Re: [PATCH v5 3/5] iio: adc: ad7949: add support for internal vref

[Jonathan Cameron <jic23@kernel.org>]

On Sat,  7 Aug 2021 21:56:57 -0400
Liam Beguin <liambeguin@gmail.com> wrote:

> From: Liam Beguin <lvb@xiphos.com>
> 
> Add support for selecting a custom reference voltage from the
> devicetree. If an external source is used, a vref regulator should be
> defined in the devicetree.
> 
> Signed-off-by: Liam Beguin <lvb@xiphos.com>

Hi Liam, I'm not sure the parsing of the child nodes will work if using
an external reference. See below.

Jonathan

> ---
>  drivers/iio/adc/ad7949.c | 140 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 122 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> index 3f94ae639a44..14a7c79d637e 100644
> --- a/drivers/iio/adc/ad7949.c
> +++ b/drivers/iio/adc/ad7949.c
> @@ -35,7 +35,11 @@
>  
>  /* REF: reference/buffer selection */
>  #define AD7949_CFG_BIT_REF		GENMASK(5, 3)
> -#define AD7949_CFG_VAL_REF_EXT_BUF		7
> +#define AD7949_CFG_VAL_REF_EXT_TEMP_BUF		3
> +#define AD7949_CFG_VAL_REF_EXT_TEMP		2
> +#define AD7949_CFG_VAL_REF_INT_4096		1
> +#define AD7949_CFG_VAL_REF_INT_2500		0
> +#define AD7949_CFG_VAL_REF_EXTERNAL		BIT(1)
>  
>  /* SEQ: channel sequencer. Allows for scanning channels */
>  #define AD7949_CFG_BIT_SEQ		GENMASK(2, 1)
> @@ -60,6 +64,14 @@ static const struct ad7949_adc_spec ad7949_adc_spec[] = {
>  	[ID_AD7689] = { .num_channels = 8, .resolution = 16 },
>  };
>  
> +/**
> + * struct ad7949_channel - ADC Channel parameters
> + * @refsel: reference selection
> + */
> +struct ad7949_channel {
> +	u32 refsel;
> +};
> +
>  /**
>   * struct ad7949_adc_chip - AD ADC chip
>   * @lock: protects write sequences
> @@ -78,6 +90,7 @@ struct ad7949_adc_chip {
>  	struct regulator *vref;
>  	struct iio_dev *indio_dev;
>  	struct spi_device *spi;
> +	struct ad7949_channel *channels;
>  	u8 resolution;
>  	u8 bits_per_word;
>  	u16 cfg;
> @@ -136,6 +149,7 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
>  	int ret;
>  	int i;
>  	struct spi_message msg;
> +	struct ad7949_channel *ad7949_chan = &ad7949_adc->channels[channel];
>  	struct spi_transfer tx[] = {
>  		{
>  			.len = 2,
> @@ -156,8 +170,9 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
>  	 */
>  	for (i = 0; i < 2; i++) {
>  		ret = ad7949_spi_write_cfg(ad7949_adc,
> -					   FIELD_PREP(AD7949_CFG_BIT_INX, channel),
> -					   AD7949_CFG_BIT_INX);
> +					   FIELD_PREP(AD7949_CFG_BIT_INX, channel) |
> +					   FIELD_PREP(AD7949_CFG_BIT_REF, ad7949_chan->refsel),
> +					   AD7949_CFG_BIT_INX | AD7949_CFG_BIT_REF);
>  		if (ret)
>  			return ret;
>  		if (channel == ad7949_adc->current_channel)
> @@ -225,6 +240,7 @@ static int ad7949_spi_read_raw(struct iio_dev *indio_dev,
>  			   int *val, int *val2, long mask)
>  {
>  	struct ad7949_adc_chip *ad7949_adc = iio_priv(indio_dev);
> +	struct ad7949_channel *ad7949_chan = &ad7949_adc->channels[chan->channel];
>  	int ret;
>  
>  	if (!val)
> @@ -242,12 +258,26 @@ static int ad7949_spi_read_raw(struct iio_dev *indio_dev,
>  		return IIO_VAL_INT;
>  
>  	case IIO_CHAN_INFO_SCALE:
> -		ret = regulator_get_voltage(ad7949_adc->vref);
> -		if (ret < 0)
> -			return ret;
> +		switch (ad7949_chan->refsel) {
> +		case AD7949_CFG_VAL_REF_INT_2500:
> +			*val = 2500;
> +			break;
> +		case AD7949_CFG_VAL_REF_INT_4096:
> +			*val = 4096;
> +			break;
> +		case AD7949_CFG_VAL_REF_EXT_TEMP:
> +		case AD7949_CFG_VAL_REF_EXT_TEMP_BUF:
> +			ret = regulator_get_voltage(ad7949_adc->vref);
> +			if (ret < 0)
> +				return ret;
> +
> +			/* convert value back to mV */
> +			*val = ret / 1000;
> +			break;
> +		}
>  
> -		*val = ret / 5000;
> -		return IIO_VAL_INT;
> +		*val2 = (1 << ad7949_adc->resolution) - 1;
> +		return IIO_VAL_FRACTIONAL;
>  	}
>  
>  	return -EINVAL;
> @@ -286,7 +316,7 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
>  		FIELD_PREP(AD7949_CFG_BIT_INCC, AD7949_CFG_VAL_INCC_UNIPOLAR_GND) |
>  		FIELD_PREP(AD7949_CFG_BIT_INX, ad7949_adc->current_channel) |
>  		FIELD_PREP(AD7949_CFG_BIT_BW_FULL, 1) |
> -		FIELD_PREP(AD7949_CFG_BIT_REF, AD7949_CFG_VAL_REF_EXT_BUF) |
> +		FIELD_PREP(AD7949_CFG_BIT_REF, ad7949_adc->channels[0].refsel) |
>  		FIELD_PREP(AD7949_CFG_BIT_SEQ, 0x0) |
>  		FIELD_PREP(AD7949_CFG_BIT_RBN, 1);
>  
> @@ -302,14 +332,24 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
>  	return ret;
>  }
>  
> +static void ad7949_disable_reg(void *reg)
> +{
> +	regulator_disable(reg);
> +}
> +
>  static int ad7949_spi_probe(struct spi_device *spi)
>  {
>  	u32 spi_ctrl_mask = spi->controller->bits_per_word_mask;
>  	struct device *dev = &spi->dev;
>  	const struct ad7949_adc_spec *spec;
>  	struct ad7949_adc_chip *ad7949_adc;
> +	struct ad7949_channel *ad7949_chan;
> +	struct fwnode_handle *child;
>  	struct iio_dev *indio_dev;
> +	int mode;
> +	u32 tmp;
>  	int ret;
> +	int i;
>  
>  	indio_dev = devm_iio_device_alloc(dev, sizeof(*ad7949_adc));
>  	if (!indio_dev) {
> @@ -343,16 +383,82 @@ static int ad7949_spi_probe(struct spi_device *spi)
>  		return -EINVAL;
>  	}
>  
> -	ad7949_adc->vref = devm_regulator_get(dev, "vref");
> +	/* Setup external voltage ref, buffered? */
> +	ad7949_adc->vref = devm_regulator_get_optional(dev, "vrefin");
>  	if (IS_ERR(ad7949_adc->vref)) {
> -		dev_err(dev, "fail to request regulator\n");
> -		return PTR_ERR(ad7949_adc->vref);
> +		ret = PTR_ERR(ad7949_adc->vref);
> +		if (ret != -ENODEV)
> +			return ret;
> +		/* unbuffered? */
> +		ad7949_adc->vref = devm_regulator_get_optional(dev, "vref");
> +		if (IS_ERR(ad7949_adc->vref)) {
> +			ret = PTR_ERR(ad7949_adc->vref);
> +			if (ret != -ENODEV)
> +				return ret;
> +			/* Internal then */
> +			mode = AD7949_CFG_VAL_REF_INT_4096;
> +		} else {
> +			mode = AD7949_CFG_VAL_REF_EXT_TEMP;
> +		}
> +	} else {
> +		mode = AD7949_CFG_VAL_REF_EXT_TEMP_BUF;
>  	}
>  
> -	ret = regulator_enable(ad7949_adc->vref);
> -	if (ret < 0) {
> -		dev_err(dev, "fail to enable regulator\n");
> -		return ret;
> +	if (mode & AD7949_CFG_VAL_REF_EXTERNAL) {
> +		ret = regulator_enable(ad7949_adc->vref);
> +		if (ret < 0) {
> +			dev_err(dev, "fail to enable regulator\n");
> +			return ret;
> +		}
> +
> +		ret = devm_add_action_or_reset(dev, ad7949_disable_reg,
> +					       ad7949_adc->vref);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	ad7949_adc->channels = devm_kcalloc(dev, spec->num_channels,
> +					    sizeof(*ad7949_adc->channels),
> +					    GFP_KERNEL);
> +	if (!ad7949_adc->channels) {
> +		dev_err(dev, "unable to allocate ADC channels\n");
> +		return -ENOMEM;
> +	}
> +
> +	/* Initialize all channel structures */
> +	for (i = 0; i < spec->num_channels; i++)
> +		ad7949_adc->channels[i].refsel = mode;
> +
> +	/* Read channel specific information form the devicetree */
> +	device_for_each_child_node(dev, child) {
> +		ret = fwnode_property_read_u32(child, "reg", &i);
> +		if (ret) {
> +			dev_err(dev, "missing reg property in %pfw\n", child);
> +			fwnode_handle_put(child);
> +			return ret;
> +		}
> +
> +		ad7949_chan = &ad7949_adc->channels[i];
> +
> +		ret = fwnode_property_read_u32(child, "adi,internal-ref-microvolt", &tmp);
> +		if (ret < 0 && ret != -EINVAL) {
> +			dev_err(dev, "invalid internal reference in %pfw\n", child);
> +			fwnode_handle_put(child);
> +			return ret;
> +		}

So if we are using external voltage, then we'd not expect this to exist. 
ret != -EINVAL should deal with that.  However, we then hit the following switch
and temp isn't set to an appropriate value so we get the error.

Am I missing something?

> +
> +		switch (tmp) {
> +		case 2500000:
> +			ad7949_chan->refsel = AD7949_CFG_VAL_REF_INT_2500;
> +			break;
> +		case 4096000:
> +			ad7949_chan->refsel = AD7949_CFG_VAL_REF_INT_4096;
> +			break;
> +		default:
> +			dev_err(dev, "unsupported internal voltage reference\n");
> +			fwnode_handle_put(child);
> +			return -EINVAL;
> +		}
>  	}
>  
>  	mutex_init(&ad7949_adc->lock);
> @@ -373,7 +479,6 @@ static int ad7949_spi_probe(struct spi_device *spi)
>  
>  err:
>  	mutex_destroy(&ad7949_adc->lock);
> -	regulator_disable(ad7949_adc->vref);
>  
>  	return ret;
>  }
> @@ -385,7 +490,6 @@ static int ad7949_spi_remove(struct spi_device *spi)
>  
>  	iio_device_unregister(indio_dev);
>  	mutex_destroy(&ad7949_adc->lock);
> -	regulator_disable(ad7949_adc->vref);
>  
>  	return 0;
>  }