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


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