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Hi Rafael, 1) I have question on system resume that e.g. in device driver let us say for example structure is defined global, e.g. struct dev { int a; } dev_t; this structure is global. Now during system suspend, suppose the value of dev_t.a =2; So when the resume happens, will the dev_t.a will remain the same i.e. 2? 2) During the system suspend, if the system hibernates, then the message sent from power management core to all drivers is PMSG_HIBERNATE and if system suspends to ram, then message sent from power management core to all drivers is PMSG_SUSPEND. correct me if I am wrong. Regards Raj > From: rjw@xxxxxxx > To: rajkumar278@xxxxxxxxxxx > Subject: Re: Question about hibernation > Date: Fri, 8 Oct 2010 21:31:48 +0200 > CC: linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx > > 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 |
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