Mika Westerberg [off-list ref] writes:

On Thu, Sep 12, 2013 at 02:34:21PM -0700, Kevin Hilman wrote:

quoted

quoted

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index f32ca29..44374b4 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c

@@ -248,11 +248,30 @@ 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.
+	 */
+	pm_runtime_get_noresume(&client->dev);
+	pm_runtime_set_active(&client->dev);

Why the set_active here?

For hardware that is disabled/powered-off on startup, there will now be
a mismatch between the hardware state an the RPM core state.

The call to pm_runtime_get_noresume() should make sure that the device is
in active state (at least in state where it can access the bus) if I'm
understanding this right.

No, after _get_noresume(), nothing happens to the hardware.  It simply
increments the usecount.  From pm_runtime.h:

static inline void pm_runtime_get_noresume(struct device *dev)
{
	atomic_inc(&dev->power.usage_count);
}

So after the _get_noresume() and _set_active() you're very likely to
have a disconnect between the hardware state and what state RPM thinks
the hardware is in.

Kevin