Re: Replying to: [PATCH] iio pressure: bmp280: Fix BMP580 temperature reading

[Adam Rizkalla <ajarizzo@gmail.com>]

On Thu, May 02, 2024 at 07:16:16PM +0200, Vasileios Amoiridis wrote:
> Hi Angel!
> 
> Indeed the datasheet says that the pressure is a signed value. But this comes
> in contrast with 2 things:
> 
> 1) The BMP58x sensor does not have a compensation function so the value from the
> sensor is a pressure value just in different unit from the one reported by IIO.
> And the sensor is able to report in between 30-125kPa according to the
> datasheet which are both positive values so it makes more sense to be an
> unsigned value.
> 
> 2) According to the BMP5 sensor API [1] provided by Bosch, the pressure is
> declared as an unsigned value.
> 
> So, what should we trust?
> 
> [1]: https://github.com/boschsensortec/BMP5_SensorAPI/blob/master/bmp5_defs.h#L895

The pressure sensor reading cannot be negative, as the pressure range of the sensor
is 300 - 1250 hPa,so this change does not need to be applied for bmp580_read_press().
Also, the overflow issue does not happen with the pressure reading since the value
read back from the device is scaled up only by 2^6 for pressure vs 2^16 for temperature,
so multiplying by 1000 even for the maximum value would still fit in a 32-bit signed
integer. Temperature ranges above ~32.767C, however, will overflow a 32-bit signed
integer when multiplied by 2^16 * 1000 which is why this change is necessary only for
temperature readings.

Hope this helps clarify.

Best,
Adam