[PATCH] staging: iio: ad5933: fix handling of settling time cycles

[PATCH] staging: iio: ad5933: fix handling of settling time cycles

[Luis de Bethencourt]

Correctly handle the settling time cycles value. The else branch was an
impossible condition (> 1022 in the else branch of > 511) and the handling
of the values was dividing by 2 and 4, with a left shift, instead of
multiplying.

Based on the Table 13 at the bottom of Page 25 of the Data Sheet:
http://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf

Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
---

Hi,

I decided to use the hexadecimal values instead of (1 << 10) and (1 << 9), for
briefness, I could resend using those instead if it is prefered.

I also decided to use multiplications instead of right-shifts for readability.
I could use change that as well.

Thanks,
Luis

 drivers/staging/iio/impedance-analyzer/ad5933.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
index 9f43976..3a2cf8f3 100644
--- a/drivers/staging/iio/impedance-analyzer/ad5933.c
+++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
@@ -444,10 +444,13 @@ static ssize_t ad5933_store(struct device *dev,
 		st->settling_cycles = val;
 
 		/* 2x, 4x handling, see datasheet */
-		if (val > 511)
-			val = (val >> 1) | (1 << 9);
-		else if (val > 1022)
-			val = (val >> 2) | (3 << 9);
+		if (val & 0x400 && val & 0x200) {
+			val &= 0x1ff;
+			val *= 4;
+		} else if (val & 0x200) {
+			val &= 0x1ff;
+			val *= 2;
+		}
 
 		dat = cpu_to_be16(val);
 		ret = ad5933_i2c_write(st->client,
-- 
2.5.1

Re: [PATCH] staging: iio: ad5933: fix handling of settling time cycles

[Lars-Peter Clausen]

On 06/01/2016 05:55 PM, Luis de Bethencourt wrote:
> Correctly handle the settling time cycles value. The else branch was an
> impossible condition (> 1022 in the else branch of > 511) and the handling
> of the values was dividing by 2 and 4, with a left shift, instead of
> multiplying.
> 
> Based on the Table 13 at the bottom of Page 25 of the Data Sheet:
> http://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf
> 
> Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
> ---
> 
> Hi,
> 
> I decided to use the hexadecimal values instead of (1 << 10) and (1 << 9), for
> briefness, I could resend using those instead if it is prefered.
> 
> I also decided to use multiplications instead of right-shifts for readability.
> I could use change that as well.
> 
> Thanks,
> Luis
> 
>  drivers/staging/iio/impedance-analyzer/ad5933.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
> index 9f43976..3a2cf8f3 100644
> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
> @@ -444,10 +444,13 @@ static ssize_t ad5933_store(struct device *dev,
>  		st->settling_cycles = val;
>  
>  		/* 2x, 4x handling, see datasheet */
> -		if (val > 511)
> -			val = (val >> 1) | (1 << 9);
> -		else if (val > 1022)
> -			val = (val >> 2) | (3 << 9);
> +		if (val & 0x400 && val & 0x200) {
> +			val &= 0x1ff;
> +			val *= 4;
> +		} else if (val & 0x200) {
> +			val &= 0x1ff;
> +			val *= 2;
> +		}

This does not look correct. D10 and D9 select an additional multiplier of
either 1, 2 or 4. So dividing the value before writing it to the register is
the right approach in that case. Just flipping the order in which the
conditions are evaluated should be sufficient.

>  
>  		dat = cpu_to_be16(val);
>  		ret = ad5933_i2c_write(st->client,
> 

Re: [PATCH] staging: iio: ad5933: fix handling of settling time cycles

[Luis de Bethencourt]

On 01/06/16 17:22, Lars-Peter Clausen wrote:
> On 06/01/2016 05:55 PM, Luis de Bethencourt wrote:
>> Correctly handle the settling time cycles value. The else branch was an
>> impossible condition (> 1022 in the else branch of > 511) and the handling
>> of the values was dividing by 2 and 4, with a left shift, instead of
>> multiplying.
>>
>> Based on the Table 13 at the bottom of Page 25 of the Data Sheet:
>> http://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf
>>
>> Signed-off-by: Luis de Bethencourt <luisbg@osg.samsung.com>
>> ---
>>
>> Hi,
>>
>> I decided to use the hexadecimal values instead of (1 << 10) and (1 << 9), for
>> briefness, I could resend using those instead if it is prefered.
>>
>> I also decided to use multiplications instead of right-shifts for readability.
>> I could use change that as well.
>>
>> Thanks,
>> Luis
>>
>>  drivers/staging/iio/impedance-analyzer/ad5933.c | 11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/staging/iio/impedance-analyzer/ad5933.c b/drivers/staging/iio/impedance-analyzer/ad5933.c
>> index 9f43976..3a2cf8f3 100644
>> --- a/drivers/staging/iio/impedance-analyzer/ad5933.c
>> +++ b/drivers/staging/iio/impedance-analyzer/ad5933.c
>> @@ -444,10 +444,13 @@ static ssize_t ad5933_store(struct device *dev,
>>  		st->settling_cycles = val;
>>  
>>  		/* 2x, 4x handling, see datasheet */
>> -		if (val > 511)
>> -			val = (val >> 1) | (1 << 9);
>> -		else if (val > 1022)
>> -			val = (val >> 2) | (3 << 9);
>> +		if (val & 0x400 && val & 0x200) {
>> +			val &= 0x1ff;
>> +			val *= 4;
>> +		} else if (val & 0x200) {
>> +			val &= 0x1ff;
>> +			val *= 2;
>> +		}
> 
> This does not look correct. D10 and D9 select an additional multiplier of
> either 1, 2 or 4. So dividing the value before writing it to the register is
> the right approach in that case. Just flipping the order in which the
> conditions are evaluated should be sufficient.
> 
>>  
>>  		dat = cpu_to_be16(val);
>>  		ret = ad5933_i2c_write(st->client,
>>
> 

I misunderstood the register being read instead of being written. Looking at it
now, I have no idea why. Sorry.

Will resend a patch flipping the order of conditions.

Thanks for the review,
Luis