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
'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@gmail.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 */
+}
+
 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
+	 * 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 */
-
 	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
-- 
2.50.1

On Wed, Aug 06, 2025 at 10:04:43AM +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
> 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
> '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.

...

> +static void bd79105_convst_disable(struct ad7476_state *st)
> +{
> +	if (!st->convst_gpio)
> +		return;

Dup code, please remove.

> +	gpiod_set_value(st->convst_gpio, 0);
> +}
> +
> +static void bd79105_convst_enable(struct ad7476_state *st)
> +{

> +	if (!st->convst_gpio)
> +		return;

With 10ns sleep in mind this is also unneeded check.

> +	gpiod_set_value(st->convst_gpio, 1);

> +	udelay(1); /* 10ns required for conversion */

We have ndelay(). But I believe toggling GPIO is much longer operation.

> +}

...

> @@ -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 */
> -
>  	st->xfer.rx_buf = &st->data;
>  	st->xfer.len = indio_dev->channels[0].scan_type.storagebits / 8;

Stray change.


-- 
With Best Regards,
Andy Shevchenko

On 06/08/2025 23:26, Andy Shevchenko wrote:
> On Wed, Aug 06, 2025 at 10:04:43AM +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
>> 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
>> '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.
> 
> ...
> 
>> +
>> +static void bd79105_convst_enable(struct ad7476_state *st)
>> +{
> 
>> +	if (!st->convst_gpio)
>> +		return;
> 
> With 10ns sleep in mind this is also unneeded check.
> 
>> +	gpiod_set_value(st->convst_gpio, 1);
> 
>> +	udelay(1); /* 10ns required for conversion */
> 
> We have ndelay(). But I believe toggling GPIO is much longer operation.

Thanks for the review Andy.

As I replied to David, this 10nS is rubbish. I need to clarify the right 
value.


Yours,
	-- Matti

On Thu, Aug 7, 2025 at 9:31 AM Matti Vaittinen <mazziesaccount@gmail.com> wrote:
> On 06/08/2025 23:26, Andy Shevchenko wrote:
> > On Wed, Aug 06, 2025 at 10:04:43AM +0300, Matti Vaittinen wrote:

...

> >> +static void bd79105_convst_enable(struct ad7476_state *st)
> >> +{
> >
> >> +    if (!st->convst_gpio)
> >> +            return;
> >
> > With 10ns sleep in mind this is also unneeded check.
> >
> >> +    gpiod_set_value(st->convst_gpio, 1);
> >
> >> +    udelay(1); /* 10ns required for conversion */
> >
> > We have ndelay(). But I believe toggling GPIO is much longer operation.
>
> Thanks for the review Andy.
>
> As I replied to David, this 10nS is rubbish. I need to clarify the right
> value.

Then probably you want to call fsleep(), and if the value is few /
dozens of useconds, I would drop the check for GPIO and leave with a
small delay.

-- 
With Best Regards,
Andy Shevchenko

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@gmail.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.

Thanks again David.

On 06/08/2025 18:23, David Lechner wrote:
> 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@gmail.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

...

>> +
>> +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)?

Thanks for pointing this out. This delay was something I thought I must 
clarify! This 10nS comment got just copied from the existing convstart, 
it probably is wrong for the bd79105.

...
  >>   	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.

I am not sure what is the value of having the of_match table with the 
SPI devices. The SPI-ID will in any case be required for the module 
loading, and it can be built based on the DT compatible.

I admit I don't really know all the dirty details but, from what I can 
say, the only potential use would be if this driver supported two 
variants (which needed to be distinguished) with identical 
chip-compatible but different vendor part. I accept all education (also) 
on this matter though :)

Yours,
	-- Matti