Re: [bmp280 v1 1/6] iio: pressure: bmp280: correct meas_time_us calculation

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Sun,  3 Aug 2025 16:07:57 +0200
Achim Gratz <Achim.Gratz@Stromeko.DE> wrote:

> Based on an observation and partial patch by David Lechner.
> 
> There was also a thinko in bmp280_wait_conv: data->oversampling_humid
> can actually be 0 (for an oversampling_ratio of 1), so it can not be
> used to detect the presence of the humidity measurement capability.
> Use data->chip_info->oversampling_humid_avail instead, which is NULL
> for chips that cannot measure humidity and therefore need to skip that
> part of the calculation.
> 
> Note: Since the BMx280 device support was added, oversampling=0
> actually is a valid setting (that channels measurement is off), but
> allowing that setting by changing the data structure to hold the
> actual value instead of its ilog2 would require more extensive changes
> elsewhere in the code.
> 
> Suggested-by: David Lechner <dlechner@baylibre.com>
> Signed-off-by: Achim Gratz <Achim.Gratz@Stromeko.DE>
Needs a fixes tag if it is correcting something.

> ---
>  drivers/iio/pressure/bmp280-core.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 74505c9ec1a0..3213dcadba28 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -1042,14 +1042,13 @@ static int bmp280_wait_conv(struct bmp280_data *data)
>  	unsigned int reg, meas_time_us;
>  	int ret;
>  
> +	meas_time_us = BMP280_MEAS_OFFSET;
> +

I'm not following this. Why are we now effectively adding MP280_MEAS_OFFSET
that we weren't before whether or not oversampling is enabled?

>  	/* Check if we are using a BME280 device */
> -	if (data->oversampling_humid)
> -		meas_time_us = BMP280_PRESS_HUMID_MEAS_OFFSET +
> +	if (data->chip_info->oversampling_humid_avail)
> +		meas_time_us += BMP280_PRESS_HUMID_MEAS_OFFSET +
>  				BIT(data->oversampling_humid) * BMP280_MEAS_DUR;
>  
> -	else
> -		meas_time_us = 0;
> -
>  	/* Pressure measurement time */
>  	meas_time_us += BMP280_PRESS_HUMID_MEAS_OFFSET +
>  			BIT(data->oversampling_press) * BMP280_MEAS_DUR;