[PATCH v2 6/7] bu27034: ROHM BU27034ANUC correct lux calculation

Matti Vaittinen
2024-07-05T10:55:41Z

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The ROHM BU27034NUC was cancelled and BU27034ANUC is replacing this
sensor. The lux computation based on the data from a BU27034ANUC is
different from the computation for the data from an old BU27034NUC.

Fix the lux computation.

Signed-off-by: Matti Vaittinen <mazziesaccount@gmail.com>
---
Revision history:
v1 => v2:
- splitted from a big patch
- fix maths in comments to follow the coding style
- fix the D1 / D0 ratio logic when picking the right coefficients for
Lux calculation
---
drivers/iio/light/rohm-bu27034.c | 157 ++++++-------------------------
1 file changed, 31 insertions(+), 126 deletions(-)

diff --git a/drivers/iio/light/rohm-bu27034.c b/drivers/iio/light/rohm-bu27034.c
index 850ec78f5405..ec4f9bef83f8 100644
--- a/drivers/iio/light/rohm-bu27034.c
+++ b/drivers/iio/light/rohm-bu27034.c
@@ -573,102 +573,21 @@ static int bu27034_set_scale(struct bu27034_data *data, int chan,
}

/*
- * for (D1/D0 < 0.87):
- * lx = 0.004521097 * D1 - 0.002663996 * D0 +
- * 0.00012213 * D1 * D1 / D0
+ * for (D1/D0 < 1.5):
+ * lx = (0.001193 * D0 + (-0.0000747) * D1) * ((D1/D0 – 1.5) * (0.25) + 1)
*
- * => 115.7400832 * ch1 / gain1 / mt -
- * 68.1982976 * ch0 / gain0 / mt +
- * 0.00012213 * 25600 * (ch1 / gain1 / mt) * 25600 *
- * (ch1 /gain1 / mt) / (25600 * ch0 / gain0 / mt)
+ * => -0.000745625 * D0 + 0.0002515625 * D1 + -0.000018675 * D1 * D1 / D0
*
- * A = 0.00012213 * 25600 * (ch1 /gain1 / mt) * 25600 *
- * (ch1 /gain1 / mt) / (25600 * ch0 / gain0 / mt)
- * => 0.00012213 * 25600 * (ch1 /gain1 / mt) *
- * (ch1 /gain1 / mt) / (ch0 / gain0 / mt)
- * => 0.00012213 * 25600 * (ch1 / gain1) * (ch1 /gain1 / mt) /
- * (ch0 / gain0)
- * => 0.00012213 * 25600 * (ch1 / gain1) * (ch1 /gain1 / mt) *
- * gain0 / ch0
- * => 3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / mt /ch0
+ * => (6.44 * ch1 / gain1 + 19.088 * ch0 / gain0 -
+ * 0.47808 * ch1 * ch1 * gain0 / gain1 / gain1 / ch0) /
+ * mt
*
- * lx = (115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0) /
- * mt + A
- * => (115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0) /
- * mt + 3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / mt /
- * ch0
+ * Else
+ * lx = 0.001193 * D0 - 0.0000747 * D1
*
- * => (115.7400832 * ch1 / gain1 - 68.1982976 * ch0 / gain0 +
- * 3.126528 * ch1 * ch1 * gain0 / gain1 / gain1 / ch0) /
- * mt
- *
- * For (0.87 <= D1/D0 < 1.00)
- * lx = (0.001331* D0 + 0.0000354 * D1) * ((D1/D0 – 0.87) * (0.385) + 1)
- * => (0.001331 * 256 * 100 * ch0 / gain0 / mt + 0.0000354 * 256 *
- * 100 * ch1 / gain1 / mt) * ((D1/D0 - 0.87) * (0.385) + 1)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * ((D1/D0 - 0.87) * (0.385) + 1)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * (0.385 * D1/D0 - 0.66505)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * (0.385 * 256 * 100 * ch1 / gain1 / mt / (256 * 100 * ch0 / gain0 / mt) - 0.66505)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * (9856 * ch1 / gain1 / mt / (25600 * ch0 / gain0 / mt) + 0.66505)
- * => 13.118336 * ch1 / (gain1 * mt)
- * + 22.66064768 * ch0 / (gain0 * mt)
- * + 8931.90144 * ch1 * ch1 * gain0 /
- * (25600 * ch0 * gain1 * gain1 * mt)
- * + 0.602694912 * ch1 / (gain1 * mt)
- *
- * => [0.3489024 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1)
- * + 22.66064768 * ch0 / gain0
- * + 13.721030912 * ch1 / gain1
- * ] / mt
- *
- * For (D1/D0 >= 1.00)
- *
- * lx = (0.001331* D0 + 0.0000354 * D1) * ((D1/D0 – 2.0) * (-0.05) + 1)
- * => (0.001331* D0 + 0.0000354 * D1) * (-0.05D1/D0 + 1.1)
- * => (0.001331 * 256 * 100 * ch0 / gain0 / mt + 0.0000354 * 256 *
- * 100 * ch1 / gain1 / mt) * (-0.05D1/D0 + 1.1)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * (-0.05 * 256 * 100 * ch1 / gain1 / mt / (256 * 100 * ch0 / gain0 / mt) + 1.1)
- * => (34.0736 * ch0 / gain0 / mt + 0.90624 * ch1 / gain1 / mt) *
- * (-1280 * ch1 / (gain1 * mt * 25600 * ch0 / gain0 / mt) + 1.1)
- * => (34.0736 * ch0 * -1280 * ch1 * gain0 * mt /( gain0 * mt * gain1 * mt * 25600 * ch0)
- * + 34.0736 * 1.1 * ch0 / (gain0 * mt)
- * + 0.90624 * ch1 * -1280 * ch1 *gain0 * mt / (gain1 * mt *gain1 * mt * 25600 * ch0)
- * + 1.1 * 0.90624 * ch1 / (gain1 * mt)
- * => -43614.208 * ch1 / (gain1 * mt * 25600)
- * + 37.48096 ch0 / (gain0 * mt)
- * - 1159.9872 * ch1 * ch1 * gain0 / (gain1 * gain1 * mt * 25600 * ch0)
- * + 0.996864 ch1 / (gain1 * mt)
- * => [
- * - 0.045312 * ch1 * ch1 * gain0 / (gain1 * gain1 * ch0)
- * - 0.706816 * ch1 / gain1
- * + 37.48096 ch0 /gain0
- * ] * mt
- *
- *
- * So, the first case (D1/D0 < 0.87) can be computed to a form:
- *
- * lx = (3.126528 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
- * 115.7400832 * ch1 / gain1 +
- * -68.1982976 * ch0 / gain0
- * / mt
- *
- * Second case (0.87 <= D1/D0 < 1.00) goes to form:
- *
- * => [0.3489024 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
- * 13.721030912 * ch1 / gain1 +
- * 22.66064768 * ch0 / gain0
- * ] / mt
- *
- * Third case (D1/D0 >= 1.00) goes to form:
- * => [-0.045312 * ch1 * ch1 * gain0 / (ch0 * gain1 * gain1) +
- * -0.706816 * ch1 / gain1 +
- * 37.48096 ch0 /(gain0
- * ] / mt
+ * => (1.91232 * ch1 / gain1 + 30.5408 * ch0 / gain0 +
+ * [0 * ch1 * ch1 * gain0 / gain1 / gain1 / ch0] ) /
+ * mt
*
* This can be unified to format:
* lx = [
@@ -678,19 +597,14 @@ static int bu27034_set_scale(struct bu27034_data *data, int chan,
* ] / mt
*
* For case 1:
- * A = 3.126528,
- * B = 115.7400832
- * C = -68.1982976
+ * A = -0.47808,
+ * B = 6.44,
+ * C = 19.088
*
* For case 2:
- * A = 0.3489024
- * B = 13.721030912
- * C = 22.66064768
- *
- * For case 3:
- * A = -0.045312
- * B = -0.706816
- * C = 37.48096
+ * A = 0
+ * B = 1.91232
+ * C = 30.5408
*/

struct bu27034_lx_coeff {
@@ -795,21 +709,16 @@ static int bu27034_fixp_calc_lx(unsigned int ch0, unsigned int ch1,
{
static const struct bu27034_lx_coeff coeff[] = {
{
- .A = 31265280, /* 3.126528 */
- .B = 1157400832, /*115.7400832 */
- .C = 681982976, /* -68.1982976 */
- .is_neg = {false, false, true},
+ .A = 4780800, /* -0.47808 */
+ .B = 64400000, /* 6.44 */
+ .C = 190880000, /* 19.088 */
+ .is_neg = { true, false, false },
}, {
- .A = 3489024, /* 0.3489024 */
- .B = 137210309, /* 13.721030912 */
- .C = 226606476, /* 22.66064768 */
+ .A = 0, /* 0 */
+ .B = 19123200, /* 1.91232 */
+ .C = 305408000, /* 30.5408 */
/* All terms positive */
- }, {
- .A = 453120, /* -0.045312 */
- .B = 7068160, /* -0.706816 */
- .C = 374809600, /* 37.48096 */
- .is_neg = {true, true, false},
- }
+ },
};
const struct bu27034_lx_coeff *c = &coeff[coeff_idx];
u64 res = 0, terms[3];
@@ -972,12 +881,10 @@ static int bu27034_get_single_result(struct bu27034_data *data, int chan,
* D1 = data1/ch1_gain/meas_time_ms * 25600
*
* Then:
- * if (D1/D0 < 0.87)
- * lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 0.87) * 3.45 + 1)
- * else if (D1/D0 < 1)
- * lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 0.87) * 0.385 + 1)
- * else
- * lx = (0.001331 * D0 + 0.0000354 * D1) * ((D1 / D0 - 2) * -0.05 + 1)
+ * If (D1/D0 < 1.5)
+ * lx = (0.001193 * D0 + (-0.0000747) * D1) * ((D1 / D0 – 1.5) * 0.25 + 1)
+ * Else
+ * lx = (0.001193 * D0 + (-0.0000747) * D1)
*
* We use it here. Users who have for example some colored lens
* need to modify the calculation but I hope this gives a starting point for
@@ -1028,12 +935,10 @@ static int bu27034_calc_mlux(struct bu27034_data *data, __le16 *res, int *val)
d1_d0_ratio_scaled /= ch0 * gain1;
}

- if (d1_d0_ratio_scaled < 87)
+ if (d1_d0_ratio_scaled < 150)
ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 0);
- else if (d1_d0_ratio_scaled < 100)
- ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 1);
else
- ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 2);
+ ret = bu27034_fixp_calc_lx(ch0, ch1, gain0, gain1, meastime, 1);

if (ret < 0)
return ret;