[PATCH V2] staging:iio:ad7606: fix voltage scales

[PATCH V2] staging:iio:ad7606: fix voltage scales

[Alexandru Ardelean]

Fixes commit 17be2a2905a6ec9aa27cd59521495e2f490d2af0 ("staging: iio:
ad7606: replace range/range_available with corresponding scale").

The AD7606 devices don't have a 2.5V voltage range, they have 5V & 10V
voltage range, which is selectable via the `gpio_range` descriptor.

The scales also seem to have been miscomputed, because when they were
applied to the raw values, the results differ from the expected values.
After checking the ADC transfer function in the datasheet, these were
re-computed.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---

Changelog V1 -> V2:
* changed 2.5/2**16 and 5/2**16 -> 5000/32768 and 10000/32768, because
  my computation of 32768 in power of 2 is also wrong; it's 2**15, not 2**16
  and the datasheet mentions 32768, so use that value

 drivers/staging/iio/adc/ad7606.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/iio/adc/ad7606.c b/drivers/staging/iio/adc/ad7606.c
index c5fe3003075b..87d5fb073c95 100644
--- a/drivers/staging/iio/adc/ad7606.c
+++ b/drivers/staging/iio/adc/ad7606.c
@@ -26,9 +26,11 @@
 
 #include "ad7606.h"
 
-/* Scales are computed as 2.5/2**16 and 5/2**16 respectively */
+/* Scales are computed as 5000/32768 and 10000/32768 respectively,
+ * so that when applied to the raw values they provide mV values
+ */
 static const unsigned int scale_avail[2][2] = {
-	{0, 38147}, {0, 76294}
+	{0, 152588}, {0, 305176}
 };
 
 static int ad7606_reset(struct ad7606_state *st)
-- 
2.17.1

Re: [PATCH V2] staging:iio:ad7606: fix voltage scales

[Jonathan Cameron]

On Thu, 13 Sep 2018 11:44:09 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> wrote:

> Fixes commit 17be2a2905a6ec9aa27cd59521495e2f490d2af0 ("staging: iio:
> ad7606: replace range/range_available with corresponding scale").
> 
> The AD7606 devices don't have a 2.5V voltage range, they have 5V & 10V
> voltage range, which is selectable via the `gpio_range` descriptor.
> 
> The scales also seem to have been miscomputed, because when they were
> applied to the raw values, the results differ from the expected values.
> After checking the ADC transfer function in the datasheet, these were
> re-computed.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
On thing inline.

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
> 
> Changelog V1 -> V2:
> * changed 2.5/2**16 and 5/2**16 -> 5000/32768 and 10000/32768, because
>   my computation of 32768 in power of 2 is also wrong; it's 2**15, not 2**16
>   and the datasheet mentions 32768, so use that value
> 
>  drivers/staging/iio/adc/ad7606.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/staging/iio/adc/ad7606.c b/drivers/staging/iio/adc/ad7606.c
> index c5fe3003075b..87d5fb073c95 100644
> --- a/drivers/staging/iio/adc/ad7606.c
> +++ b/drivers/staging/iio/adc/ad7606.c
> @@ -26,9 +26,11 @@
>  
>  #include "ad7606.h"
>  
> -/* Scales are computed as 2.5/2**16 and 5/2**16 respectively */

This isn't a kernel comment style. I'll fix up.

> +/* Scales are computed as 5000/32768 and 10000/32768 respectively,
> + * so that when applied to the raw values they provide mV values
> + */
>  static const unsigned int scale_avail[2][2] = {
> -	{0, 38147}, {0, 76294}
> +	{0, 152588}, {0, 305176}
>  };
>  
>  static int ad7606_reset(struct ad7606_state *st)