Re: [PATCH v2 7/7] iio: imu: fxos8700: fix MAGN sensor scale and unit

From: Jonathan Cameron <jic23@kernel.org>
To: carlos.song@nxp.com
Cc: lars@metafoo.de, rjones@gateworks.com,
	Jonathan.Cameron@huawei.com, haibo.chen@nxp.com,
	linux-imx@nxp.com, linux-iio@vger.kernel.org
Subject: Re: [PATCH v2 7/7] iio: imu: fxos8700: fix MAGN sensor scale and unit
Date: Sun, 11 Dec 2022 14:05:30 +0000	[thread overview]
Message-ID: <20221211140530.158924a4@jic23-huawei> (raw)
In-Reply-To: <20221208071911.2405922-8-carlos.song@nxp.com>

On Thu,  8 Dec 2022 15:19:11 +0800
carlos.song@nxp.com wrote:

> From: Carlos Song <carlos.song@nxp.com>
> 
> +/-1200uT is a MAGN sensor full measurement range. Magnetometer scale
> is the magnetic sensitivity parameter. It is referenced as 0.1uT
> according to datasheet and magnetometer channel unit is Gauss in
> sysfs-bus-iio documentation. Gauss and uTesla unit conversion
> relationship as follows: 0.1uT = 0.001g.
> 
> Set magnetometer scale and available magnetometer scale as fixed 0.001g.
> 
> Fixes: 84e5ddd5c46e ("iio: imu: Add support for the FXOS8700 IMU")
> Signed-off-by: Carlos Song <carlos.song@nxp.com>
> ---
> Changes for V2:
> - Modify the magnetometer sensitivity unit to be consistent with the
>   documentation as 0.001g
> - Rework commit log
> 
> diff --git a/drivers/iio/imu/fxos8700_core.c b/drivers/iio/imu/fxos8700_core.c
> index b4baef82f6d5..1780ed99d2f9 100644
> --- a/drivers/iio/imu/fxos8700_core.c
> +++ b/drivers/iio/imu/fxos8700_core.c
> @@ -352,7 +352,7 @@ static int fxos8700_set_scale(struct fxos8700_data *data,
>  	struct device *dev = regmap_get_device(data->regmap);
>  
>  	if (t == FXOS8700_MAGN) {
> -		dev_err(dev, "Magnetometer scale is locked at 1200uT\n");
> +		dev_err(dev, "Magnetometer scale is locked at 0.001g\n");

Gauss unit (according to wikipedia) is G or Gs

>  		return -EINVAL;
>  	}
>  
> @@ -397,7 +397,7 @@ static int fxos8700_get_scale(struct fxos8700_data *data,
>  	static const int scale_num = ARRAY_SIZE(fxos8700_accel_scale);
>  
>  	if (t == FXOS8700_MAGN) {
> -		*uscale = 1200; /* Magnetometer is locked at 1200uT */
> +		*uscale = 1000; /* Magnetometer is locked at 0.001g */
>  		return 0;
>  	}
>  
> @@ -591,7 +591,7 @@ static IIO_CONST_ATTR(in_accel_sampling_frequency_available,
>  static IIO_CONST_ATTR(in_magn_sampling_frequency_available,
>  		      "1.5625 6.25 12.5 50 100 200 400 800");
>  static IIO_CONST_ATTR(in_accel_scale_available, "0.000244 0.000488 0.000976");
> -static IIO_CONST_ATTR(in_magn_scale_available, "0.000001200");
> +static IIO_CONST_ATTR(in_magn_scale_available, "0.001000");

Check that against what you get reading the value.  If it is 0.001Gs then
this is right, but the uscale above isn't. (that is 0.0001Gs)

>  
>  static struct attribute *fxos8700_attrs[] = {
>  	&iio_const_attr_in_accel_sampling_frequency_available.dev_attr.attr,