i2c: Provide compatibility links for i2c adapters

Some user-space applications may be relying on i2c adapters showing up
as class devices in sysfs. Provide compatibility links for them for
the time being. We will remove them after a long transition period.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>

2 files changed, 40 insertions, 1 deletions

diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 711ca08ab776..d7ece131b4f4 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -27,6 +27,14 @@ config I2C_BOARDINFO
         boolean
         default y
 
+config I2C_COMPAT
+        boolean "Enable compatibility bits for old user-space"
+        default y
+        help
+          Say Y here if you intend to run lm-sensors 3.1.1 or older, or any
+          other user-space package which expects i2c adapters to be class
+          devices. If you don't know, say Y.
+
 config I2C_CHARDEV
         tristate "I2C device interface"
         help
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index a18a251dabf9..8d80fceca6a4 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -538,6 +538,10 @@ static struct device_type i2c_adapter_type = {
         .release        = i2c_adapter_dev_release,
 };
 
+#ifdef CONFIG_I2C_COMPAT
+static struct class_compat *i2c_adapter_compat_class;
+#endif
+
 static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
 {
         struct i2c_devinfo      *devinfo;
@@ -595,6 +599,14 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
 
         dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);
 
+#ifdef CONFIG_I2C_COMPAT
+        res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
+                                       adap->dev.parent);
+        if (res)
+                dev_warn(&adap->dev,
+                         "Failed to create compatibility class link\n");
+#endif
+
         /* create pre-declared device nodes */
         if (adap->nr < __i2c_first_dynamic_bus_num)
                 i2c_scan_static_board_info(adap);
@@ -773,6 +785,11 @@ int i2c_del_adapter(struct i2c_adapter *adap)
            checking the returned value. */
         res = device_for_each_child(&adap->dev, NULL, __unregister_client);
 
+#ifdef CONFIG_I2C_COMPAT
+        class_compat_remove_link(i2c_adapter_compat_class, &adap->dev,
+                                 adap->dev.parent);
+#endif
+
         /* clean up the sysfs representation */
         init_completion(&adap->dev_released);
         device_unregister(&adap->dev);
@@ -978,12 +995,23 @@ static int __init i2c_init(void)
         retval = bus_register(&i2c_bus_type);
         if (retval)
                 return retval;
+#ifdef CONFIG_I2C_COMPAT
+        i2c_adapter_compat_class = class_compat_register("i2c-adapter");
+        if (!i2c_adapter_compat_class) {
+                retval = -ENOMEM;
+                goto bus_err;
+        }
+#endif
         retval = i2c_add_driver(&dummy_driver);
         if (retval)
-                goto bus_err;
+                goto class_err;
         return 0;
 
+class_err:
+#ifdef CONFIG_I2C_COMPAT
+        class_compat_unregister(i2c_adapter_compat_class);
 bus_err:
+#endif
         bus_unregister(&i2c_bus_type);
         return retval;
 }
@@ -991,6 +1019,9 @@ bus_err:
 static void __exit i2c_exit(void)
 {
         i2c_del_driver(&dummy_driver);
+#ifdef CONFIG_I2C_COMPAT
+        class_compat_unregister(i2c_adapter_compat_class);
+#endif
         bus_unregister(&i2c_bus_type);
 }