset))
> > +		return PTR_ERR(st->gpio_reset);
> >  
> > -	ret = regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x2);
> > -	if (ret)
> > -		return ret;
> > +	if (st->gpio_reset) {
> > +		fsleep(10);
> > +		gpiod_set_value_cansleep(st->gpio_reset, 0);
> > +		fsleep(200);
> > +	} else {
> > +		/*
> > +		 * Two writes to the SPI_RESET[1:0] bits are required to initiate
> > +		 * a software reset. The bits must first be set to 11, and then
> > +		 * to 10. When the sequence is detected, the reset occurs.
> > +		 * See the datasheet, page 70.
> > +		 */
> > +		ret = regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x3);
> > +		if (ret)
> > +			return ret;
> > +
> > +		ret = regmap_write(st->regmap, AD7768_REG_SYNC_RESET, 0x2);
> > +		if (ret)
> > +			return ret;
> > +	}
> >  
> >  	st->gpio_sync_in = devm_gpiod_get(&st->spi->dev, "adi,sync-in",
> >  					  GPIOD_OUT_LOW);
> > -- 
> > 2.34.1
> >