Re: [PATCH 2/3] iio: pressure: Support ROHM BU1390

[Matti Vaittinen]

On 9/8/23 21:45, Jonathan Cameron wrote:
> > +static int bm1390_read_temp(struct bm1390_data *data, int *temp)
> > +{
> > +	u8 temp_reg[2] __aligned(2);
> > +	__be16 *temp_raw;
> > +	int ret;
> > +	s16 val;
> > +	bool negative;
> > +
> > +	ret = regmap_bulk_read(data->regmap, BM1390_REG_TEMP_HI, &temp_reg,
> > +			       sizeof(temp_reg));
> > +	if (ret)
> > +		return ret;
> > +
> > +	if (temp_reg[0] & 0x80)
> > +		negative = true;
> > +	else
> > +		negative = false;
> > +
> > +	temp_raw = (__be16 *)&temp_reg[0];
> > +	val = be16_to_cpu(*temp_raw);
> > +
> > +	if (negative) {
> > +		/*
> > +		 * Two's complement. I am not sure if all supported
> > +		 * architectures actually use 2's complement represantation of
>
> AFAIK they do. Many IIO drivers would be broken if not..

Great. Then I think it means we really can treat the combined value of 
the registers as s16 BE. Should make this much simpler :)

> > +		 * signed ints. If yes, then we could just do the endianes
> > +		 * conversion and say this is the s16 value. However, as I
> > +		 * don't know, and as the conversion is pretty simple. let's
> > +		 * just convert the signed 2's complement to absolute value and
> > +		 * multiply by -1.
> > +		 */
> > +		val = ~val + 1;
> > +		val *= -1;
> > +	}
> > +
> > +	*temp = val;
> > +
> > +	return 0;
> > +}

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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