[PATCH 2/2] light sensor: Preserve granularity of amplified tsl2583 light sensor values.

[Bryan Freed <bfreed@chromium.org>]

Use 64bit lux64 to amplify lux values while preserving granularity.
Normalize illuminance_calibbias amplification value at 1024 instead of 1000
so we can avoid 64bit division (div_u64).

Signed-off-by: Bryan Freed <bfreed@chromium.org>
---
 drivers/staging/iio/light/tsl2583.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/iio/light/tsl2583.c b/drivers/staging/iio/light/tsl2583.c
index 5694610..0324ac1 100644
--- a/drivers/staging/iio/light/tsl2583.c
+++ b/drivers/staging/iio/light/tsl2583.c
@@ -146,7 +146,7 @@ static void taos_defaults(struct tsl2583_chip *chip)
 	chip->taos_settings.als_gain = 0;
 	/* this is actually an index into the gain table */
 	/* assume clear glass as default */
-	chip->taos_settings.als_gain_trim = 1000;
+	chip->taos_settings.als_gain_trim = 1024;
 	/* default gain trim to account for aperture effects */
 	chip->taos_settings.als_cal_target = 130;
 	/* Known external ALS reading used for calibration */
@@ -195,6 +195,7 @@ static int taos_get_lux(struct i2c_client *client)
 {
 	u16 ch0, ch1; /* separated ch0/ch1 data from device */
 	u32 lux; /* raw lux calculated from device data */
+	u64 lux64;
 	u32 ratio;
 	u8 buf[5];
 	struct taos_lux *p;
@@ -298,8 +299,10 @@ static int taos_get_lux(struct i2c_client *client)
 			chip->als_time_scale;
 
 	/* adjust for active gain scale */
-	lux >>= 13; /* tables have factor of 8192 builtin for accuracy */
-	lux = (lux * chip->taos_settings.als_gain_trim + 500) / 1000;
+	lux64 = lux;
+	lux64 = (lux64 * chip->taos_settings.als_gain_trim + 512) >> 10;
+	lux64 >>= 13; /* tables have factor of 8192 builtin for accuracy */
+	lux = lux64;
 	if (lux > TSL258X_LUX_CALC_OVER_FLOW) { /* check for overflow */
 return_max:
 		lux = TSL258X_LUX_CALC_OVER_FLOW;
-- 
1.7.3.1