Re: [PATCH] IIO: BME280: Humidity: Changes to the humidity ctrl_hum require a write to ctrl_meas.

[Colin Foe-Parker <colin.foeparker@aclima.io>]

Hi Andreas,

On Thu, Aug 24, 2017 at 10:52 PM, Andreas Klinger <ak@it-klinger.de> wrote:
> Hi Colin,
>
> Colin Parker <colin.foeparker@aclima.io> schrieb am Thu, 24. Aug 16:54:
>> From: Colin Parker <colin.parker@aclima.io>
>>
>> This results in inaccurate Humidity readings that tend to not fluxuate.
>>
>> Update the ordering of the register writes so that ctrl_meas is written
>> after ctrl_hum. This is taken from section 5.4.3 of the datasheet.
>>
>> "https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280_DS001-11.pdf"
>
> this part of the patch is already covered by commit afb2c3851b: "iio: bmp280:
> properly initialize device for humidity reading"

Thanks for pointing out the duplication of efforts!  I dug through the
fixes-togreg branch and found the changes you are referencing.

I think that there might still be an issue there.  I believe that the
regmap_update_bits function will only write to the ctrl_meas register
if there is a difference in the register value vs what is in the
regmap cache.  So in the situation where someone wanted to update the
humidity sampling configuration, I don't think the write to the
ctrl_meas write would go out on the bus.  And as a consequence, the
changes to the humidity settings wouldn't become effective.

What is your take?  I can refactor my patch to just fix that part if
you see the same bug.

-Colin

>
> Andreas
>
>>
>> Also writes to the config register can be ignored if the device is in Normal Mode.
>> Change the device to sleep mode before updating the config register.
>> This has the nice side effect of guaranteeing that the regmap_update_bits
>> function actually updates the driver and not just verifies the setting in its cache.
>>
>> Signed-off-by: Colin Parker <colin.parker@aclima.io>
>> ---
>>  drivers/iio/pressure/bmp280-core.c | 22 +++++++++++++++-------
>>  1 file changed, 15 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
>> index d82b788..85aa24c 100644
>> --- a/drivers/iio/pressure/bmp280-core.c
>> +++ b/drivers/iio/pressure/bmp280-core.c
>> @@ -559,10 +559,7 @@ static int bmp280_chip_config(struct bmp280_data *data)
>>                 BMP280_OSRS_PRESS_X(data->oversampling_press + 1);
>>
>>       ret = regmap_update_bits(data->regmap, BMP280_REG_CTRL_MEAS,
>> -                              BMP280_OSRS_TEMP_MASK |
>> -                              BMP280_OSRS_PRESS_MASK |
>> -                              BMP280_MODE_MASK,
>> -                              osrs | BMP280_MODE_NORMAL);
>> +                              BMP280_MODE_MASK, BMP280_MODE_SLEEP);
>>       if (ret < 0) {
>>               dev_err(data->dev,
>>                       "failed to write ctrl_meas register\n");
>> @@ -578,6 +575,17 @@ static int bmp280_chip_config(struct bmp280_data *data)
>>               return ret;
>>       }
>>
>> +     ret = regmap_update_bits(data->regmap, BMP280_REG_CTRL_MEAS,
>> +                              BMP280_OSRS_TEMP_MASK |
>> +                              BMP280_OSRS_PRESS_MASK |
>> +                              BMP280_MODE_MASK,
>> +                              osrs | BMP280_MODE_NORMAL);
>> +     if (ret < 0) {
>> +             dev_err(data->dev,
>> +                     "failed to write ctrl_meas register\n");
>> +             return ret;
>> +     }
>> +
>>       return ret;
>>  }
>>
>> @@ -597,14 +605,14 @@ static const struct bmp280_chip_info bmp280_chip_info = {
>>
>>  static int bme280_chip_config(struct bmp280_data *data)
>>  {
>> -     int ret = bmp280_chip_config(data);
>>       u8 osrs = BMP280_OSRS_HUMIDITIY_X(data->oversampling_humid + 1);
>> +     int ret = regmap_update_bits(data->regmap, BMP280_REG_CTRL_HUMIDITY,
>> +                               BMP280_OSRS_HUMIDITY_MASK, osrs);
>>
>>       if (ret < 0)
>>               return ret;
>>
>> -     return regmap_update_bits(data->regmap, BMP280_REG_CTRL_HUMIDITY,
>> -                               BMP280_OSRS_HUMIDITY_MASK, osrs);
>> +     return bmp280_chip_config(data);
>>  }
>>
>>  static const struct bmp280_chip_info bme280_chip_info = {
>> --
>> 2.1.4
>>
>> --
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>
> --



-- 
Colin Parker


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