linux-kernel - Re: [PATCH 7/8] iio: adc: ad7476: Support ROHM BD79105

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Message-ID: <629801b8-a647-442b-83ba-6328ecf7a977@baylibre.com>
Date: Wed, 6 Aug 2025 10:23:48 -0500
From: David Lechner <dlechner@...libre.com>
To: Matti Vaittinen <mazziesaccount@...il.com>,
 Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] iio: adc: ad7476: Support ROHM BD79105

On 8/6/25 2:04 AM, Matti Vaittinen wrote:
> The ROHM BD79105 is a simple 16-bit ADC accessible via SPI*.
> 
> The BD79105 has a CONVSTART pin, which must be set high to start the ADC
> conversion. Unlike with the ad7091 and ad7091r which also have a
> CONVSTART pin, the BD79105 requires that the pin must remain high also
> for the duration of the SPI access.
> 
> (*) Couple of words about the SPI. The BD79105 has pins named as
> CONVSTART, SCLK, DIN and DOUT. For the curious reader, DIN is not SPI
> ISO.
> 
> DIN is a signal which can be used as a chip-select. When DIN is pulled
> low, the ADC will output the completed measurement via DOUT as SCLK is
> clocked. According to the data-sheet, the DIN can also be used for
> daisy-chaining multiple ADCs. Also, DOUT can be used also for a

Leave out one of the "also"s.

> 'data-ready' -IRQ. These modes aren't supported by this driver.
> 
> Support reading ADC scale and data from the BD79105 using SPI, when DIN
> is used as a chip-select.
> 
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> ---
>  drivers/iio/adc/ad7476.c | 36 +++++++++++++++++++++++++++++++++++-
>  1 file changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/adc/ad7476.c b/drivers/iio/adc/ad7476.c
> index 1f736be09663..fc98aadc4077 100644
> --- a/drivers/iio/adc/ad7476.c
> +++ b/drivers/iio/adc/ad7476.c
> @@ -33,6 +33,7 @@ struct ad7476_chip_info {
>  	struct iio_chan_spec		convst_channel[2];
>  	void (*reset)(struct ad7476_state *);
>  	void (*conversion_pre_op)(struct ad7476_state *st);
> +	void (*conversion_post_op)(struct ad7476_state *st);
>  	bool				has_vref;
>  	bool				has_vdrive;
>  };
> @@ -64,6 +65,23 @@ static void ad7091_convst(struct ad7476_state *st)
>  	udelay(1); /* Conversion time: 650 ns max */
>  }
>  
> +static void bd79105_convst_disable(struct ad7476_state *st)
> +{
> +	if (!st->convst_gpio)
> +		return;
> +
> +	gpiod_set_value(st->convst_gpio, 0);
> +}
> +
> +static void bd79105_convst_enable(struct ad7476_state *st)
> +{
> +	if (!st->convst_gpio)
> +		return;
> +
> +	gpiod_set_value(st->convst_gpio, 1);
> +	udelay(1); /* 10ns required for conversion */

So ndelay(10)?

> +}
> +
>  static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
>  {
>  	struct iio_poll_func *pf = p;
> @@ -81,6 +99,8 @@ static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
>  	iio_push_to_buffers_with_ts(indio_dev, st->data, sizeof(st->data),
>  				    iio_get_time_ns(indio_dev));
>  done:
> +	if (st->chip_info->conversion_post_op)
> +		st->chip_info->conversion_post_op(st);
>  	iio_trigger_notify_done(indio_dev->trig);
>  
>  	return IRQ_HANDLED;
> @@ -278,6 +298,20 @@ static const struct ad7476_chip_info ltc2314_14_chip_info = {
>  	.has_vref = true,
>  };
>  
> +static const struct ad7476_chip_info bd79105_chip_info = {
> +	.convst_channel[0] = AD7091R_CONVST_CHAN(16),
> +	.convst_channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> +	/*
> +	 * The BD79105 starts ADC data conversion when thw CONVSTART is set

s/thw/the/

Also s/CONVSTART/CONVSTART line/ would be a bit more clear.

> +	 * HIGH. The CONVSTART must be kept HIGH until the data has been
> +	 * read from the ADC.
> +	 */
> +	.conversion_pre_op = bd79105_convst_enable,
> +	.conversion_post_op = bd79105_convst_disable,
> +	.has_vref = true,
> +	.has_vdrive = true,
> +};
> +
>  static const struct iio_info ad7476_info = {
>  	.read_raw = &ad7476_read_raw,
>  };
> @@ -347,7 +381,6 @@ static int ad7476_probe(struct spi_device *spi)
>  	if (st->convst_gpio)
>  		indio_dev->channels = st->chip_info->convst_channel;
>  	/* Setup default message */
> -

Random whitespace change.

>  	st->xfer.rx_buf = &st->data;
>  	st->xfer.len = indio_dev->channels[0].scan_type.storagebits / 8;
>  
> @@ -393,6 +426,7 @@ static const struct spi_device_id ad7476_id[] = {
>  	{ "ads7866", (kernel_ulong_t)&ads7866_chip_info },
>  	{ "ads7867", (kernel_ulong_t)&ads7867_chip_info },
>  	{ "ads7868", (kernel_ulong_t)&ads7868_chip_info },
> +	{ "bd79105", (kernel_ulong_t)&bd79105_chip_info },
>  	/*
>  	 * The ROHM BU79100G is identical to the TI's ADS7866 from the software
>  	 * point of view. The binding document mandates the ADS7866 to be

Unrelated to this patch, but interesting that we don't also have
an of_ lookup table.