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

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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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