[PATCH 01/10] i2c: add and export of_get_i2c_adapter_by_node() interface

[Vladimir Zapolskiy]

of_find_i2c_adapter_by_node() call requires quite often missing
put_device(), and i2c_put_adapter() releases a device locked by
i2c_get_adapter() only. In general module_put(adapter->owner) and
put_device(dev) are not interchangeable.

This is a common error reproduction scenario as a result of the
misusage described above (for clearness this is run on iMX6 platform
with HDMI and I2C bus drivers compiled as kernel modules):

    root at mx6q:~# lsmod | grep i2c
    i2c_imx                10213  0
    root at mx6q:~# lsmod | grep dw_hdmi_imx
    dw_hdmi_imx             3631  0
    dw_hdmi                11846  1 dw_hdmi_imx
    imxdrm                  8674  3 dw_hdmi_imx,imx_ipuv3_crtc,imx_ldb
    drm_kms_helper        113765  5 dw_hdmi,imxdrm,imx_ipuv3_crtc,imx_ldb
    root at mx6q:~# rmmod dw_hdmi_imx
    root at mx6q:~# lsmod | grep i2c
    i2c_imx                10213  -1

                                 ^^^^^

    root at mx6q:~# rmmod i2c_imx
    rmmod: ERROR: Module i2c_imx is in use

To fix existing users of these interfaces and to avoid any further
confusion and misusage in future, add one more interface
of_get_i2c_adapter_by_node(), it is similar to i2c_get_adapter() in
sense that an I2C bus device driver found and locked by user can be
correctly unlocked by i2c_put_adapter().

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy at mentor.com>
---
The change is based on RFC http://www.spinics.net/lists/linux-i2c/msg20257.html

* added new exported function declaration in include/linux/i2c.h
* added put_device(dev) call right inside of_get_i2c_adapter_by_node()
* corrected authorship of the change

 drivers/i2c/i2c-core.c | 20 ++++++++++++++++++++
 include/linux/i2c.h    |  6 ++++++
 2 files changed, 26 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 069a41f..0d902ab 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -1356,6 +1356,26 @@ 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);
+
+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;
+
+	put_device(dev);
+
+	return adapter;
+}
+EXPORT_SYMBOL(of_get_i2c_adapter_by_node);
 #else
 static void of_i2c_register_devices(struct i2c_adapter *adap) { }
 #endif /* CONFIG_OF */
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index e83a738..87bb217 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -638,6 +638,7 @@ 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);
 
+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 +650,11 @@ 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 */
-- 
2.1.4