Hi Ran, Please find my replies as follows:-

How does the driver invokes moving to idle state ?

The driver uses numerous apis to send its device to idle state. Some of them are as follows:- 1. pm_runtime_put/pm_runtime_put_sync - which decreases the usage count and ultimately calls pm_runtime_idle. 2. pm_runtime_idle - which calls the corresponding driver->runtime_idle after checking the usage count 3. pm_request_idle - calls pm_runtime_idle Is it the same as

invoking runtime suspend by the driver ?

In some cases, eg In platform subsystem drivers , runtime_suspend gets called from runtime_idle. eg Refer drivers/base/platform.c, the runtime operations assigned are :- static const struct dev_pm_ops platform_dev_pm_ops = { .runtime_suspend = pm_generic_runtime_suspend, .runtime_resume = pm_generic_runtime_resume, .runtime_idle = pm_generic_runtime_idle, USE_PLATFORM_PM_SLEEP_OPS }; Here pm_generic_runtime_idle() after calling the driver specific runtime_idle api, calls pm_runtime_suspend --> pm_generic_runtime_suspend ---> driver specific runtime suspend call.

What is the difference between idle state to runtime suspend ?

I don't clearly understand the difference between idle state and runtime suspend as in case of most devices (eg platform devices, usb devices) , I see that runtime_idle eventually calls runtime_suspend. eg drivers/usb/core/usb.c , usb_runtime_idle() -----> pm_runtime_autosuspend()

Are you familiar with any character device example for using PM ?

Check drivers/usb/core/usb.c. Regards, Ayan Kumar Halder