iio: cros_ec: Add sign vector in core for backward compatibility

To allow cros_ec iio core library to be used with legacy device, add a
vector to rotate sensor data if necessary: legacy devices are not
reporting data in HTML5/Android sensor referential.

Check the data is not rotated on recent chromebooks that use the HTML5
standard to present sensor data.
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c

@@ -101,6 +101,9 @@ int cros_ec_sensors_core_init(struct platform_device *pdev,
 		}
 		state->type = state->resp->info.type;
 		state->loc = state->resp->info.location;
+
+		/* Set sign vector, only used for backward compatibility. */
+		memset(state->sign, 1, CROS_EC_SENSOR_MAX_AXIS);
 	}
 
 	return 0;
@@ -303,6 +306,7 @@ static int cros_ec_sensors_read_data_unsafe(struct iio_dev *indio_dev,
 		if (ret < 0)
 			return ret;
 
+		*data *= st->sign[i];
 		data++;
 	}
 

include/linux/iio/common/cros_ec_sensors_core.h

@@ -66,7 +66,7 @@ struct cros_ec_sensors_core_state {
 		s16 offset;
 		u16 scale;
 	} calib[CROS_EC_SENSOR_MAX_AXIS];
-
+	s8 sign[CROS_EC_SENSOR_MAX_AXIS];
 	u8 samples[CROS_EC_SAMPLE_SIZE];
 
 	int (*read_ec_sensors_data)(struct iio_dev *indio_dev,