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 <zhonghui...@linux.intel.com>
---
 drivers/i2c/i2c-core.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index ba8eb08..72d5466 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -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

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