i2c: Limit core locking to the necessary sections
Jean Delvare [Fri, 19 Jun 2009 14:58:19 +0000 (16:58 +0200)]
The i2c-core code tends to hold the core lock for longer than it
should. Limit locking to the necessary sections for both performance
and clarity. This is also a requirement to support I2C multiplexers in
the future.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Tested-by: Rodolfo Giometti <giometti@linux.it>
Cc: David Brownell <dbrownell@users.sourceforge.net>

drivers/i2c/i2c-core.c

index b1fd00d..a2f1cd3 100644 (file)
@@ -38,6 +38,9 @@
 #include "i2c-core.h"
 
 
+/* core_lock protects i2c_adapter_idr, and guarantees
+   that device detection, deletion of detected devices, and attach_adapter
+   and detach_adapter calls are serialized */
 static DEFINE_MUTEX(core_lock);
 static DEFINE_IDR(i2c_adapter_idr);
 
@@ -418,13 +421,13 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
        int res = 0, dummy;
 
        /* Can't register until after driver model init */
-       if (unlikely(WARN_ON(!i2c_bus_type.p)))
-               return -EAGAIN;
+       if (unlikely(WARN_ON(!i2c_bus_type.p))) {
+               res = -EAGAIN;
+               goto out_list;
+       }
 
        mutex_init(&adap->bus_lock);
 
-       mutex_lock(&core_lock);
-
        /* Set default timeout to 1 second if not already set */
        if (adap->timeout == 0)
                adap->timeout = HZ;
@@ -443,16 +446,18 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
                i2c_scan_static_board_info(adap);
 
        /* Notify drivers */
+       mutex_lock(&core_lock);
        dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
                                 i2c_do_add_adapter);
-
-out_unlock:
        mutex_unlock(&core_lock);
-       return res;
+
+       return 0;
 
 out_list:
+       mutex_lock(&core_lock);
        idr_remove(&i2c_adapter_idr, adap->nr);
-       goto out_unlock;
+       mutex_unlock(&core_lock);
+       return res;
 }
 
 /**
@@ -590,22 +595,25 @@ static int __unregister_client(struct device *dev, void *dummy)
 int i2c_del_adapter(struct i2c_adapter *adap)
 {
        int res = 0;
-
-       mutex_lock(&core_lock);
+       struct i2c_adapter *found;
 
        /* First make sure that this adapter was ever added */
-       if (idr_find(&i2c_adapter_idr, adap->nr) != adap) {
+       mutex_lock(&core_lock);
+       found = idr_find(&i2c_adapter_idr, adap->nr);
+       mutex_unlock(&core_lock);
+       if (found != adap) {
                pr_debug("i2c-core: attempting to delete unregistered "
                         "adapter [%s]\n", adap->name);
-               res = -EINVAL;
-               goto out_unlock;
+               return -EINVAL;
        }
 
        /* Tell drivers about this removal */
+       mutex_lock(&core_lock);
        res = bus_for_each_drv(&i2c_bus_type, NULL, adap,
                               i2c_do_del_adapter);
+       mutex_unlock(&core_lock);
        if (res)
-               goto out_unlock;
+               return res;
 
        /* Detach any active clients. This can't fail, thus we do not
           checking the returned value. */
@@ -619,7 +627,9 @@ int i2c_del_adapter(struct i2c_adapter *adap)
        wait_for_completion(&adap->dev_released);
 
        /* free bus id */
+       mutex_lock(&core_lock);
        idr_remove(&i2c_adapter_idr, adap->nr);
+       mutex_unlock(&core_lock);
 
        dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
 
@@ -627,9 +637,7 @@ int i2c_del_adapter(struct i2c_adapter *adap)
           added again */
        memset(&adap->dev, 0, sizeof(adap->dev));
 
- out_unlock:
-       mutex_unlock(&core_lock);
-       return res;
+       return 0;
 }
 EXPORT_SYMBOL(i2c_del_adapter);
 
@@ -674,16 +682,15 @@ int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
        if (res)
                return res;
 
-       mutex_lock(&core_lock);
-
        pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
 
        INIT_LIST_HEAD(&driver->clients);
        /* Walk the adapters that are already present */
+       mutex_lock(&core_lock);
        class_for_each_device(&i2c_adapter_class, NULL, driver,
                              __attach_adapter);
-
        mutex_unlock(&core_lock);
+
        return 0;
 }
 EXPORT_SYMBOL(i2c_register_driver);
@@ -721,14 +728,12 @@ static int __detach_adapter(struct device *dev, void *data)
 void i2c_del_driver(struct i2c_driver *driver)
 {
        mutex_lock(&core_lock);
-
        class_for_each_device(&i2c_adapter_class, NULL, driver,
                              __detach_adapter);
+       mutex_unlock(&core_lock);
 
        driver_unregister(&driver->driver);
        pr_debug("i2c-core: driver [%s] unregistered\n", driver->driver.name);
-
-       mutex_unlock(&core_lock);
 }
 EXPORT_SYMBOL(i2c_del_driver);