linux-kernel - Re: [PATCH 6/6] iio: magnetometer: mmc35240: Add compensation for raw values

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Date:	Wed, 3 Jun 2015 10:42:36 +0200 (CEST)
From:	Peter Meerwald <pmeerw@...erw.net>
To:	Daniel Baluta <daniel.baluta@...el.com>
cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH 6/6] iio: magnetometer: mmc35240: Add compensation for
 raw values

On Wed, 3 Jun 2015, Daniel Baluta wrote:

> This patch adds compensation formula to raw readings, borrowed
> from Memsic's input driver.
> 
> Signed-off-by: Daniel Baluta <daniel.baluta@...el.com>
> ---
>  drivers/iio/magnetometer/mmc35240.c | 62 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 58 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iio/magnetometer/mmc35240.c b/drivers/iio/magnetometer/mmc35240.c
> index 88be660..902ad59 100644
> --- a/drivers/iio/magnetometer/mmc35240.c
> +++ b/drivers/iio/magnetometer/mmc35240.c
> @@ -58,6 +58,31 @@
>  #define MMC35240_WAIT_CHARGE_PUMP	50000	/* us */
>  #define MMC53240_WAIT_SET_RESET		1000	/* us */
>  
> +/*
> + * Memsic OTP process code piece is put here for reference:
> + *
> + * #define OTP_CONVERT(REG)  ((float)((REG) >=32 ? (32 - (REG)) : (REG)) * 0.006
> + * 1) For X axis, the COEFFICIENT is always 1.
> + * 2) For Y axis, the COEFFICIENT is as below:
> + *    f_OTP_matrix[4] = OTP_CONVERT(((reg_data[1] & 0x03) << 4) |
> + *                                   (reg_data[2] >> 4)) + 1.0;
> + * 3) For Z axis, the COEFFICIENT is as below:
> + *    f_OTP_matrix[8] = (OTP_CONVERT(reg_data[3] & 0x3f) + 1) * 1.35;
> + * We implemented the OTP logic into driver.
> + */
> +
> +/* scale = 1000 here for Y otp */
> +#define OTP_CONVERT_Y(REG)	(((REG) >= 32 ? (32 - (REG)) : (REG)) * 6)

MMC35240_ prefix

> +
> +/* 0.6 * 1.35 = 0.81, scale 10000 for Z otp */
> +#define OTP_CONVERT_Z(REG)	(((REG) >= 32 ? (32 - (REG)) : (REG)) * 81)
> +
> +#define X_COEFFICIENT(x)	(x)
> +#define Y_COEFFICIENT(y)	(y + 1000)
> +#define Z_COEFFICIENT(z)	(z + 13500)

prefix, maybe shorten to COEFF

> +
> +#define MMC35240_OTP_START_ADDR		0x1B
> +
>  enum mmc35240_resolution {
>  	MMC35240_16_BITS_SLOW = 0, /* 100 Hz */
>  	MMC35240_16_BITS_FAST,     /* 200 Hz */
> @@ -102,6 +127,10 @@ struct mmc35240_data {
>  	struct mutex mutex;
>  	struct regmap *regmap;
>  	enum mmc35240_resolution res;
> +
> +	/* OTP compensation */
> +	int axis_coef[3];
> +	int axis_scale[3];
>  };
>  
>  static const int mmc35240_samp_freq[] = {100, 200, 333, 666};
> @@ -172,8 +201,9 @@ static int mmc35240_hw_set(struct mmc35240_data *data, bool set)
>  
>  static int mmc35240_init(struct mmc35240_data *data)
>  {
> -	int ret;
> +	int ret, y_convert, z_convert;
>  	unsigned int reg_id;
> +	u8 otp_data[6];
>  
>  	ret = regmap_read(data->regmap, MMC35240_REG_ID, &reg_id);
>  	if (ret < 0) {
> @@ -197,9 +227,30 @@ static int mmc35240_init(struct mmc35240_data *data)
>  		return ret;
>  
>  	/* set default sampling frequency */
> -	return regmap_update_bits(data->regmap, MMC35240_REG_CTRL1,
> -				  MMC35240_CTRL1_BW_MASK,
> -				  data->res << MMC35240_CTRL1_BW_SHIFT);
> +	ret = regmap_update_bits(data->regmap, MMC35240_REG_CTRL1,
> +				 MMC35240_CTRL1_BW_MASK,
> +				 data->res << MMC35240_CTRL1_BW_SHIFT);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = regmap_bulk_read(data->regmap, MMC35240_OTP_START_ADDR,
> +			       (u8 *)otp_data, sizeof(otp_data));
> +	if (ret < 0)
> +		return ret;
> +
> +	y_convert = OTP_CONVERT_Y(((otp_data[1] & 0x03) << 4) |
> +				  (otp_data[2] >> 4));
> +	z_convert = OTP_CONVERT_Z(otp_data[3] & 0x3f);
> +
> +	data->axis_coef[0] = X_COEFFICIENT(1);
> +	data->axis_coef[1] = Y_COEFFICIENT(y_convert);
> +	data->axis_coef[2] = Z_COEFFICIENT(z_convert);
> +
> +	data->axis_scale[0] = 1;
> +	data->axis_scale[1] = 1000;
> +	data->axis_scale[2] = 10000;
> +
> +	return 0;
>  }
>  
>  static int mmc35240_take_measurement(struct mmc35240_data *data)
> @@ -286,6 +337,9 @@ static int mmc35240_raw_to_mgauss(struct mmc35240_data *data, int index,
>  	default:
>  		return -EINVAL;
>  	}
> +	/* apply OTP compensation */
> +	*val = (*val) * data->axis_coef[index] / data->axis_scale[index];
> +
>  	return 0;
>  }
>  
> 

-- 

Peter Meerwald
+43-664-2444418 (mobile)
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