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Commit 014fcb1d authored by Bryan Freed's avatar Bryan Freed Committed by Greg Kroah-Hartman
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iio: light sensor: Improve granularity of tsl2583 lux values. 



When illuminance0_calibbias gets 4000 (for a 4x multiplier), we see lux
granularity of 4.  Reversing the order of the right shift and multiplication
retains the precision of the unadjusted lux value.

Signed-off-by: default avatarBryan Freed <bfreed@chromium.org>
Acked-by: default avatarJonathan Cameron <jic23@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent d666c0d4

drivers/staging/iio/light/tsl2583.c

+14 −3
Original line number Diff line number Diff line
@@ -194,6 +194,7 @@ static int taos_get_lux(struct iio_dev *indio_dev) 
{

	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;
@@ -297,9 +298,19 @@ static int taos_get_lux(struct iio_dev *indio_dev) 
		lux = (lux + (chip->als_time_scale >> 1)) /

			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;

	/* Adjust for active gain scale.

	 * The taos_device_lux tables above have a factor of 8192 built in,

	 * so we need to shift right.

	 * User-specified gain provides a multiplier.

	 * Apply user-specified gain before shifting right to retain precision.

	 * Use 64 bits to avoid overflow on multiplication.

	 * Then go back to 32 bits before division to avoid using div_u64().

	 */

	lux64 = lux;

	lux64 = lux64 * chip->taos_settings.als_gain_trim;

	lux64 >>= 13;

	lux = lux64;

	lux = (lux + 500) / 1000;

	if (lux > TSL258X_LUX_CALC_OVER_FLOW) { /* check for overflow */

return_max:

		lux = TSL258X_LUX_CALC_OVER_FLOW;