* [PATCH v2] iio: light sensor: Improve granularity of tsl2583 lux values.
@ 2011-12-02 22:19 Bryan Freed
2011-12-04 17:23 ` Jonathan Cameron
0 siblings, 1 reply; 3+ messages in thread
From: Bryan Freed @ 2011-12-02 22:19 UTC (permalink / raw)
To: jbrenner; +Cc: linux-iio, jic23, gregkh, linux-kernel, Bryan Freed
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: Bryan Freed <bfreed@chromium.org>
---
drivers/staging/iio/light/tsl2583.c | 17 ++++++++++++++---
1 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/drivers/staging/iio/light/tsl2583.c b/drivers/staging/iio/light/tsl2583.c
index 80f77cf..25f4c1d 100644
--- a/drivers/staging/iio/light/tsl2583.c
+++ b/drivers/staging/iio/light/tsl2583.c
@@ -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;
--
1.7.3.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v2] iio: light sensor: Improve granularity of tsl2583 lux values.
2011-12-02 22:19 [PATCH v2] iio: light sensor: Improve granularity of tsl2583 lux values Bryan Freed
@ 2011-12-04 17:23 ` Jonathan Cameron
2011-12-09 16:29 ` Jon Brenner
0 siblings, 1 reply; 3+ messages in thread
From: Jonathan Cameron @ 2011-12-04 17:23 UTC (permalink / raw)
To: Bryan Freed; +Cc: jbrenner, linux-iio, jic23, gregkh, linux-kernel
On 12/02/2011 10:19 PM, Bryan Freed wrote:
> 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.
Looks sensible to me, but having said that, Greg, please leave a little
while for Jon Brenner to get to it as he clearly knows this driver
a lot better than me!
>
> Signed-off-by: Bryan Freed <bfreed@chromium.org>
Acked-by: Jonathan Cameron <jic23@kernel.org>
> ---
> drivers/staging/iio/light/tsl2583.c | 17 ++++++++++++++---
> 1 files changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/iio/light/tsl2583.c b/drivers/staging/iio/light/tsl2583.c
> index 80f77cf..25f4c1d 100644
> --- a/drivers/staging/iio/light/tsl2583.c
> +++ b/drivers/staging/iio/light/tsl2583.c
> @@ -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;
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] iio: light sensor: Improve granularity of tsl2583 lux values.
2011-12-04 17:23 ` Jonathan Cameron
@ 2011-12-09 16:29 ` Jon Brenner
0 siblings, 0 replies; 3+ messages in thread
From: Jon Brenner @ 2011-12-09 16:29 UTC (permalink / raw)
To: Jonathan Cameron; +Cc: Bryan Freed, linux-iio, jic23, gregkh, linux-kernel
Acked-by: Jon Brenner <jbrenner@taosinc.com>
On Sun, 2011-12-04 at 17:23 +0000, Jonathan Cameron wrote:
> On 12/02/2011 10:19 PM, Bryan Freed wrote:
> > When illuminance0_calibbias gets 4000 (for a 4x multiplier), we see lux
> > granularity of 4. Reversing the order of the right shift and multiplic=
ation
> > retains the precision of the unadjusted lux value.
> Looks sensible to me, but having said that, Greg, please leave a little
> while for Jon Brenner to get to it as he clearly knows this driver
> a lot better than me!
> >=20
> > Signed-off-by: Bryan Freed <bfreed@chromium.org>
> Acked-by: Jonathan Cameron <jic23@kernel.org>
> > ---
> > drivers/staging/iio/light/tsl2583.c | 17 ++++++++++++++---
> > 1 files changed, 14 insertions(+), 3 deletions(-)
> >=20
> > diff --git a/drivers/staging/iio/light/tsl2583.c b/drivers/staging/iio/=
light/tsl2583.c
> > index 80f77cf..25f4c1d 100644
> > --- a/drivers/staging/iio/light/tsl2583.c
> > +++ b/drivers/staging/iio/light/tsl2583.c
> > @@ -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 =3D (lux + (chip->als_time_scale >> 1)) /
> > chip->als_time_scale;
> > =20
> > - /* adjust for active gain scale */
> > - lux >>=3D 13; /* tables have factor of 8192 builtin for accuracy */
> > - lux =3D (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 precisio=
n.
> > + * Use 64 bits to avoid overflow on multiplication.
> > + * Then go back to 32 bits before division to avoid using div_u64().
> > + */
> > + lux64 =3D lux;
> > + lux64 =3D lux64 * chip->taos_settings.als_gain_trim;
> > + lux64 >>=3D 13;
> > + lux =3D lux64;
> > + lux =3D (lux + 500) / 1000;
> > if (lux > TSL258X_LUX_CALC_OVER_FLOW) { /* check for overflow */
> > return_max:
> > lux =3D TSL258X_LUX_CALC_OVER_FLOW;
>=20
^ permalink raw reply [flat|nested] 3+ messages in thread
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2011-12-04 17:23 ` Jonathan Cameron
2011-12-09 16:29 ` Jon Brenner
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