mmc: enable mmc host device 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 timing dependency between devices. This patch enables mmc host device to suspend/resume asynchronously. This will take advantage of multicore and improve system suspend/resume speed. After enabling the mmc host and all their child devices to suspend/resume asynchronously on ASUS T100TA, the system suspend-to- idle time is reduced from 1645ms to 1114ms, and the system resume time is reduced from 940ms to 914ms.

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

---
Changes in v3:
- Add test result in commit message

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

drivers/mmc/core/host.c +1 -1

index da950c4..7222fd7 100644
@@ -339,6 +339,7 @@ struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
 	host->class_dev.parent = dev;
 	host->class_dev.class = &mmc_host_class;
 	device_initialize(&host->class_dev);
+	device_enable_async_suspend(&host->class_dev);
 
 	if (mmc_gpio_alloc(host)) {
 		put_device(&host->class_dev);
-- 1.7.1