Re: Question about hibernation

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Friday, October 08, 2010, you wrote:
> 
> Hi Rafael,

Hi,

> I am working on device driver whose some part is user space and some part is kernel space. So the user space part
> of the driver provides interface to user space applications. 
> 1) Now, Suppose some user space is application is going on which is accessing the user space driver and user space driver
> scheduled some jobs to kernel space, Now suppose system hibernation start, since it freezes all the user space processes
> so suppose jobs are not completed yet which are scheduled to kernel space by user space.
>  
> when the kernel space device driver completes the jobs and gives the notification to user space driver, since user space
> process is already frozen, so there will be problem if we suspend the driver using suspend and resume.
>  
> right?

Yes, there's going to be a problem if the driver is not prepared to handle such situations.

Depending of the particular case, one possible approach is to use a PM notifier
as described in Documentation/power/notifiers.txt.

> 2) The other point I was seeing, when the power management core freezes all the processes before suspending and resuming
> devices, it will take some time for freezing and after that if some device driver refuses to suspend, then it will again resume
> the whole processes, so latency time be more. right?

Yes, it works as described.

> 3) Next question is regarding the kernel space threads, when these are frozen during suspend/hibernation?

They are frozen immediately after user space has been frozen, but only a
handful of kernel threads are frozen.

Thanks,
Rafael