i2c: enable i2c adapter to suspend/resume asynchronously

Now, PM core supports asynchronous suspend/resume mode for devices during system suspend/resume, and the power state transition of one device may be completed in separate kernel thread. PM core ensures all power state transition dependency between devices. This patch enables i2c adapters to suspend/resume asynchronously. This will take advantage of multicore and improve system suspend/resume speed. After enabling all i2c devices, i2c adapters and i2c controllers on ASUS T100TA tablet, the system suspend-to-idle time is reduced to about 510ms from 750ms, and the system resume time is reduced to about 790ms from 900ms.

Signed-off-by Zhonghui Fu <[email protected]>

---
 drivers/i2c/i2c-core.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

drivers/i2c/i2c-core.c +2 -1

index ba8eb08..72d5466 100644
@@ -1564,6 +1564,8 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
 
 	pm_runtime_no_callbacks(&adap->dev);
 
+	device_enable_async_suspend(&adap->dev);
+
 #ifdef CONFIG_I2C_COMPAT
 	res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
 				       adap->dev.parent);
-- 1.7.1