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Subject[PATCH 6/6] iio: magnetometer: mmc35240: Add compensation for raw values
Date
This patch adds compensation formula to raw readings, borrowed
from Memsic's input driver.

Signed-off-by: Daniel Baluta <daniel.baluta@intel.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)
+
+/* 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)
+
+#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;
}

--
1.9.1


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