[RFC PATCH 1/2] i2c: prepare runtime PM support for I2C client devices

[Mika Westerberg <mika.westerberg@linux.intel.com>]

From: Aaron Lu <aaron.lu@intel.com>

This patch adds runtime PM support for the I2C bus in a similar way that
has been done for PCI bus already. This means that the I2C bus core
prepares runtime PM for a client device just before a driver is about to be
bound to it. Devices that are not bound to any driver are not prepared for
runtime PM.

In order to take advantage of this runtime PM support, the client device
driver needs drop the device runtime PM reference count by calling
pm_runtime_put() in its ->probe() callback and possibly implement rest of
the runtime PM callbacks.

However, this does not yet make runtime PM happen for the device, it has to
be explicitly allowed from userspace per each I2C client device. The
reason for this is that things like HID over I2C might not work as smoothly
when runtime PM is active. So we leave it to the user to balance between
performance and power efficiency.

User can allow runtime PM for the client device by running:

	# echo auto > /sys/bus/i2c/devices/<device>/power/control

and it can be forbidden again by:

	# echo on > /sys/bus/i2c/devices/<device>/power/control

Status of the device can be monitored by reading files under the device
power directory.

If the driver doesn't support runtime PM (like most of the existing I2C
client drivers), the device in question is regarded as being runtime PM
active and powered on.

The patch adds also runtime PM support for the adapter device because it is
needed to be able to runtime power manage the I2C controller device. The
adapter device is handled along with the I2C controller device (it uses
pm_runtime_no_callbacks()).

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
---
 drivers/i2c/i2c-core.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 3d44292..8fad5ac 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -254,11 +254,34 @@ static int i2c_device_probe(struct device *dev)
 					client->flags & I2C_CLIENT_WAKE);
 	dev_dbg(dev, "probe\n");
 
+	/* Make sure the adapter is active */
+	pm_runtime_get_sync(&client->adapter->dev);
+
+	/*
+	 * Enable runtime PM for the client device. If the client wants to
+	 * participate on runtime PM it should call pm_runtime_put() in its
+	 * probe() callback.
+	 *
+	 * User still needs to allow the PM runtime before it can actually
+	 * happen.
+	 */
+	pm_runtime_forbid(&client->dev);
+	pm_runtime_get_noresume(&client->dev);
+	pm_runtime_set_active(&client->dev);
+	pm_runtime_enable(&client->dev);
+
 	status = driver->probe(client, i2c_match_id(driver->id_table, client));
 	if (status) {
 		client->driver = NULL;
 		i2c_set_clientdata(client, NULL);
+
+		pm_runtime_disable(&client->dev);
+		pm_runtime_set_suspended(&client->dev);
+		pm_runtime_put_noidle(&client->dev);
 	}
+
+	pm_runtime_put(&client->adapter->dev);
+
 	return status;
 }
 
@@ -271,6 +294,8 @@ static int i2c_device_remove(struct device *dev)
 	if (!client || !dev->driver)
 		return 0;
 
+	pm_runtime_get_sync(&client->adapter->dev);
+
 	driver = to_i2c_driver(dev->driver);
 	if (driver->remove) {
 		dev_dbg(dev, "remove\n");
@@ -283,6 +308,13 @@ static int i2c_device_remove(struct device *dev)
 		client->driver = NULL;
 		i2c_set_clientdata(client, NULL);
 	}
+
+	/* Undo the runtime PM done in i2c_probe() */
+	pm_runtime_disable(&client->dev);
+	pm_runtime_set_suspended(&client->dev);
+	pm_runtime_put_noidle(&client->dev);
+
+	pm_runtime_put(&client->adapter->dev);
 	return status;
 }
 
@@ -294,8 +326,11 @@ static void i2c_device_shutdown(struct device *dev)
 	if (!client || !dev->driver)
 		return;
 	driver = to_i2c_driver(dev->driver);
-	if (driver->shutdown)
+	if (driver->shutdown) {
+		pm_runtime_get_sync(&client->adapter->dev);
 		driver->shutdown(client);
+		pm_runtime_put(&client->adapter->dev);
+	}
 }
 
 #ifdef CONFIG_PM_SLEEP
@@ -1263,6 +1298,15 @@ exit_recovery:
 	bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
 	mutex_unlock(&core_lock);
 
+	/*
+	 * Make sure the adapter runtime PM follows the parent device (the
+	 * host controller) so that we can suspend it once there aren't any
+	 * active clients anymore.
+	 */
+	pm_runtime_set_active(&adap->dev);
+	pm_runtime_no_callbacks(&adap->dev);
+	pm_runtime_enable(&adap->dev);
+
 	return 0;
 
 out_list:
@@ -1427,6 +1471,8 @@ void i2c_del_adapter(struct i2c_adapter *adap)
 		return;
 	}
 
+	pm_runtime_disable(&adap->dev);
+
 	/* Tell drivers about this removal */
 	mutex_lock(&core_lock);
 	bus_for_each_drv(&i2c_bus_type, NULL, adap,
-- 
1.8.4.rc2