i2c: core: add of_get_i2c_adapter_by_node

This adds of_get_i2c_adapter_by_node which both finds and properly increments the adapter reference count.

This is different from of_find_i2c_device_by_node which does not increment the adapter reference counter.

---
 drivers/i2c/i2c-core.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

index 987c124..97caec6 100644
@@ -1347,6 +1347,26 @@ struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node *node)
     return i2c_verify_adapter(dev);
 }
 EXPORT_SYMBOL(of_find_i2c_adapter_by_node);
+
+/* must call put_device() when done with returned i2c_adapter device */
+struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node *node)
+{
+    struct device *dev;
+    struct i2c_adapter *adapter;
+
+    dev = bus_find_device(&i2c_bus_type, NULL, node,
+                of_dev_node_match);
+    if (!dev)
+        return NULL;
+
+    adapter = i2c_verify_adapter(dev);
+
+    if (adapter && !try_module_get(adapter->owner))
+        adapter = NULL;
+
+    return adapter;
+}
+EXPORT_SYMBOL(of_get_i2c_adapter_by_node);
 #else
 static void of_i2c_register_devices(struct i2c_adapter *adap) { }
 #endif /* CONFIG_OF */

Joshua Frkuska | Embedded Software Engineer
Mentor Embedded Software Division
Mentor Graphics Japan Co., ltd.

What is your use case? Which code will be using this function?

Hi Wolfram,

the usecase is to avoid double getting of a pointer to the wanted struct i2c_adapter with incrementing its user counter at once, now it is done in two stages, namely find adapter and get adapter:

------8<------

struct i2c_adapter *ddc;
int id;
...

- ddc = of_find_i2c_adapter_by_node(ddc_node);
- if (ddc) {
- id = i2c_adapter_id(dcc);
- dcc = i2c_get_adapter(id);
+ dcc = of_get_i2c_adapter_by_node(ddc);
+ if (dcc)
+ put_device(&ddc->dev);
put_device(&ddc->dev);
- }

...
i2c_put_adapter(ddc);

------8<------

Since i2c adapted is locked by client, it might have sense to add put_device() hidden inside of_get_i2c_adapter_by_node().

At the moment there is an intention to add clients in drivers/gpu/drm/*, who should lock i2c bus driver to sustain DDC lines.

By the way to the current version the correspondent change in include/linux/i2c.h is missing:

------8<------

index e83a738..555ad9c 100644
@@ -638,6 +638,9 @@ extern struct i2c_client

*of_find_i2c_device_by_node(struct device_node *node);
/* must call put_device() when done with returned i2c_adapter device */ extern struct i2c_adapter *of_find_i2c_adapter_by_node(struct
device_node *node);

+/* must call put_device() when done with returned i2c_adapter device */ +extern struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node *node);
+
#else

static inline struct i2c_client *of_find_i2c_device_by_node(struct
device_node *node)
@@ -649,6 +652,11 @@ static inline struct i2c_adapter *of_find_i2c_adapter_by_node(struct device_node
{
return NULL;
}
+
+static inline struct i2c_adapter *of_get_i2c_adapter_by_node(struct device_node *node)
+{
+ return NULL;
+}
#endif /* CONFIG_OF */

#endif /* _LINUX_I2C_H */

------8<------

--
With best wishes,
Vladimir