linux-kernel - Re: [PATCH 2/2] iio: afe: unit-converter: add support for adi,lt6106

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Message-ID: <a70e8467-d0da-2b37-5dfa-7e14b388634c@ti.com>
Date:   Wed, 11 Apr 2018 10:43:07 -0500
From:   "Andrew F. Davis" <afd@...com>
To:     Peter Rosin <peda@...ntia.se>, <linux-kernel@...r.kernel.org>
CC:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Fabio Estevam <festevam@...il.com>,
        <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 2/2] iio: afe: unit-converter: add support for adi,lt6106

On 04/11/2018 09:15 AM, Peter Rosin wrote:
> This is a current sense amplifier from Analog Devices.
> 
> Signed-off-by: Peter Rosin <peda@...ntia.se>
> ---
>  drivers/iio/afe/Kconfig              |  3 +-
>  drivers/iio/afe/iio-unit-converter.c | 54 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 56 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/afe/Kconfig b/drivers/iio/afe/Kconfig
> index 642ce4eb12a6..0e10fe8f459a 100644
> --- a/drivers/iio/afe/Kconfig
> +++ b/drivers/iio/afe/Kconfig
> @@ -10,7 +10,8 @@ config IIO_UNIT_CONVERTER
>  	depends on OF || COMPILE_TEST
>  	help
>  	  Say yes here to build support for the IIO unit converter
> -	  that handles voltage dividers and current sense shunts.
> +	  that handles voltage dividers, current sense shunts and
> +	  the LT6106 Current Sense Amplifier from Analog Devices.

Could work better to split these out into separate drivers. Maybe a
iio-shunt-resistor.c that does just voltage->current with the
appropriate scaling. Then make a a separate lt6106.c.

"iio-unit-converter.c" isn't really doing what it says it is, it is not
a generic "unit converter" like one would assume. Having the driver name
describe what kind of device it physically represents will be better
when more complex AFEs show up that, for instance, have programmable
gains and need a larger driver.

Andrew

>  
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called iio-unit-converter.
> diff --git a/drivers/iio/afe/iio-unit-converter.c b/drivers/iio/afe/iio-unit-converter.c
> index fc50290d7e5e..4b0ae5ab9c2d 100644
> --- a/drivers/iio/afe/iio-unit-converter.c
> +++ b/drivers/iio/afe/iio-unit-converter.c
> @@ -144,6 +144,53 @@ static int unit_converter_configure_channel(struct device *dev,
>  	return 0;
>  }
>  
> +static int unit_converter_adi_lt6106_props(struct device *dev,
> +					   struct unit_converter *uc)
> +{
> +	u32 sense;
> +	u32 rin;
> +	u32 rout;
> +	u32 factor;
> +	int ret;
> +
> +	ret = device_property_read_u32(dev, "sense-resistor-micro-ohms",
> +				       &sense);
> +	if (ret) {
> +		dev_err(dev, "failed to read the sense resistance: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = device_property_read_u32(dev, "input-resistor-ohms", &rin);
> +	if (ret) {
> +		dev_err(dev, "failed to read the input resistance: %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = device_property_read_u32(dev, "output-resistor-ohms", &rout);
> +	if (ret) {
> +		dev_err(dev, "failed to read the output resistance: %d\n", ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * Calculate the scaling factor, rin / (rout * sense), while trying
> +	 * to keep the fraction from overflowing.
> +	 */
> +	factor = gcd(sense, 1000000);
> +	uc->numerator = 1000000 / factor;
> +	uc->denominator = sense / factor;
> +
> +	factor = gcd(uc->numerator, rout);
> +	uc->numerator /= factor;
> +	uc->denominator *= rout / factor;
> +
> +	factor = gcd(uc->denominator, rin);
> +	uc->numerator *= rin / factor;
> +	uc->denominator /= factor;
> +
> +	return 0;
> +}
> +
>  static int unit_converter_current_sense_shunt_props(struct device *dev,
>  						    struct unit_converter *uc)
>  {
> @@ -175,11 +222,16 @@ static int unit_converter_voltage_divider_props(struct device *dev,
>  }
>  
>  enum unit_converter_variant {
> +	ADI_LT6106,
>  	CURRENT_SENSE_SHUNT,
>  	VOLTAGE_DIVIDER,
>  };
>  
>  static const struct unit_converter_cfg unit_converter_cfg[] = {
> +	[ADI_LT6106] = {
> +		.type = IIO_CURRENT,
> +		.props = unit_converter_adi_lt6106_props,
> +	},
>  	[CURRENT_SENSE_SHUNT] = {
>  		.type = IIO_CURRENT,
>  		.props = unit_converter_current_sense_shunt_props,
> @@ -191,6 +243,8 @@ static const struct unit_converter_cfg unit_converter_cfg[] = {
>  };
>  
>  static const struct of_device_id unit_converter_match[] = {
> +	{ .compatible = "adi,lt6106",
> +	  .data = &unit_converter_cfg[ADI_LT6106], },
>  	{ .compatible = "current-sense-shunt",
>  	  .data = &unit_converter_cfg[CURRENT_SENSE_SHUNT], },
>  	{ .compatible = "voltage-divider",
>