Re: [PATCH 1/2] i2c: implement i2c_verify_adapter

From: Stephen Warren <redacted>

This converts a struct device * to a struct i2c_adapter * while verifying
that the device really is an I2C adapter. Just like i2c_verify_client.

Signed-off-by: Stephen Warren <redacted>
---
 drivers/i2c/i2c-core.c |   17 +++++++++++++++++
 include/linux/i2c.h    |    1 +
 2 files changed, 18 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index feb7dc3..a6ad32b 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c

@@ -772,6 +772,23 @@ struct device_type i2c_adapter_type = {
 };
 EXPORT_SYMBOL_GPL(i2c_adapter_type);
 
+/**
+ * i2c_verify_adapter - return parameter as i2c_adapter or NULL
+ * @dev: device, probably from some driver model iterator
+ *
+ * When traversing the driver model tree, perhaps using driver model
+ * iterators like @device_for_each_child(), you can't assume very much
+ * about the nodes you find.  Use this function to avoid oopses caused
+ * by wrongly treating some non-I2C device as an i2c_adapter.
+ */
+struct i2c_adapter *i2c_verify_adapter(struct device *dev)
+{
+	return (dev->type == &i2c_adapter_type)
+			? to_i2c_adapter(dev)
+			: NULL;
+}
+EXPORT_SYMBOL(i2c_verify_adapter);
+
 #ifdef CONFIG_I2C_COMPAT
 static struct class_compat *i2c_adapter_compat_class;
 #endif

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 195d8b3..b66cb60 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h

@@ -232,6 +232,7 @@ struct i2c_client {
 #define to_i2c_client(d) container_of(d, struct i2c_client, dev)
 
 extern struct i2c_client *i2c_verify_client(struct device *dev);
+extern struct i2c_adapter *i2c_verify_adapter(struct device *dev);
 
 static inline struct i2c_client *kobj_to_i2c_client(struct kobject *kobj)
 {