iio: magnetometer: mmc35240: Add compensation for raw values

This patch adds compensation formula to raw readings, borrowed
from Memsic's input driver.

Signed-off-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

diff --git a/drivers/iio/magnetometer/mmc35240.c b/drivers/iio/magnetometer/mmc35240.c
index b2ab58ea15f015faa5f61439e51414f02a0e06b9..7a2ea71c659a0162baf0591af149045c36224d1b 100644 (file)
--- 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 MMC35240_OTP_CONVERT_Y(REG) (((REG) >= 32 ? (32 - (REG)) : (REG)) * 6)
+
+/* 0.6 * 1.35 = 0.81, scale 10000 for Z otp */
+#define MMC35240_OTP_CONVERT_Z(REG) (((REG) >= 32 ? (32 - (REG)) : (REG)) * 81)
+
+#define MMC35240_X_COEFF(x)    (x)
+#define MMC35240_Y_COEFF(y)    (y + 1000)
+#define MMC35240_Z_COEFF(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 = MMC35240_OTP_CONVERT_Y(((otp_data[1] & 0x03) << 4) |
+                                          (otp_data[2] >> 4));
+       z_convert = MMC35240_OTP_CONVERT_Z(otp_data[3] & 0x3f);
+
+       data->axis_coef[0] = MMC35240_X_COEFF(1);
+       data->axis_coef[1] = MMC35240_Y_COEFF(y_convert);
+       data->axis_coef[2] = MMC35240_Z_COEFF(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;
 }