iio: imu: lsm6dsx: Add ACPI mount matrix retrieval

DSDT ROTM method seen in the wild with SMO8B30 _HID.
Making assumption it is similar to that used for bmc150 plus
information from Darrell that the rotation is out by 90 degrees at boot.

Method (ROTM, 0, NotSerialized)
{
    Name (RBUF, Package (0x03)
    {
        "0 -1 0",
        "1 0 0",
        "0 0 1"
    })
    Return (RBUF) /* \_SB_.PCI0.I2C5.DEV_.ROTM.RBUF */
}
Reported-by: Darrell Kavanagh <darrell.kavanagh@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Tested-by: Darrell Kavanagh <darrell.kavanagh@gmail.org>
Link: https://lore.kernel.org/r/20230130201018.981024-3-jic23@kernel.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c

@@ -56,6 +56,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/acpi.h>
 #include <linux/delay.h>
 #include <linux/iio/events.h>
 #include <linux/iio/iio.h>
@@ -2624,6 +2625,73 @@ static int st_lsm6dsx_init_regulators(struct device *dev)
 	return 0;
 }
 
+#ifdef CONFIG_ACPI
+
+static int lsm6dsx_get_acpi_mount_matrix(struct device *dev,
+					 struct iio_mount_matrix *orientation)
+{
+	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	union acpi_object *obj, *elements;
+	acpi_status status;
+	int i, j, val[3];
+	char *str;
+
+	if (!has_acpi_companion(dev))
+		return -EINVAL;
+
+	if (!acpi_has_method(adev->handle, "ROTM"))
+		return -EINVAL;
+
+	status = acpi_evaluate_object(adev->handle, "ROTM", NULL, &buffer);
+	if (ACPI_FAILURE(status)) {
+		dev_warn(dev, "Failed to get ACPI mount matrix: %d\n", status);
+		return -EINVAL;
+	}
+
+	obj = buffer.pointer;
+	if (obj->type != ACPI_TYPE_PACKAGE || obj->package.count != 3)
+		goto unknown_format;
+
+	elements = obj->package.elements;
+	for (i = 0; i < 3; i++) {
+		if (elements[i].type != ACPI_TYPE_STRING)
+			goto unknown_format;
+
+		str = elements[i].string.pointer;
+		if (sscanf(str, "%d %d %d", &val[0], &val[1], &val[2]) != 3)
+			goto unknown_format;
+
+		for (j = 0; j < 3; j++) {
+			switch (val[j]) {
+			case -1: str = "-1"; break;
+			case 0:  str = "0";  break;
+			case 1:  str = "1";  break;
+			default: goto unknown_format;
+			}
+			orientation->rotation[i * 3 + j] = str;
+		}
+	}
+
+	kfree(buffer.pointer);
+	return 0;
+
+unknown_format:
+	dev_warn(dev, "Unknown ACPI mount matrix format, ignoring\n");
+	kfree(buffer.pointer);
+	return -EINVAL;
+}
+
+#else
+
+static int lsm6dsx_get_acpi_mount_matrix(struct device *dev,
+					  struct iio_mount_matrix *orientation)
+{
+	return false;
+}
+
+#endif
+
 int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id,
 		     struct regmap *regmap)
 {
@@ -2698,9 +2766,12 @@ int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id,
 			return err;
 	}
 
-	err = iio_read_mount_matrix(hw->dev, &hw->orientation);
-	if (err)
-		return err;
+	err = lsm6dsx_get_acpi_mount_matrix(hw->dev, &hw->orientation);
+	if (err) {
+		err = iio_read_mount_matrix(hw->dev, &hw->orientation);
+		if (err)
+			return err;
+	}
 
 	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
 		if (!hw->iio_devs[i])