iio: ak8975 : Add AK8963 compatibility mode support

AK8963 and AK8975 use same register definitions, except the range
of X,Y,Z values. Added support of 8963 based on i2c_device_id.
Unfortunately there is no way to detect the type via registers,
both device registers return 0x48 as id of chipset.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/magnetometer/Kconfig

@@ -11,7 +11,8 @@ config AK8975
 	depends on GPIOLIB
 	help
 	  Say yes here to build support for Asahi Kasei AK8975 3-Axis
-	  Magnetometer.
+	  Magnetometer. This driver can also support AK8963, if i2c
+	  device name is identified as ak8963.
 
 	  To compile this driver as a module, choose M here: the module
 	  will be called ak8975.

drivers/iio/magnetometer/ak8975.c

@@ -85,7 +85,14 @@
 #define AK8975_MAX_CONVERSION_TIMEOUT	500
 #define AK8975_CONVERSION_DONE_POLL_TIME 10
 #define AK8975_DATA_READY_TIMEOUT	((100*HZ)/1000)
-#define RAW_TO_GAUSS(asa) ((((asa) + 128) * 3000) / 256)
+#define RAW_TO_GAUSS_8975(asa) ((((asa) + 128) * 3000) / 256)
+#define RAW_TO_GAUSS_8963(asa) ((((asa) + 128) * 6000) / 256)
+
+/* Compatible Asahi Kasei Compass parts */
+enum asahi_compass_chipset {
+	AK8975,
+	AK8963,
+};
 
 /*
  * Per-instance context data for the device.
@@ -101,6 +108,7 @@ struct ak8975_data {
 	int			eoc_irq;
 	wait_queue_head_t	data_ready_queue;
 	unsigned long		flags;
+	enum asahi_compass_chipset chipset;
 };
 
 static const int ak8975_index_to_reg[] = {
@@ -272,9 +280,21 @@ static int ak8975_setup(struct i2c_client *client)
  * Since ASA doesn't change, we cache the resultant scale factor into the
  * device context in ak8975_setup().
  */
-	data->raw_to_gauss[0] = RAW_TO_GAUSS(data->asa[0]);
-	data->raw_to_gauss[1] = RAW_TO_GAUSS(data->asa[1]);
-	data->raw_to_gauss[2] = RAW_TO_GAUSS(data->asa[2]);
+	if (data->chipset == AK8963) {
+		/*
+		 * H range is +-8190 and magnetometer range is +-4912.
+		 * So HuT using the above explanation for 8975,
+		 * 4912/8190 = ~ 6/10.
+		 * So the Hadj should use 6/10 instead of 3/10.
+		 */
+		data->raw_to_gauss[0] = RAW_TO_GAUSS_8963(data->asa[0]);
+		data->raw_to_gauss[1] = RAW_TO_GAUSS_8963(data->asa[1]);
+		data->raw_to_gauss[2] = RAW_TO_GAUSS_8963(data->asa[2]);
+	} else {
+		data->raw_to_gauss[0] = RAW_TO_GAUSS_8975(data->asa[0]);
+		data->raw_to_gauss[1] = RAW_TO_GAUSS_8975(data->asa[1]);
+		data->raw_to_gauss[2] = RAW_TO_GAUSS_8975(data->asa[2]);
+	}
 
 	return 0;
 }
@@ -499,6 +519,9 @@ static int ak8975_probe(struct i2c_client *client,
 	data->eoc_gpio = eoc_gpio;
 	data->eoc_irq = 0;
 
+	data->chipset = (enum asahi_compass_chipset)(id->driver_data);
+	dev_dbg(&client->dev, "Asahi compass chip %s\n", id->name);
+
 	/* Perform some basic start-of-day setup of the device. */
 	err = ak8975_setup(client);
 	if (err < 0) {
@@ -552,7 +575,8 @@ static int ak8975_remove(struct i2c_client *client)
 }
 
 static const struct i2c_device_id ak8975_id[] = {
-	{"ak8975", 0},
+	{"ak8975", AK8975},
+	{"ak8963", AK8963},
 	{}
 };