[PATCH] staging: iio: ad7780: Add gain & filter gpio support

[PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Giuliano Belinassi]

Previously, the AD7780 driver only supported gpio for the 'powerdown'
pin. This commit adds suppport for the 'gain' and 'filter' pin.

Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
---
 drivers/staging/iio/adc/ad7780.c       | 61 ++++++++++++++++++++++++--
 include/linux/iio/adc/ad_sigma_delta.h |  5 +++
 2 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/iio/adc/ad7780.c b/drivers/staging/iio/adc/ad7780.c
index c4a85789c2db..69794f06dbcd 100644
--- a/drivers/staging/iio/adc/ad7780.c
+++ b/drivers/staging/iio/adc/ad7780.c
@@ -39,6 +39,9 @@
 #define AD7170_PATTERN		(AD7780_PAT0 | AD7170_PAT2)
 #define AD7170_PATTERN_MASK	(AD7780_PAT0 | AD7780_PAT1 | AD7170_PAT2)
 
+#define AD7780_GAIN_GPIO	0
+#define AD7780_FILTER_GPIO	1
+
 struct ad7780_chip_info {
 	struct iio_chan_spec	channel;
 	unsigned int		pattern_mask;
@@ -50,6 +53,8 @@ struct ad7780_state {
 	const struct ad7780_chip_info	*chip_info;
 	struct regulator		*reg;
 	struct gpio_desc		*powerdown_gpio;
+	struct gpio_desc		*gain_gpio;
+	struct gpio_desc		*filter_gpio;
 	unsigned int	gain;
 
 	struct ad_sigma_delta sd;
@@ -115,18 +120,51 @@ static int ad7780_read_raw(struct iio_dev *indio_dev,
 	return -EINVAL;
 }
 
+static int ad7780_write_raw(struct iio_dev *indio_dev,
+			    struct iio_chan_spec const *chan,
+			    int val,
+			    int val2,
+			    long m)
+{
+	struct ad7780_state *st = iio_priv(indio_dev);
+
+	if (m != IIO_CHAN_INFO_RAW)
+		return -EINVAL;
+
+	if (st->chip_info->is_ad778x) {
+		switch(val) {
+		case AD7780_GAIN_GPIO:
+			gpiod_set_value(st->gain_gpio, val2);
+		break;
+		case AD7780_FILTER_GPIO:
+			gpiod_set_value(st->filter_gpio, val2);
+		break;
+		default:
+			return -EINVAL;
+		}
+	}
+
+	return 0;
+}
+
 static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
 				     unsigned int raw_sample)
 {
 	struct ad7780_state *st = ad_sigma_delta_to_ad7780(sigma_delta);
 	const struct ad7780_chip_info *chip_info = st->chip_info;
+	int val;
 
 	if ((raw_sample & AD7780_ERR) ||
 	    ((raw_sample & chip_info->pattern_mask) != chip_info->pattern))
 		return -EIO;
 
 	if (chip_info->is_ad778x) {
-		if (raw_sample & AD7780_GAIN)
+		val = raw_sample & AD7780_GAIN;
+
+		if (val != gpiod_get_value(st->gain_gpio))
+			return -EIO;
+
+		if (val)
 			st->gain = 1;
 		else
 			st->gain = 128;
@@ -141,18 +179,20 @@ static const struct ad_sigma_delta_info ad7780_sigma_delta_info = {
 	.has_registers = false,
 };
 
-#define AD7780_CHANNEL(bits, wordsize) \
+#define AD7170_CHANNEL(bits, wordsize) \
 	AD_SD_CHANNEL_NO_SAMP_FREQ(1, 0, 0, bits, 32, wordsize - bits)
+#define AD7780_CHANNEL(bits, wordsize) \
+	AD_SD_CHANNEL_GAIN_FILTER(1, 0, 0, bits, 32, wordsize - bits)
 
 static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
 	[ID_AD7170] = {
-		.channel = AD7780_CHANNEL(12, 24),
+		.channel = AD7170_CHANNEL(12, 24),
 		.pattern = AD7170_PATTERN,
 		.pattern_mask = AD7170_PATTERN_MASK,
 		.is_ad778x = false,
 	},
 	[ID_AD7171] = {
-		.channel = AD7780_CHANNEL(16, 24),
+		.channel = AD7170_CHANNEL(16, 24),
 		.pattern = AD7170_PATTERN,
 		.pattern_mask = AD7170_PATTERN_MASK,
 		.is_ad778x = false,
@@ -173,6 +213,7 @@ static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
 
 static const struct iio_info ad7780_info = {
 	.read_raw = ad7780_read_raw,
+	.write_raw = ad7780_write_raw,
 };
 
 static int ad7780_probe(struct spi_device *spi)
@@ -222,6 +263,18 @@ static int ad7780_probe(struct spi_device *spi)
 		goto error_disable_reg;
 	}
 
+	if (st->chip_info->is_ad778x) {
+		st->gain_gpio = devm_gpiod_get_optional(&spi->dev,
+							"gain",
+							GPIOD_OUT_HIGH);
+		if (IS_ERR(st->gain_gpio)) {
+			ret = PTR_ERR(st->gain_gpio);
+			dev_err(&spi->dev, "Failed to request gain GPIO: %d\n",
+				ret);
+			goto error_disable_reg;
+		}
+	}
+
 	ret = ad_sd_setup_buffer_and_trigger(indio_dev);
 	if (ret)
 		goto error_disable_reg;
diff --git a/include/linux/iio/adc/ad_sigma_delta.h b/include/linux/iio/adc/ad_sigma_delta.h
index 730ead1a46df..6cadab6fd5fd 100644
--- a/include/linux/iio/adc/ad_sigma_delta.h
+++ b/include/linux/iio/adc/ad_sigma_delta.h
@@ -173,6 +173,11 @@ int ad_sd_validate_trigger(struct iio_dev *indio_dev, struct iio_trigger *trig);
 	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
 		_storagebits, _shift, NULL, IIO_VOLTAGE, 0)
 
+#define AD_SD_CHANNEL_GAIN_FILTER(_si, _channel, _address, _bits, \
+	_storagebits, _shift) \
+	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
+		_storagebits, _shift, NULL, IIO_VOLTAGE, BIT(IIO_CHAN_INFO_RAW))
+
 #define AD_SD_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
 	__AD_SD_CHANNEL(_si, 0, -1, _address, _bits, \
 		_storagebits, _shift, NULL, IIO_TEMP, \
-- 
2.19.1

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Popa, Stefan Serban]

On Mi, 2018-11-21 at 16:04 -0200, Giuliano Belinassi wrote:
> Previously, the AD7780 driver only supported gpio for the 'powerdown'
> pin. This commit adds suppport for the 'gain' and 'filter' pin.
Hey,

Comments inline.
> 
> Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
> ---
>  drivers/staging/iio/adc/ad7780.c       | 61 ++++++++++++++++++++++++--
>  include/linux/iio/adc/ad_sigma_delta.h |  5 +++
>  2 files changed, 62 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7780.c
> b/drivers/staging/iio/adc/ad7780.c
> index c4a85789c2db..69794f06dbcd 100644
> --- a/drivers/staging/iio/adc/ad7780.c
> +++ b/drivers/staging/iio/adc/ad7780.c
> @@ -39,6 +39,9 @@
>  #define AD7170_PATTERN		(AD7780_PAT0 | AD7170_PAT2)
>  #define AD7170_PATTERN_MASK	(AD7780_PAT0 | AD7780_PAT1 |
> AD7170_PAT2)
>  
> +#define AD7780_GAIN_GPIO	0
> +#define AD7780_FILTER_GPIO	1
> +
>  struct ad7780_chip_info {
>  	struct iio_chan_spec	channel;
>  	unsigned int		pattern_mask;
> @@ -50,6 +53,8 @@ struct ad7780_state {
>  	const struct ad7780_chip_info	*chip_info;
>  	struct regulator		*reg;
>  	struct gpio_desc		*powerdown_gpio;
> +	struct gpio_desc		*gain_gpio;
> +	struct gpio_desc		*filter_gpio;
>  	unsigned int	gain;
>  
>  	struct ad_sigma_delta sd;
> @@ -115,18 +120,51 @@ static int ad7780_read_raw(struct iio_dev
> *indio_dev,
>  	return -EINVAL;
>  }
>  
> +static int ad7780_write_raw(struct iio_dev *indio_dev,
> +			    struct iio_chan_spec const *chan,
> +			    int val,
> +			    int val2,
> +			    long m)
> +{
> +	struct ad7780_state *st = iio_priv(indio_dev);
> +
> +	if (m != IIO_CHAN_INFO_RAW)
> +		return -EINVAL;
> +
> +	if (st->chip_info->is_ad778x) {
> +		switch(val) {
> +		case AD7780_GAIN_GPIO:

I think that instead of setting the gain directly, we should use
the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780 datasheet there
is a formula from which the output code can be calculated:
Code = 2^(N − 1)
× [(AIN × Gain /VREF) + 1]. So, by setting the scale from user space, the
driver can calculate the correct gain by using the formula above. Also, it
would be useful to introduce scale available.
Furthermore, there is a new
ad7124 adc driver which does this exact thing. Take a look here: https://gi
thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.c#L337.

> +			gpiod_set_value(st->gain_gpio, val2);
> +		break;
> +		case AD7780_FILTER_GPIO:

The attribute that should be used to configure the filter gpio is
IIO_CHAN_INFO_SAMP_FREQ. So, we should have 10 Hz and 16.7 Hz available
sampling frequencies. If from user space the 10 Hz sampling freq is
requested, then we set the FILTER pin high, while for 16.7 Hz the FILTER
pin will be low.

> +			gpiod_set_value(st->filter_gpio, val2);
> +		break;
> +		default:
> +			return -EINVAL;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
>  				     unsigned int raw_sample)
>  {
>  	struct ad7780_state *st = ad_sigma_delta_to_ad7780(sigma_delta);
>  	const struct ad7780_chip_info *chip_info = st->chip_info;
> +	int val;
>  
>  	if ((raw_sample & AD7780_ERR) ||
>  	    ((raw_sample & chip_info->pattern_mask) != chip_info-
> >pattern))
>  		return -EIO;
>  
>  	if (chip_info->is_ad778x) {
> -		if (raw_sample & AD7780_GAIN)
> +		val = raw_sample & AD7780_GAIN;
> +
> +		if (val != gpiod_get_value(st->gain_gpio))
> +			return -EIO;
> +
> +		if (val)
>  			st->gain = 1;
>  		else
>  			st->gain = 128;
> @@ -141,18 +179,20 @@ static const struct ad_sigma_delta_info
> ad7780_sigma_delta_info = {
>  	.has_registers = false,
>  };
>  
> -#define AD7780_CHANNEL(bits, wordsize) \
> +#define AD7170_CHANNEL(bits, wordsize) \
>  	AD_SD_CHANNEL_NO_SAMP_FREQ(1, 0, 0, bits, 32, wordsize - bits)
> +#define AD7780_CHANNEL(bits, wordsize) \
> +	AD_SD_CHANNEL_GAIN_FILTER(1, 0, 0, bits, 32, wordsize - bits)
>  
>  static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
>  	[ID_AD7170] = {
> -		.channel = AD7780_CHANNEL(12, 24),
> +		.channel = AD7170_CHANNEL(12, 24),
>  		.pattern = AD7170_PATTERN,
>  		.pattern_mask = AD7170_PATTERN_MASK,
>  		.is_ad778x = false,
>  	},
>  	[ID_AD7171] = {
> -		.channel = AD7780_CHANNEL(16, 24),
> +		.channel = AD7170_CHANNEL(16, 24),
>  		.pattern = AD7170_PATTERN,
>  		.pattern_mask = AD7170_PATTERN_MASK,
>  		.is_ad778x = false,
> @@ -173,6 +213,7 @@ static const struct ad7780_chip_info
> ad7780_chip_info_tbl[] = {
>  
>  static const struct iio_info ad7780_info = {
>  	.read_raw = ad7780_read_raw,
> +	.write_raw = ad7780_write_raw,
>  };
>  
>  static int ad7780_probe(struct spi_device *spi)
> @@ -222,6 +263,18 @@ static int ad7780_probe(struct spi_device *spi)
>  		goto error_disable_reg;
>  	}
>  
> +	if (st->chip_info->is_ad778x) {
> +		st->gain_gpio = devm_gpiod_get_optional(&spi->dev,
> +							"gain",
> +							GPIOD_OUT_HIGH);
> +		if (IS_ERR(st->gain_gpio)) {
> +			ret = PTR_ERR(st->gain_gpio);
> +			dev_err(&spi->dev, "Failed to request gain GPIO:
> %d\n",
> +				ret);
> +			goto error_disable_reg;
> +		}
> +	}
> +
>  	ret = ad_sd_setup_buffer_and_trigger(indio_dev);
>  	if (ret)
>  		goto error_disable_reg;
> diff --git a/include/linux/iio/adc/ad_sigma_delta.h
> b/include/linux/iio/adc/ad_sigma_delta.h
> index 730ead1a46df..6cadab6fd5fd 100644
> --- a/include/linux/iio/adc/ad_sigma_delta.h
> +++ b/include/linux/iio/adc/ad_sigma_delta.h
> @@ -173,6 +173,11 @@ int ad_sd_validate_trigger(struct iio_dev
> *indio_dev, struct iio_trigger *trig);
>  	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
>  		_storagebits, _shift, NULL, IIO_VOLTAGE, 0)
>  
> +#define AD_SD_CHANNEL_GAIN_FILTER(_si, _channel, _address, _bits, \
> +	_storagebits, _shift) \
> +	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> +		_storagebits, _shift, NULL, IIO_VOLTAGE,
> BIT(IIO_CHAN_INFO_RAW))
> +
>  #define AD_SD_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
>  	__AD_SD_CHANNEL(_si, 0, -1, _address, _bits, \
>  		_storagebits, _shift, NULL, IIO_TEMP, \

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Jonathan Cameron]

On Thu, 22 Nov 2018 11:01:00 +0000
"Popa, Stefan Serban" <StefanSerban.Popa@analog.com> wrote:

> On Mi, 2018-11-21 at 16:04 -0200, Giuliano Belinassi wrote:
> > Previously, the AD7780 driver only supported gpio for the 'powerdown'
> > pin. This commit adds suppport for the 'gain' and 'filter' pin.  
> Hey,
> 
> Comments inline.
> > 
> > Signed-off-by: Giuliano Belinassi <giuliano.belinassi@usp.br>
> > ---
> >  drivers/staging/iio/adc/ad7780.c       | 61 ++++++++++++++++++++++++--
> >  include/linux/iio/adc/ad_sigma_delta.h |  5 +++
> >  2 files changed, 62 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/staging/iio/adc/ad7780.c
> > b/drivers/staging/iio/adc/ad7780.c
> > index c4a85789c2db..69794f06dbcd 100644
> > --- a/drivers/staging/iio/adc/ad7780.c
> > +++ b/drivers/staging/iio/adc/ad7780.c
> > @@ -39,6 +39,9 @@
> >  #define AD7170_PATTERN		(AD7780_PAT0 | AD7170_PAT2)
> >  #define AD7170_PATTERN_MASK	(AD7780_PAT0 | AD7780_PAT1 |
> > AD7170_PAT2)
> >  
> > +#define AD7780_GAIN_GPIO	0
> > +#define AD7780_FILTER_GPIO	1
> > +
> >  struct ad7780_chip_info {
> >  	struct iio_chan_spec	channel;
> >  	unsigned int		pattern_mask;
> > @@ -50,6 +53,8 @@ struct ad7780_state {
> >  	const struct ad7780_chip_info	*chip_info;
> >  	struct regulator		*reg;
> >  	struct gpio_desc		*powerdown_gpio;
> > +	struct gpio_desc		*gain_gpio;
> > +	struct gpio_desc		*filter_gpio;
> >  	unsigned int	gain;
> >  
> >  	struct ad_sigma_delta sd;
> > @@ -115,18 +120,51 @@ static int ad7780_read_raw(struct iio_dev
> > *indio_dev,
> >  	return -EINVAL;
> >  }
> >  
> > +static int ad7780_write_raw(struct iio_dev *indio_dev,
> > +			    struct iio_chan_spec const *chan,
> > +			    int val,
> > +			    int val2,
> > +			    long m)
> > +{
> > +	struct ad7780_state *st = iio_priv(indio_dev);
> > +
> > +	if (m != IIO_CHAN_INFO_RAW)
> > +		return -EINVAL;
> > +
> > +	if (st->chip_info->is_ad778x) {
> > +		switch(val) {
> > +		case AD7780_GAIN_GPIO:  
> 
> I think that instead of setting the gain directly, we should use
> the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780 datasheet there
> is a formula from which the output code can be calculated:
> Code = 2^(N − 1)
> × [(AIN × Gain /VREF) + 1]. So, by setting the scale from user space, the
> driver can calculate the correct gain by using the formula above. Also, it
> would be useful to introduce scale available.
> Furthermore, there is a new
> ad7124 adc driver which does this exact thing. Take a look here: https://gi
> thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.c#L337.
> 
> > +			gpiod_set_value(st->gain_gpio, val2);
> > +		break;
> > +		case AD7780_FILTER_GPIO:  
> 
> The attribute that should be used to configure the filter gpio is
> IIO_CHAN_INFO_SAMP_FREQ. So, we should have 10 Hz and 16.7 Hz available
> sampling frequencies. If from user space the 10 Hz sampling freq is
> requested, then we set the FILTER pin high, while for 16.7 Hz the FILTER
> pin will be low.

Absolutely agreed with Stefan here.  If it had been decoupled from sampling
frequency (sometimes they are) then we have specific controls for filters
as well.  Here it directly effects the sampling frequency.

Please in future avoid any driver specific control like you have here.
I haven't really worked out what the interface is beyond some sort
of bitmap passed through a write to a magic channel?

If there isn't an existing interface in IIO for what you want to do
please propose one rather than doing something that will only work
with a particular userspace.  One of the primary purposes of having
a subsystem is to standardise interfaces.  This definitely doesn't
do that!

Will be good to have the support along the lines Stefan suggested though!

Thanks,

Jonathan



> 
> > +			gpiod_set_value(st->filter_gpio, val2);
> > +		break;
> > +		default:
> > +			return -EINVAL;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> >  static int ad7780_postprocess_sample(struct ad_sigma_delta *sigma_delta,
> >  				     unsigned int raw_sample)
> >  {
> >  	struct ad7780_state *st = ad_sigma_delta_to_ad7780(sigma_delta);
> >  	const struct ad7780_chip_info *chip_info = st->chip_info;
> > +	int val;
> >  
> >  	if ((raw_sample & AD7780_ERR) ||
> >  	    ((raw_sample & chip_info->pattern_mask) != chip_info-  
> > >pattern))  
> >  		return -EIO;
> >  
> >  	if (chip_info->is_ad778x) {
> > -		if (raw_sample & AD7780_GAIN)
> > +		val = raw_sample & AD7780_GAIN;
> > +
> > +		if (val != gpiod_get_value(st->gain_gpio))
> > +			return -EIO;
> > +
> > +		if (val)
> >  			st->gain = 1;
> >  		else
> >  			st->gain = 128;
> > @@ -141,18 +179,20 @@ static const struct ad_sigma_delta_info
> > ad7780_sigma_delta_info = {
> >  	.has_registers = false,
> >  };
> >  
> > -#define AD7780_CHANNEL(bits, wordsize) \
> > +#define AD7170_CHANNEL(bits, wordsize) \
> >  	AD_SD_CHANNEL_NO_SAMP_FREQ(1, 0, 0, bits, 32, wordsize - bits)
> > +#define AD7780_CHANNEL(bits, wordsize) \
> > +	AD_SD_CHANNEL_GAIN_FILTER(1, 0, 0, bits, 32, wordsize - bits)
> >  
> >  static const struct ad7780_chip_info ad7780_chip_info_tbl[] = {
> >  	[ID_AD7170] = {
> > -		.channel = AD7780_CHANNEL(12, 24),
> > +		.channel = AD7170_CHANNEL(12, 24),
> >  		.pattern = AD7170_PATTERN,
> >  		.pattern_mask = AD7170_PATTERN_MASK,
> >  		.is_ad778x = false,
> >  	},
> >  	[ID_AD7171] = {
> > -		.channel = AD7780_CHANNEL(16, 24),
> > +		.channel = AD7170_CHANNEL(16, 24),
> >  		.pattern = AD7170_PATTERN,
> >  		.pattern_mask = AD7170_PATTERN_MASK,
> >  		.is_ad778x = false,
> > @@ -173,6 +213,7 @@ static const struct ad7780_chip_info
> > ad7780_chip_info_tbl[] = {
> >  
> >  static const struct iio_info ad7780_info = {
> >  	.read_raw = ad7780_read_raw,
> > +	.write_raw = ad7780_write_raw,
> >  };
> >  
> >  static int ad7780_probe(struct spi_device *spi)
> > @@ -222,6 +263,18 @@ static int ad7780_probe(struct spi_device *spi)
> >  		goto error_disable_reg;
> >  	}
> >  
> > +	if (st->chip_info->is_ad778x) {
> > +		st->gain_gpio = devm_gpiod_get_optional(&spi->dev,
> > +							"gain",
> > +							GPIOD_OUT_HIGH);
> > +		if (IS_ERR(st->gain_gpio)) {
> > +			ret = PTR_ERR(st->gain_gpio);
> > +			dev_err(&spi->dev, "Failed to request gain GPIO:
> > %d\n",
> > +				ret);
> > +			goto error_disable_reg;
> > +		}
> > +	}
> > +
> >  	ret = ad_sd_setup_buffer_and_trigger(indio_dev);
> >  	if (ret)
> >  		goto error_disable_reg;
> > diff --git a/include/linux/iio/adc/ad_sigma_delta.h
> > b/include/linux/iio/adc/ad_sigma_delta.h
> > index 730ead1a46df..6cadab6fd5fd 100644
> > --- a/include/linux/iio/adc/ad_sigma_delta.h
> > +++ b/include/linux/iio/adc/ad_sigma_delta.h
> > @@ -173,6 +173,11 @@ int ad_sd_validate_trigger(struct iio_dev
> > *indio_dev, struct iio_trigger *trig);
> >  	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> >  		_storagebits, _shift, NULL, IIO_VOLTAGE, 0)
> >  
> > +#define AD_SD_CHANNEL_GAIN_FILTER(_si, _channel, _address, _bits, \
> > +	_storagebits, _shift) \
> > +	__AD_SD_CHANNEL(_si, _channel, -1, _address, _bits, \
> > +		_storagebits, _shift, NULL, IIO_VOLTAGE,
> > BIT(IIO_CHAN_INFO_RAW))
> > +
> >  #define AD_SD_TEMP_CHANNEL(_si, _address, _bits, _storagebits, _shift) \
> >  	__AD_SD_CHANNEL(_si, 0, -1, _address, _bits, \
> >  		_storagebits, _shift, NULL, IIO_TEMP,   

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Giuliano Belinassi]

Hi, thank you for the review

> On Thu, 22 Nov 2018 11:01:00 +0000
> "Popa, Stefan Serban" <StefanSerban.Popa@analog.com> wrote:
> > I think that instead of setting the gain directly, we should use
> > the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780 datasheet there
> > is a formula from which the output code can be calculated:
> > Code = 2^(N − 1)
> > × [(AIN × Gain /VREF) + 1]. So, by setting the scale from user space, the
> > driver can calculate the correct gain by using the formula above. Also, it
> > would be useful to introduce scale available.
> > Furthermore, there is a new
> > ad7124 adc driver which does this exact thing. Take a look here: https://gi
> > thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.c#L337.

We have some questions about the code you provided to us:
  1-) What is exactly the inputs for the write_raw function?
  2-) Could you give more details about the math around lines 346-348?
Is it correct to assume that the multiplication at line 346 won't
overflow? (vref is an uint)

And regarding our code:
  1-) The val in our write_raw function should be, in case of GAIN, a
number that best approximate the actual gain value of 1 or 128? For
instance, if the user inputs 126, we should default to 128?
  2-) In the case of FILTER, is it the same? Is the user sending the
value in mHz (milihertz)?

Thank you

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Popa, Stefan Serban]

On Lu, 2018-11-26 at 17:24 -0200, Giuliano Belinassi wrote:
Hi, please see bellow

> Hi, thank you for the review
> 
> > 
> > On Thu, 22 Nov 2018 11:01:00 +0000
> > "Popa, Stefan Serban" <StefanSerban.Popa@analog.com> wrote:
> > > 
> > > I think that instead of setting the gain directly, we should use
> > > the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780 datasheet
> > > there
> > > is a formula from which the output code can be calculated:
> > > Code = 2^(N − 1)
> > > × [(AIN × Gain /VREF) + 1]. So, by setting the scale from user space,
> > > the
> > > driver can calculate the correct gain by using the formula above.
> > > Also, it
> > > would be useful to introduce scale available.
> > > Furthermore, there is a new
> > > ad7124 adc driver which does this exact thing. Take a look here: http
> > > s://gi
> > > thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.c#
> > > L337.
> We have some questions about the code you provided to us:
>   1-) What is exactly the inputs for the write_raw function?

In your write_raw() function you need to add IIO_CHAN_INFO_SCALE case.
Setting the scale from user space looks something like this:
root:/sys/bus/iio/devices/iio:device0> echo 0.000298 > in_voltage_scale .
Furthermore, in your write_raw() function, val=0 and val2=298.
Knowing that full_scale_voltage = Vref / (gain * scale), we can calculate
the gain = Vref / (full_scale_voltage * scale). We only support two gains
(1 and 128), so we need to determine which one fits better with the desired
scale. Finally, all we have left to do is to set the gain. 
 
>   2-) Could you give more details about the math around lines 346-348?
> Is it correct to assume that the multiplication at line 346 won't
> overflow? (vref is an uint)

It is correct that Vref is in microvolts, so for example, Vref of 2.5V  =
2500000000uV. It won't overflow since we use the Vref as nominator, while
full_scale_voltage and scale are the denominators.

> 
> And regarding our code:
>   1-) The val in our write_raw function should be, in case of GAIN, a
> number that best approximate the actual gain value of 1 or 128? For
> instance, if the user inputs 126, we should default to 128?

We should not allow the the user to input the gain, he needs to input the
scale (see the mail from Jonathan and the above explanation). However, if
the calculated gain is one that is not supported, such as 126, we will set
the closest matching value, in this case 128.

>   2-) In the case of FILTER, is it the same? Is the user sending the
> value in mHz (milihertz)?

Yes, it is the same with the FILTER. You need to add
a IIO_CHAN_INFO_SAMP_FREQ case in your write_raw() function. From user
space, the input value should be in Hz, something like this:
root:/sys/bus/iio/devices/iio:device0> echo 10 >
in_voltage_sampling_frequency

> 
> Thank you
> 

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Ardelean, Alexandru]

On Tue, 2018-11-27 at 06:11 -0500, Popa, Stefan Serban wrote:
> On Lu, 2018-11-26 at 17:24 -0200, Giuliano Belinassi wrote:
> Hi, please see bellow
> 

One note from me here.

> > Hi, thank you for the review
> > 
> > > 
> > > On Thu, 22 Nov 2018 11:01:00 +0000
> > > "Popa, Stefan Serban" <StefanSerban.Popa@analog.com> wrote:
> > > > 
> > > > I think that instead of setting the gain directly, we should use
> > > > the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780
> > > > datasheet
> > > > there
> > > > is a formula from which the output code can be calculated:
> > > > Code = 2^(N − 1)
> > > > × [(AIN × Gain /VREF) + 1]. So, by setting the scale from user
> > > > space,
> > > > the
> > > > driver can calculate the correct gain by using the formula above.
> > > > Also, it
> > > > would be useful to introduce scale available.
> > > > Furthermore, there is a new
> > > > ad7124 adc driver which does this exact thing. Take a look here:
> > > > http
> > > > s://gi
> > > > thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.
> > > > c#
> > > > L337.
> > 
> > We have some questions about the code you provided to us:
> >   1-) What is exactly the inputs for the write_raw function?
> 
> In your write_raw() function you need to add IIO_CHAN_INFO_SCALE case.
> Setting the scale from user space looks something like this:
> root:/sys/bus/iio/devices/iio:device0> echo 0.000298 > in_voltage_scale .
> Furthermore, in your write_raw() function, val=0 and val2=298.
> Knowing that full_scale_voltage = Vref / (gain * scale), we can calculate
> the gain = Vref / (full_scale_voltage * scale). We only support two gains
> (1 and 128), so we need to determine which one fits better with the
> desired
> scale. Finally, all we have left to do is to set the gain. 
>  
> >   2-) Could you give more details about the math around lines 346-348?
> > Is it correct to assume that the multiplication at line 346 won't
> > overflow? (vref is an uint)
> 
> It is correct that Vref is in microvolts, so for example, Vref of 2.5V  =
> 2500000000uV. It won't overflow since we use the Vref as nominator, while
> full_scale_voltage and scale are the denominators.
> 

[Regarding the AD7124] I guess I should be noted that the code can
overflow, but in this case it shouldn't, because (according to the device
datasheet) the maximum VREF can be 3600 mV.
A user could specify (in the devicetree) something larger than 4300 mV (and
that would overflow) but that would also make the readings useless as the
external VREF would be invalid ; and there is also the risk of frying the
chip in that case [something you really can't protect the user against].

The internal VREF however is 2500 mV, so things should be fine from that
point of view.

Typically, in datasheets (at least from Analog Devices) it's good to take a
look at the specifications sections.
[For AD7124] You will see that the internal VREF [page 8] is 2.5V (with
approximation of +/-0.2%) and for external reference it goes all the way up
to AVDD, which has typical values of 2.9V - 3.6V.
So, for u32 this code should be fine and not overflow.

One small thing that can be confusing about that code in AD7124 is that it
gets multiplied with 1000000LL (which is signed long-long), but that should
be fine, since the operation should be converted to u32 (unsigned int)
representation [by being assigned to vref], which ends up being fine in the
end.

> > 
> > And regarding our code:
> >   1-) The val in our write_raw function should be, in case of GAIN, a
> > number that best approximate the actual gain value of 1 or 128? For
> > instance, if the user inputs 126, we should default to 128?
> 
> We should not allow the the user to input the gain, he needs to input the
> scale (see the mail from Jonathan and the above explanation). However, if
> the calculated gain is one that is not supported, such as 126, we will
> set
> the closest matching value, in this case 128.
> 
> >   2-) In the case of FILTER, is it the same? Is the user sending the
> > value in mHz (milihertz)?
> 
> Yes, it is the same with the FILTER. You need to add
> a IIO_CHAN_INFO_SAMP_FREQ case in your write_raw() function. From user
> space, the input value should be in Hz, something like this:
> root:/sys/bus/iio/devices/iio:device0> echo 10 >
> in_voltage_sampling_frequency
> 
> > 
> > Thank you

Re: [PATCH] staging: iio: ad7780: Add gain & filter gpio support

[Jonathan Cameron]

On Thu, 29 Nov 2018 12:19:08 +0000
"Ardelean, Alexandru" <alexandru.Ardelean@analog.com> wrote:

> On Tue, 2018-11-27 at 06:11 -0500, Popa, Stefan Serban wrote:
> > On Lu, 2018-11-26 at 17:24 -0200, Giuliano Belinassi wrote:
> > Hi, please see bellow
> >   
> 
> One note from me here.
> 
> > > Hi, thank you for the review
> > >   
> > > > 
> > > > On Thu, 22 Nov 2018 11:01:00 +0000
> > > > "Popa, Stefan Serban" <StefanSerban.Popa@analog.com> wrote:  
> > > > > 
> > > > > I think that instead of setting the gain directly, we should use
> > > > > the IIO_CHAN_INFO_SCALE attribute. At page 12 of the ad7780
> > > > > datasheet
> > > > > there
> > > > > is a formula from which the output code can be calculated:
> > > > > Code = 2^(N − 1)
> > > > > × [(AIN × Gain /VREF) + 1]. So, by setting the scale from user
> > > > > space,
> > > > > the
> > > > > driver can calculate the correct gain by using the formula above.
> > > > > Also, it
> > > > > would be useful to introduce scale available.
> > > > > Furthermore, there is a new
> > > > > ad7124 adc driver which does this exact thing. Take a look here:
> > > > > http
> > > > > s://gi
> > > > > thub.com/analogdevicesinc/linux/blob/master/drivers/iio/adc/ad7124.
> > > > > c#
> > > > > L337.  
> > > 
> > > We have some questions about the code you provided to us:
> > >   1-) What is exactly the inputs for the write_raw function?  
> > 
> > In your write_raw() function you need to add IIO_CHAN_INFO_SCALE case.
> > Setting the scale from user space looks something like this:  
> > root:/sys/bus/iio/devices/iio:device0> echo 0.000298 > in_voltage_scale .  
> > Furthermore, in your write_raw() function, val=0 and val2=298.
> > Knowing that full_scale_voltage = Vref / (gain * scale), we can calculate
> > the gain = Vref / (full_scale_voltage * scale). We only support two gains
> > (1 and 128), so we need to determine which one fits better with the
> > desired
> > scale. Finally, all we have left to do is to set the gain. 
> >    
> > >   2-) Could you give more details about the math around lines 346-348?
> > > Is it correct to assume that the multiplication at line 346 won't
> > > overflow? (vref is an uint)  
> > 
> > It is correct that Vref is in microvolts, so for example, Vref of 2.5V  =
> > 2500000000uV. It won't overflow since we use the Vref as nominator, while
> > full_scale_voltage and scale are the denominators.
> >   
> 
> [Regarding the AD7124] I guess I should be noted that the code can
> overflow, but in this case it shouldn't, because (according to the device
> datasheet) the maximum VREF can be 3600 mV.
> A user could specify (in the devicetree) something larger than 4300 mV (and
> that would overflow) but that would also make the readings useless as the
> external VREF would be invalid ; and there is also the risk of frying the
> chip in that case [something you really can't protect the user against].

Thanks Alex and Stefan for great detail here (glad you got to this before
I did ;)  One thing to add though is that if we have constraints like
this that would mess up the readings, it is sensible to check them
in the driver and at the very least put out a loud warning about the
problem, possibly even refuse to probe the driver.

The number of times I've spent hours chasing configuration problems
only to discover I was doing something stupid and the kernel silently
carried on regardlessly make me very keen on such commonsense protections.

I'm not going to review every driver to ensure they do this, but I'm keen
on them being checked where a possible problem has been identified!

Jonathan
> 
> The internal VREF however is 2500 mV, so things should be fine from that
> point of view.
> 
> Typically, in datasheets (at least from Analog Devices) it's good to take a
> look at the specifications sections.
> [For AD7124] You will see that the internal VREF [page 8] is 2.5V (with
> approximation of +/-0.2%) and for external reference it goes all the way up
> to AVDD, which has typical values of 2.9V - 3.6V.
> So, for u32 this code should be fine and not overflow.
> 
> One small thing that can be confusing about that code in AD7124 is that it
> gets multiplied with 1000000LL (which is signed long-long), but that should
> be fine, since the operation should be converted to u32 (unsigned int)
> representation [by being assigned to vref], which ends up being fine in the
> end.
> 
> > > 
> > > And regarding our code:
> > >   1-) The val in our write_raw function should be, in case of GAIN, a
> > > number that best approximate the actual gain value of 1 or 128? For
> > > instance, if the user inputs 126, we should default to 128?  
> > 
> > We should not allow the the user to input the gain, he needs to input the
> > scale (see the mail from Jonathan and the above explanation). However, if
> > the calculated gain is one that is not supported, such as 126, we will
> > set
> > the closest matching value, in this case 128.
> >   
> > >   2-) In the case of FILTER, is it the same? Is the user sending the
> > > value in mHz (milihertz)?  
> > 
> > Yes, it is the same with the FILTER. You need to add
> > a IIO_CHAN_INFO_SAMP_FREQ case in your write_raw() function. From user
> > space, the input value should be in Hz, something like this:  
> > root:/sys/bus/iio/devices/iio:device0> echo 10 >  
> > in_voltage_sampling_frequency
> >   
> > > 
> > > Thank you