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* [PATCH] iio: light: Simplify the current to lux LUT
@ 2020-02-20 21:20 Linus Walleij
  2020-02-21 13:17 ` Jonathan Cameron
  0 siblings, 1 reply; 2+ messages in thread
From: Linus Walleij @ 2020-02-20 21:20 UTC (permalink / raw)
  To: Jonathan Cameron, linux-iio
  Cc: Hartmut Knaack, Lars-Peter Clausen, Peter Meerwald-Stadler,
	linux-input, Gregor Riepl, Jonathan Bakker, Linus Walleij

From: Gregor Riepl <onitake@gmail.com>

The look-up-table for currens to lux is simply specifying
all currents from 5..47 mA, if we add some values for 0..5
we can just select the index for the lux value in an array
from the mA value. Use clamp() to get the value in the
range of values in the array.

Cc: Jonathan Bakker <xc-racer2@live.ca>
Signed-off-by: Gregor Riepl <onitake@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 drivers/iio/light/gp2ap002.c | 92 ++++++------------------------------
 1 file changed, 14 insertions(+), 78 deletions(-)

diff --git a/drivers/iio/light/gp2ap002.c b/drivers/iio/light/gp2ap002.c
index f747a42882e0..b24f43f961c8 100644
--- a/drivers/iio/light/gp2ap002.c
+++ b/drivers/iio/light/gp2ap002.c
@@ -204,71 +204,27 @@ static irqreturn_t gp2ap002_prox_irq(int irq, void *d)
 	return IRQ_HANDLED;
 }
 
-struct gp2ap002_illuminance {
-	unsigned int curr;
-	unsigned int lux;
-};
-
 /*
  * This array maps current and lux.
  *
  * Ambient light sensing range is 3 to 55000 lux.
  *
  * This mapping is based on the following formula.
- * illuminance = 10 ^ (current / 10)
+ * illuminance = 10 ^ (current[mA] / 10)
+ *
+ * When the ADC measures 0, return 0 lux.
  */
-static const struct gp2ap002_illuminance gp2ap002_illuminance_table[] = {
-	{ .curr		= 5, .lux	= 3 },
-	{ .curr		= 6, .lux	= 4 },
-	{ .curr		= 7, .lux	= 5 },
-	{ .curr		= 8, .lux	= 6 },
-	{ .curr		= 9, .lux	= 8 },
-	{ .curr		= 10, .lux	= 10 },
-	{ .curr		= 11, .lux	= 12 },
-	{ .curr		= 12, .lux	= 16 },
-	{ .curr		= 13, .lux	= 20 },
-	{ .curr		= 14, .lux	= 25 },
-	{ .curr		= 15, .lux	= 32 },
-	{ .curr		= 16, .lux	= 40 },
-	{ .curr		= 17, .lux	= 50 },
-	{ .curr		= 18, .lux	= 63 },
-	{ .curr		= 19, .lux	= 79 },
-	{ .curr		= 20, .lux	= 100 },
-	{ .curr		= 21, .lux	= 126 },
-	{ .curr		= 22, .lux	= 158 },
-	{ .curr		= 23, .lux	= 200 },
-	{ .curr		= 24, .lux	= 251 },
-	{ .curr		= 25, .lux	= 316 },
-	{ .curr		= 26, .lux	= 398 },
-	{ .curr		= 27, .lux	= 501 },
-	{ .curr		= 28, .lux	= 631 },
-	{ .curr		= 29, .lux	= 794 },
-	{ .curr		= 30, .lux	= 1000 },
-	{ .curr		= 31, .lux	= 1259 },
-	{ .curr		= 32, .lux	= 1585 },
-	{ .curr		= 33, .lux	= 1995 },
-	{ .curr		= 34, .lux	= 2512 },
-	{ .curr		= 35, .lux	= 3162 },
-	{ .curr		= 36, .lux	= 3981 },
-	{ .curr		= 37, .lux	= 5012 },
-	{ .curr		= 38, .lux	= 6310 },
-	{ .curr		= 39, .lux	= 7943 },
-	{ .curr		= 40, .lux	= 10000 },
-	{ .curr		= 41, .lux	= 12589 },
-	{ .curr		= 42, .lux	= 15849 },
-	{ .curr		= 43, .lux	= 19953 },
-	{ .curr		= 44, .lux	= 25119 },
-	{ .curr		= 45, .lux	= 31623 },
-	{ .curr		= 46, .lux	= 39811 },
-	{ .curr		= 47, .lux	= 50119 },
+static const u16 gp2ap002_illuminance_table[] = {
+	0, 1, 1, 2, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, 25, 32, 40, 50, 63, 79,
+	100, 126, 158, 200, 251, 316, 398, 501, 631, 794, 1000, 1259, 1585,
+	1995, 2512, 3162, 3981, 5012, 6310, 7943, 10000, 12589, 15849, 19953,
+	25119, 31623, 39811, 50119,
 };
 
 static int gp2ap002_get_lux(struct gp2ap002 *gp2ap002)
 {
-	const struct gp2ap002_illuminance *ill1;
-	const struct gp2ap002_illuminance *ill2;
 	int ret, res;
-	int i;
+	u16 lux;
 
 	ret = iio_read_channel_processed(gp2ap002->alsout, &res);
 	if (ret < 0)
@@ -276,31 +232,11 @@ static int gp2ap002_get_lux(struct gp2ap002 *gp2ap002)
 
 	dev_dbg(gp2ap002->dev, "read %d mA from ADC\n", res);
 
-	ill1 = &gp2ap002_illuminance_table[0];
-	if (res < ill1->curr) {
-		dev_dbg(gp2ap002->dev, "total darkness\n");
-		return 0;
-	}
-	for (i = 0; i < ARRAY_SIZE(gp2ap002_illuminance_table) - 1; i++) {
-		ill1 = &gp2ap002_illuminance_table[i];
-		ill2 = &gp2ap002_illuminance_table[i + 1];
-
-		if (res > ill2->curr)
-			continue;
-		if ((res <= ill1->curr) && (res >= ill2->curr))
-			break;
-	}
-	if (res > ill2->curr) {
-		dev_info_once(gp2ap002->dev, "max current overflow\n");
-		return ill2->curr;
-	}
-	/* Interpolate and return */
-	dev_dbg(gp2ap002->dev, "interpolate index %d and %d\n", i, i + 1);
-	/* How many steps along the curve */
-	i = res - ill1->curr; /* x - x0 */
-	/* Linear interpolation */
-	return ill1->lux + i *
-		((ill2->lux - ill1->lux) / (ill2->curr - ill1->curr));
+	/* ensure we don't under/overflow */
+	res = clamp(res, 0, (int)ARRAY_SIZE(gp2ap002_illuminance_table) - 1);
+	lux = gp2ap002_illuminance_table[res];
+
+	return (int)lux;
 }
 
 static int gp2ap002_read_raw(struct iio_dev *indio_dev,
-- 
2.21.1


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2020-02-20 21:20 [PATCH] iio: light: Simplify the current to lux LUT Linus Walleij
2020-02-21 13:17 ` Jonathan Cameron

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