[PATCH 3/3] iio: ak8975: Added autodetect feature for ACPI

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Using i2c auto detect feature and auto device creation feature,
enumerate ak8975 device, by checking their presence.
This is needed because when this device sits behind an i2c mux, there
is no way to define i2c mux in ACPI. This will enable ak8975 on
windows based tablets/laptops running Linux when connected via a mux.
Since DT model already can define an i2c mux and devices connected to
it, this feature is only enabled for ACPI.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
---
 drivers/iio/magnetometer/ak8975.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c
index 0d10a4b..c3455bd 100644
--- a/drivers/iio/magnetometer/ak8975.c
+++ b/drivers/iio/magnetometer/ak8975.c
@@ -820,6 +820,36 @@ static const struct i2c_device_id ak8975_id[] = {
 
 MODULE_DEVICE_TABLE(i2c, ak8975_id);
 
+#if defined(CONFIG_ACPI)
+static int ak8975_detect(struct i2c_client *temp_client,
+			 struct i2c_board_info *info)
+{
+	struct i2c_adapter *adapter;
+	int i, j;
+	int ret;
+
+	/* autodetect only when we are behind a mux */
+	adapter = i2c_parent_is_i2c_adapter(temp_client->adapter);
+	if (!adapter)
+		return -ENODEV;
+
+	for (i = 0; i < AK_MAX_TYPE; ++i) {
+		ret = ak8975_who_i_am(temp_client, i);
+		if (ret >= 0) {
+			for (j = 0; j < ARRAY_SIZE(ak8975_id) - 1; ++j) {
+				if (i == (int)ak8975_id[j].driver_data) {
+					strlcpy(info->type, ak8975_id[j].name,
+						I2C_NAME_SIZE);
+					return 0;
+				}
+			}
+		}
+	}
+
+	return -ENODEV;
+}
+#endif
+
 static const struct of_device_id ak8975_of_match[] = {
 	{ .compatible = "asahi-kasei,ak8975", },
 	{ .compatible = "ak8975", },
@@ -841,6 +871,11 @@ static struct i2c_driver ak8975_driver = {
 	},
 	.probe		= ak8975_probe,
 	.id_table	= ak8975_id,
+#if defined(CONFIG_ACPI)
+	.class		= I2C_CLASS_HWMON,
+	.address_list	= I2C_ADDRS(0x0C, 0x0D, 0x0E, 0x0F),
+	.detect		= ak8975_detect,
+#endif
 };
 module_i2c_driver(ak8975_driver);
 
-- 
1.9.3