[PATCH v2 2/3] i2c: core: Add new i2c_acpi_new_device helper function

[Hans de Goede <hdegoede@redhat.com>]

By default the i2c subsys creates an i2c-client for the first I2cSerialBus
resource of an acpi_device, but some acpi_devices have multiple
I2cSerialBus resources and the driver may need access to the others.

This commit adds a new i2c_acpi_new_device function which can be used by
drivers to create an i2c-client for any (other) I2cSerialBus resource of
an acpi_device.

Note that the other resources may even be on a different i2c bus, so just
retrieving the client address is not enough.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/i2c/i2c-core.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/i2c.h    |  5 +++++
 2 files changed, 53 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 32b58fb..8ddd55b 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -421,6 +421,54 @@ static int i2c_acpi_notify(struct notifier_block *nb, unsigned long value,
 static struct notifier_block i2c_acpi_notifier = {
 	.notifier_call = i2c_acpi_notify,
 };
+
+/**
+ * i2c_acpi_new_device - Create i2c client for the Nth acpi resource of dev
+ * @dev:     Device owning the acpi resources to get the client from
+ * @index:   Index of acpi resource to get 
+ *
+ * By default the i2c subsys creates an i2c-client for the first I2cSerialBus
+ * resource of an acpi_device, but some acpi_devices have multiple
+ * I2cSerialBus resources and the driver may need access to the others.
+ * This function can be used by drivers to create an i2c-client for any
+ * resource of an acpi_device.
+ *
+ * Returns a pointer to the new i2c-client, or NULL if the resource or
+ * adapter were not found.
+ */
+struct i2c_client *i2c_acpi_new_device(struct device *dev, int index)
+{
+	struct i2c_acpi_lookup lookup;
+	struct i2c_board_info info;
+	struct i2c_adapter *adapter;
+	struct acpi_device *adev;
+	LIST_HEAD(resource_list);
+	int ret;
+
+	adev = ACPI_COMPANION(dev);
+	if (!adev)
+		return NULL;
+
+	memset(&info, 0, sizeof(info));
+	memset(&lookup, 0, sizeof(lookup));
+	lookup.info = &info;
+	lookup.device_handle = acpi_device_handle(adev);
+	lookup.index = index;
+
+	ret = acpi_dev_get_resources(adev, &resource_list,
+				     i2c_acpi_fill_info, &lookup);
+	acpi_dev_free_resource_list(&resource_list);
+
+	if (ret < 0 || !info.addr)
+		return NULL;
+
+	adapter = i2c_acpi_find_adapter_by_handle(lookup.adapter_handle);
+	if (!adapter)
+		return NULL;
+
+	return i2c_new_device(adapter, &info);
+}
+EXPORT_SYMBOL_GPL(i2c_acpi_new_device);
 #else /* CONFIG_ACPI */
 static inline void i2c_acpi_register_devices(struct i2c_adapter *adap) { }
 extern struct notifier_block i2c_acpi_notifier;
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 6b18352..369ebfa 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -824,11 +824,16 @@ static inline const struct of_device_id
 
 #if IS_ENABLED(CONFIG_ACPI)
 u32 i2c_acpi_find_bus_speed(struct device *dev);
+struct i2c_client *i2c_acpi_new_device(struct device *dev, int index);
 #else
 static inline u32 i2c_acpi_find_bus_speed(struct device *dev)
 {
 	return 0;
 }
+static inline struct i2c_client *i2c_acpi_new_device(struct device *d, int i)
+{
+	return NULL;
+}
 #endif /* CONFIG_ACPI */
 
 #endif /* _LINUX_I2C_H */
-- 
2.9.3