iio: hid-sensors: Convert units and exponent

HID sensor hub specify a default unit and alternative units. This
along with unit exponent can be used adjust scale. This change
change HID sensor data units to IIO defined units for each
sensor type. So in this way user space can use a simply use:
"(data + offset) * scale" to get final result.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/common/hid-sensors/hid-sensor-attributes.c

@@ -26,6 +26,40 @@
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 
+struct {
+	u32 usage_id;
+	int unit; /* 0 for default others from HID sensor spec */
+	int scale_val0; /* scale, whole number */
+	int scale_val1; /* scale, fraction in micros */
+} static unit_conversion[] = {
+	{HID_USAGE_SENSOR_ACCEL_3D, 0, 9, 806650},
+	{HID_USAGE_SENSOR_ACCEL_3D,
+		HID_USAGE_SENSOR_UNITS_METERS_PER_SEC_SQRD, 1, 0},
+	{HID_USAGE_SENSOR_ACCEL_3D,
+		HID_USAGE_SENSOR_UNITS_G, 9, 806650},
+
+	{HID_USAGE_SENSOR_GYRO_3D, 0, 0, 17453},
+	{HID_USAGE_SENSOR_GYRO_3D,
+		HID_USAGE_SENSOR_UNITS_RADIANS_PER_SECOND, 1, 0},
+	{HID_USAGE_SENSOR_GYRO_3D,
+		HID_USAGE_SENSOR_UNITS_DEGREES_PER_SECOND, 0, 17453},
+
+	{HID_USAGE_SENSOR_COMPASS_3D, 0, 0, 1000},
+	{HID_USAGE_SENSOR_COMPASS_3D, HID_USAGE_SENSOR_UNITS_GAUSS, 1, 0},
+
+	{HID_USAGE_SENSOR_INCLINOMETER_3D, 0, 0, 17453},
+	{HID_USAGE_SENSOR_INCLINOMETER_3D,
+		HID_USAGE_SENSOR_UNITS_DEGREES, 0, 17453},
+	{HID_USAGE_SENSOR_INCLINOMETER_3D,
+		HID_USAGE_SENSOR_UNITS_RADIANS, 1, 0},
+
+	{HID_USAGE_SENSOR_ALS, 0, 1, 0},
+	{HID_USAGE_SENSOR_ALS, HID_USAGE_SENSOR_UNITS_LUX, 1, 0},
+
+	{HID_USAGE_SENSOR_PRESSURE, 0, 100000, 0},
+	{HID_USAGE_SENSOR_PRESSURE, HID_USAGE_SENSOR_UNITS_PASCAL, 1, 0},
+};
+
 static int pow_10(unsigned power)
 {
 	int i;
@@ -209,6 +243,86 @@ int hid_sensor_write_raw_hyst_value(struct hid_sensor_common *st,
 }
 EXPORT_SYMBOL(hid_sensor_write_raw_hyst_value);
 
+/*
+ * This fuction applies the unit exponent to the scale.
+ * For example:
+ * 9.806650 ->exp:2-> val0[980]val1[665000]
+ * 9.000806 ->exp:2-> val0[900]val1[80600]
+ * 0.174535 ->exp:2-> val0[17]val1[453500]
+ * 1.001745 ->exp:0-> val0[1]val1[1745]
+ * 1.001745 ->exp:2-> val0[100]val1[174500]
+ * 1.001745 ->exp:4-> val0[10017]val1[450000]
+ * 9.806650 ->exp:-2-> val0[0]val1[98066]
+ */
+static void adjust_exponent_micro(int *val0, int *val1, int scale0,
+				  int scale1, int exp)
+{
+	int i;
+	int x;
+	int res;
+	int rem;
+
+	if (exp > 0) {
+		*val0 = scale0 * pow_10(exp);
+		res = 0;
+		if (exp > 6) {
+			*val1 = 0;
+			return;
+		}
+		for (i = 0; i < exp; ++i) {
+			x = scale1 / pow_10(5 - i);
+			res += (pow_10(exp - 1 - i) * x);
+			scale1 = scale1 % pow_10(5 - i);
+		}
+		*val0 += res;
+			*val1 = scale1 * pow_10(exp);
+	} else if (exp < 0) {
+		exp = abs(exp);
+		if (exp > 6) {
+			*val0 = *val1 = 0;
+			return;
+		}
+		*val0 = scale0 / pow_10(exp);
+		rem = scale0 % pow_10(exp);
+		res = 0;
+		for (i = 0; i < (6 - exp); ++i) {
+			x = scale1 / pow_10(5 - i);
+			res += (pow_10(5 - exp - i) * x);
+			scale1 = scale1 % pow_10(5 - i);
+		}
+		*val1 = rem * pow_10(6 - exp) + res;
+	} else {
+		*val0 = scale0;
+		*val1 = scale1;
+	}
+}
+
+int hid_sensor_format_scale(u32 usage_id,
+			struct hid_sensor_hub_attribute_info *attr_info,
+			int *val0, int *val1)
+{
+	int i;
+	int exp;
+
+	*val0 = 1;
+	*val1 = 0;
+
+	for (i = 0; ARRAY_SIZE(unit_conversion); ++i) {
+		if (unit_conversion[i].usage_id == usage_id &&
+			unit_conversion[i].unit == attr_info->units) {
+			exp  = hid_sensor_convert_exponent(
+						attr_info->unit_expo);
+			adjust_exponent_micro(val0, val1,
+					unit_conversion[i].scale_val0,
+					unit_conversion[i].scale_val1, exp);
+			break;
+		}
+	}
+
+	return IIO_VAL_INT_PLUS_MICRO;
+}
+EXPORT_SYMBOL(hid_sensor_format_scale);
+
 int hid_sensor_parse_common_attributes(struct hid_sensor_hub_device *hsdev,
 					u32 usage_id,
 					struct hid_sensor_common *st)

include/linux/hid-sensor-hub.h

@@ -223,4 +223,8 @@ int hid_sensor_read_samp_freq_value(struct hid_sensor_common *st,
 int hid_sensor_get_usage_index(struct hid_sensor_hub_device *hsdev,
 				u32 report_id, int field_index, u32 usage_id);
 
+int hid_sensor_format_scale(u32 usage_id,
+			    struct hid_sensor_hub_attribute_info *attr_info,
+			    int *val0, int *val1);
+
 #endif