Re: [PATCH v3 09/10] iio: adc: ad7476: Support ROHM BD79105

[Nuno Sá]

On Fri, Aug 08, 2025 at 11:55:48AM +0300, 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
> MISO.
> 
> 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. Furthermore, DOUT can be used also for a
> '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@xxxxxxxxx>
> ---

Reviewed-by: Nuno Sá <nuno.sa@xxxxxxxxxx>

> Revision history:
>  v2 => v3:
>  - Check for missing convstart GPIO at probe.
>  - Use indirect call to convstart (via function pointer) also from the
>    ad7476_scan_direct().
> 
>  v1 => v2:
>  - Fix the conversion delay for the BD79105
>  - Drop unnecessary GPIO check from the convstart disable
>  - Drop unintended whitespace change
>  - Fix spelling
> ---
>  drivers/iio/adc/ad7476.c | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/iio/adc/ad7476.c b/drivers/iio/adc/ad7476.c
> index 6cb2cbeafbd3..1bec6657394c 100644
> --- a/drivers/iio/adc/ad7476.c
> +++ b/drivers/iio/adc/ad7476.c
> @@ -32,8 +32,10 @@ struct ad7476_chip_info {
>  	struct iio_chan_spec		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;
> +	bool				convstart_required;
>  };
>  
>  struct ad7476_state {
> @@ -64,6 +66,18 @@ static void ad7091_convst(struct ad7476_state *st)
>  	udelay(1); /* Conversion time: 650 ns max */
>  }
>  
> +static void bd79105_convst_disable(struct ad7476_state *st)
> +{
> +	gpiod_set_value_cansleep(st->convst_gpio, 0);
> +}
> +
> +static void bd79105_convst_enable(struct ad7476_state *st)
> +{
> +	gpiod_set_value_cansleep(st->convst_gpio, 1);
> +	/* Worst case, 2790 ns required for conversion */
> +	ndelay(2790);
> +}
> +
>  static irqreturn_t ad7476_trigger_handler(int irq, void  *p)
>  {
>  	struct iio_poll_func *pf = p;
> @@ -81,6 +95,8 @@ 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;
> @@ -103,6 +119,9 @@ static int ad7476_scan_direct(struct ad7476_state *st)
>  	if (ret)
>  		return ret;
>  
> +	if (st->chip_info->conversion_post_op)
> +		st->chip_info->conversion_post_op(st);
> +
>  	return be16_to_cpup((__be16 *)st->data);
>  }
>  
> @@ -273,6 +292,22 @@ static const struct ad7476_chip_info ltc2314_14_chip_info = {
>  	.has_vref = true,
>  };
>  
> +static const struct ad7476_chip_info bd79105_chip_info = {
> +	.channel[0] = AD7091R_CHAN(16),
> +	.channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> +	/*
> +	 * The BD79105 starts ADC data conversion when the CONVSTART line is
> +	 * set 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,
> +	/* BD79105 won't do conversion without convstart */
> +	.convstart_required = true,
> +	.has_vref = true,
> +	.has_vdrive = true,
> +};
> +
>  static const struct iio_info ad7476_info = {
>  	.read_raw = &ad7476_read_raw,
>  };
> @@ -332,6 +367,9 @@ static int ad7476_probe(struct spi_device *spi)
>  	if (IS_ERR(st->convst_gpio))
>  		return PTR_ERR(st->convst_gpio);
>  
> +	if (st->chip_info->convstart_required && !st->convst_gpio)
> +		return dev_err_probe(&spi->dev, -EINVAL, "No convstart GPIO\n");
> +
>  	/*
>  	 * This will never happen. Unless someone changes the channel specs
>  	 * in this driver. And if someone does, without changing the loop
> @@ -401,6 +439,7 @@ 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
> -- 
> 2.50.1
>