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

~~ When things go utterly wrong vim users can always type :help! ~~

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