[PATCH] iio: imu: inv_mpu6050: fix magnetometer scale of Y and Z axes

[Arnav Kapoor <kapoorarnav43@gmail.com>]

inv_mpu_magn_get_scale() returns st->magn_raw_to_gauss[chan->address],
where magn_raw_to_gauss[] holds one coefficient per axis, computed in
inv_magn_init() from the per-axis factory sensitivity adjustment values
(ASAX, ASAY, ASAZ) of the AK8975/AK8963 magnetometer.

However INV_MPU9X50_MAGN_CHAN() never sets .address, so it is 0 for all
three magnetometer channels. As a result the Y and Z channels report the
scale computed from the X axis adjustment value, and userspace scales
the Y and Z readings with the wrong per-axis calibration.

Set .address to the axis index (0 for X, 1 for Y, 2 for Z) in the
channel macro, matching the order used to fill magn_raw_to_gauss[].

Fixes: b1392de06184 ("iio: imu: inv_mpu6050: add MPU925x magnetometer support")
Assisted-by: LLM
Signed-off-by: Arnav Kapoor <kapoorarnav43@gmail.com>
---
Compile-tested only (W=1); I don't have MPU9150/MPU925x hardware. I
checked the built object: before this patch the X, Y and Z magnetometer
channels all have .address == 0, after it they have 0, 1 and 2.

 drivers/iio/imu/inv_mpu6050/inv_mpu_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
index 38c3f3b398d4..1614f49be66c 100644
--- a/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
+++ b/drivers/iio/imu/inv_mpu6050/inv_mpu_core.c
@@ -1576,6 +1576,8 @@ static const unsigned long inv_mpu_scan_masks[] = {
 		.type = IIO_MAGN,					\
 		.modified = 1,						\
 		.channel2 = _chan2,					\
+		/* index of the axis in magn_raw_to_gauss[] */		\
+		.address = (_chan2) - IIO_MOD_X,			\
 		.info_mask_separate = BIT(IIO_CHAN_INFO_SCALE) |	\
 				      BIT(IIO_CHAN_INFO_RAW),		\
 		.scan_index = _index,					\
-- 
2.53.0