Re: [PATCH] iio: pressure: bmp280: fix bmp580 temp read

[Jonathan Cameron <jic23@kernel.org>]

On Sun,  2 Jun 2024 15:12:01 -0500
Adam Rizkalla <ajarizzo@gmail.com> wrote:

> Fix overflow when storing bmp580 temperature reading and preserve sign.
> 
> This patch re-applies the fix in [1] after the merge conflict resolution
> mentioned in [2].
> 
> [1] https://lore.kernel.org/all/Zin2udkXRD0+GrML@adam-asahi.lan/
> [2] https://lore.kernel.org/linux-kernel/20240531140621.264f0848@canb.auug.org.au/
> 
> Signed-off-by: Adam Rizkalla <ajarizzo@gmail.com>

Thanks! I was just about to email about this fix currently being lost in
linux-next.

Rather than dance around this, I'm going to pull the later part of Vasielios'
series off the togreg tree for now then reapply later once I have the fix
in my upstream.

It's a shame that we need to do the maths in driver to keep within range.
Maybe we can be cheeky and avoid doing the division?
I believe the IIO core formatting code should be fine with that as it
already casts up to 64 bits to do the maths.

(s64)*raw_temp * 250);

bmp580_temp_coeffs = {1, 18}

Anyhow, I've dropped (for now) the following patches from my togreg tree
  iio: pressure: bmp280: Generalize read_{temp,press,humid}() functions
  iio: pressure: bmp280: Add SCALE, RAW values in channels and refactorize them
  iio: pressure: bmp280: Add triggered buffer support

Jonathan

> ---
>  drivers/iio/pressure/bmp280-core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/pressure/bmp280-core.c b/drivers/iio/pressure/bmp280-core.c
> index 95c88b0e1c49..3a003843c79c 100644
> --- a/drivers/iio/pressure/bmp280-core.c
> +++ b/drivers/iio/pressure/bmp280-core.c
> @@ -1752,6 +1752,8 @@ static int bmp580_read_temp(struct bmp280_data *data, s32 *raw_temp)
>  		dev_err(data->dev, "reading temperature skipped\n");
>  		return -EIO;
>  	}
> +	*raw_temp = sign_extend32(*raw_temp, 23);
> +	*raw_temp = ((s64)*raw_temp * 1000) / (1 << 16);
>  
>  	return 0;
>  }
> @@ -2154,7 +2156,7 @@ static irqreturn_t bmp580_buffer_handler(int irq, void *p)
>  
>  static const int bmp580_oversampling_avail[] = { 1, 2, 4, 8, 16, 32, 64, 128 };
>  static const u8 bmp580_chip_ids[] = { BMP580_CHIP_ID, BMP580_CHIP_ID_ALT };
> -static const int bmp580_temp_coeffs[] = { 1000, 16 };
> +static const int bmp580_temp_coeffs[] = { 1, 0 };
>  static const int bmp580_press_coeffs[] = { 1, 64000};
>  
>  const struct bmp280_chip_info bmp580_chip_info = {
> @@ -2184,7 +2186,7 @@ const struct bmp280_chip_info bmp580_chip_info = {
>  	.iir_filter_coeff_default = 2,
>  
>  	.temp_coeffs = bmp580_temp_coeffs,
> -	.temp_coeffs_type = IIO_VAL_FRACTIONAL_LOG2,
> +	.temp_coeffs_type = IIO_VAL_INT,
>  	.press_coeffs = bmp580_press_coeffs,
>  	.press_coeffs_type = IIO_VAL_FRACTIONAL,
>