[PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Nicola Corna]

The maximum possible value for the relative humidity is 55575 (100%RH).
This value, if shifted right by 2 bits, uses 14 bits and masking it with
a 12 bit mask removes 2 meaningful bits.
The masking has been replaced with a range check that sets the minimum
value at 786 (0%RH) and the maximum at 13894 (100%RH).

Signed-off-by: Nicola Corna <nicola@corna.info>
---
 drivers/iio/humidity/si7020.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
index fa3b809..d27e2f2 100644
--- a/drivers/iio/humidity/si7020.c
+++ b/drivers/iio/humidity/si7020.c
@@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
 		if (ret < 0)
 			return ret;
 		*val = ret >> 2;
+		/*
+		 * Humidity values can sligthly exceed the 0-100%RH
+		 * range and should be corrected by software
+		 */
 		if (chan->type == IIO_HUMIDITYRELATIVE)
-			*val &= GENMASK(11, 0);
+			clamp_val(*val, 786, 13894);
 		return IIO_VAL_INT;
 	case IIO_CHAN_INFO_SCALE:
 		if (chan->type == IIO_TEMP)
-- 
2.5.0

Re: [PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Hartmut Knaack]

Nicola Corna schrieb am 22.08.2015 um 20:01:
> The maximum possible value for the relative humidity is 55575 (100%RH).
> This value, if shifted right by 2 bits, uses 14 bits and masking it with
> a 12 bit mask removes 2 meaningful bits.
> The masking has been replaced with a range check that sets the minimum
> value at 786 (0%RH) and the maximum at 13894 (100%RH).
> 
> Signed-off-by: Nicola Corna <nicola@corna.info>

Might be discussable, if we want the upper boundary to be rounded down,
so we just barely reach 100% rather than slightly exceeding it (in numbers,
that is 99,998 vs 100,006). Using 13893 might be the better value. Other
than that (and a typo in the comment) looking good, so:
Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
> ---
>  drivers/iio/humidity/si7020.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
> index fa3b809..d27e2f2 100644
> --- a/drivers/iio/humidity/si7020.c
> +++ b/drivers/iio/humidity/si7020.c
> @@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>  		if (ret < 0)
>  			return ret;
>  		*val = ret >> 2;
> +		/*
> +		 * Humidity values can sligthly exceed the 0-100%RH

Typo: slightly

> +		 * range and should be corrected by software
> +		 */
>  		if (chan->type == IIO_HUMIDITYRELATIVE)
> -			*val &= GENMASK(11, 0);
> +			clamp_val(*val, 786, 13894);
>  		return IIO_VAL_INT;
>  	case IIO_CHAN_INFO_SCALE:
>  		if (chan->type == IIO_TEMP)
> 

Re: [PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Hartmut Knaack]

Hartmut Knaack schrieb am 22.08.2015 um 23:44:
> Nicola Corna schrieb am 22.08.2015 um 20:01:
>> The maximum possible value for the relative humidity is 55575 (100%RH).
>> This value, if shifted right by 2 bits, uses 14 bits and masking it with
>> a 12 bit mask removes 2 meaningful bits.
>> The masking has been replaced with a range check that sets the minimum
>> value at 786 (0%RH) and the maximum at 13894 (100%RH).
>>
>> Signed-off-by: Nicola Corna <nicola@corna.info>
> 
> Might be discussable, if we want the upper boundary to be rounded down,
> so we just barely reach 100% rather than slightly exceeding it (in numbers,
> that is 99,998 vs 100,006). Using 13893 might be the better value. Other
> than that (and a typo in the comment) looking good, so:
> Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>

On second thought, this is not exactly how clamp_val works. It will return
a value between the boundaries, so usage is like this:
*val = clamp_val(*val, 786, 13894)

If my suggestions are addressed, you can keep my Reviewed-by tag.
Thanks,

Hartmut

>> ---
>>  drivers/iio/humidity/si7020.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>> index fa3b809..d27e2f2 100644
>> --- a/drivers/iio/humidity/si7020.c
>> +++ b/drivers/iio/humidity/si7020.c
>> @@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>>  		if (ret < 0)
>>  			return ret;
>>  		*val = ret >> 2;
>> +		/*
>> +		 * Humidity values can sligthly exceed the 0-100%RH
> 
> Typo: slightly
> 
>> +		 * range and should be corrected by software
>> +		 */
>>  		if (chan->type == IIO_HUMIDITYRELATIVE)
>> -			*val &= GENMASK(11, 0);
>> +			clamp_val(*val, 786, 13894);
>>  		return IIO_VAL_INT;
>>  	case IIO_CHAN_INFO_SCALE:
>>  		if (chan->type == IIO_TEMP)
>>
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

Re: [PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Nicola Corna]

August 22 2015 11:54 PM, "Hartmut Knaack" <knaack.h@gmx.de> wrote:
> Hartmut Knaack schrieb am 22.08.2015 um 23:44:
> 
>> Nicola Corna schrieb am 22.08.2015 um 20:01:
>>> The maximum possible value for the relative humidity is 55575 (100%RH).
>>> This value, if shifted right by 2 bits, uses 14 bits and masking it with
>>> a 12 bit mask removes 2 meaningful bits.
>>> The masking has been replaced with a range check that sets the minimum
>>> value at 786 (0%RH) and the maximum at 13894 (100%RH).
>>> 
>>> Signed-off-by: Nicola Corna <nicola@corna.info>
>> 
>> Might be discussable, if we want the upper boundary to be rounded down,
>> so we just barely reach 100% rather than slightly exceeding it (in numbers,
>> that is 99,998 vs 100,006). Using 13893 might be the better value. Other
>> than that (and a typo in the comment) looking good, so:
>> Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
> 
> On second thought, this is not exactly how clamp_val works. It will return
> a value between the boundaries, so usage is like this:
> *val = clamp_val(*val, 786, 13894)
> 

I've tested clamp_val(*val, 786, 13894) and the minimum returned value is 786
while the maximum is 13894; shouldn't the line be like this?
*val = clamp_val(*val, 786, 13893)
Now the minimum value is 786 (exactly 0%RH), while the maximum (as you pointed
out) is 13893 (99,998%RH).

Nicola Corna

> If my suggestions are addressed, you can keep my Reviewed-by tag.
> Thanks,
> 
> Hartmut
> 
>>> ---
>>> drivers/iio/humidity/si7020.c | 6 +++++-
>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>>> index fa3b809..d27e2f2 100644
>>> --- a/drivers/iio/humidity/si7020.c
>>> +++ b/drivers/iio/humidity/si7020.c
>>> @@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>>> if (ret < 0)
>>> return ret;
>>> *val = ret >> 2;
>>> + /*
>>> + * Humidity values can sligthly exceed the 0-100%RH
>> 
>> Typo: slightly
>> 
>>> + * range and should be corrected by software
>>> + */
>>> if (chan->type == IIO_HUMIDITYRELATIVE)
>>> - *val &= GENMASK(11, 0);
>>> + clamp_val(*val, 786, 13894);
>>> return IIO_VAL_INT;
>>> case IIO_CHAN_INFO_SCALE:
>>> if (chan->type == IIO_TEMP)
>> 
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>> the body of a message to majordomo@vger.kernel.org
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Re: [PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Hartmut Knaack]

Nicola Corna schrieb am 23.08.2015 um 09:41:
> August 22 2015 11:54 PM, "Hartmut Knaack" <knaack.h@gmx.de> wrote:
>> Hartmut Knaack schrieb am 22.08.2015 um 23:44:
>>
>>> Nicola Corna schrieb am 22.08.2015 um 20:01:
>>>> The maximum possible value for the relative humidity is 55575 (100%RH).
>>>> This value, if shifted right by 2 bits, uses 14 bits and masking it with
>>>> a 12 bit mask removes 2 meaningful bits.
>>>> The masking has been replaced with a range check that sets the minimum
>>>> value at 786 (0%RH) and the maximum at 13894 (100%RH).
>>>>
>>>> Signed-off-by: Nicola Corna <nicola@corna.info>
>>>
>>> Might be discussable, if we want the upper boundary to be rounded down,
>>> so we just barely reach 100% rather than slightly exceeding it (in numbers,
>>> that is 99,998 vs 100,006). Using 13893 might be the better value. Other
>>> than that (and a typo in the comment) looking good, so:
>>> Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
>>
>> On second thought, this is not exactly how clamp_val works. It will return
>> a value between the boundaries, so usage is like this:
>> *val = clamp_val(*val, 786, 13894)
>>
> 
> I've tested clamp_val(*val, 786, 13894) and the minimum returned value is 786
> while the maximum is 13894; shouldn't the line be like this?
> *val = clamp_val(*val, 786, 13893)
> Now the minimum value is 786 (exactly 0%RH), while the maximum (as you pointed
> out) is 13893 (99,998%RH).
> 
> Nicola Corna
> 

Using 13893 as top boundary is my preference, although I would not
completely object against 13894. So either way would be fine with me.

>> If my suggestions are addressed, you can keep my Reviewed-by tag.
>> Thanks,
>>
>> Hartmut
>>
>>>> ---
>>>> drivers/iio/humidity/si7020.c | 6 +++++-
>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>>>> index fa3b809..d27e2f2 100644
>>>> --- a/drivers/iio/humidity/si7020.c
>>>> +++ b/drivers/iio/humidity/si7020.c
>>>> @@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>>>> if (ret < 0)
>>>> return ret;
>>>> *val = ret >> 2;
>>>> + /*
>>>> + * Humidity values can sligthly exceed the 0-100%RH
>>>
>>> Typo: slightly
>>>
>>>> + * range and should be corrected by software
>>>> + */
>>>> if (chan->type == IIO_HUMIDITYRELATIVE)
>>>> - *val &= GENMASK(11, 0);
>>>> + clamp_val(*val, 786, 13894);
>>>> return IIO_VAL_INT;
>>>> case IIO_CHAN_INFO_SCALE:
>>>> if (chan->type == IIO_TEMP)
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at http://vger.kernel.org/majordomo-info.html
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