suspend/resume PM criterion for application

[Ran Shalit]

On Thu, Sep 11, 2014 at 8:32 AM, AYAN KUMAR HALDER <ayankumarh at gmail.com> wrote:
> On Thu, Sep 11, 2014 at 12:55 AM,  <Valdis.Kletnieks at vt.edu> wrote:
>> On Wed, 10 Sep 2014 21:58:48 +0300, Ran Shalit said:
>>
>>> 1. How can I make a process to notice this inactivity ? Do you think
>>> it can be implemented by some periodic process who check if there is
>>> activity ? It returns to the original question I raised, that I will
>>> use some periodic process who checks maybe cpu load or something like
>>> that. What do you think ?
>>
>> That's going to depend on your system and what processes are running.
>>
>> You may have an MP3 player going that doesn't take much CPU at all - but
>> shutting down because the user hasn't hit a button in 47 minutes will probably
>> irritate the user no end.  Or there may be a screensaver running that takes
>> twice as much CPU as the MP3 player, but is totally OK on the system
>> suspending whenever the rest of the system wants it.
>>
>> You're going to have to look at your system design, and decide for yourself
>> what the criteria are.
>
> Please correct me if my understanding is wrong:-
>
> I believe that autosuspend feature (for system suspend) is not present
> in kernel. I believe that there is no feature in kernel which checks
> for system ( cpu, devices) inactivity and suspends the entire system.
> System suspend is caused when :-
> 1. the user issues a command
> 2. The system receives some interrupt or event (lid closing event)
> 3. There is an external process which monitors system inactivity and
> suspends the system.
>
> For runtime suspend of a device, I believe it is the driver who has
> the complete responsibility to decide when to suspend the device or
> resume it.  The driver can take this decision on user intervention (eg
> when user writes to   /sys/devices/<my-device>/power/* ) or when the
> driver has completed servicing an interrupt and feels it has nothing
> more to do, etc

Thanks Vlaid, Ayan,

I am a bit yet struggling for couple of days on this PM issue, and I
would appreciate your continous advise.
The system requirement I have is as following:
1. make everything as automatic as possible , so that there won't be
any need to add any userspace application for the matter.
2. wakeup from all relevant wakeup sources
3. should not use sysfs (it should be disabled from kernel)
4. platform is OMAP3530.

Now, As I understand thus far, I have the following options (
requirement 3 above I will ignore, don't know how to handle it yet,
and assume for meanwhile that I have sysfs) :
1. use suspend scheme (no runtime PM)
    1.a. create some kernel thread who check cpu load and will decide
to disable system only if its below some minimum threshold (which
should indicate no activity)
    1.b. initialize all HW interrupts (gpio, uart, etc) as wakeup sources
    with this scheme only this thread is responsible for the suspend,
and there is no use of the runtime PM, right ?

2. use runtime PM scheme :
    With this scheme I don't understand how some device will wake the
system , or doesn't it need to  ? If a driver wakes up maybe it need
to deliver some info to system    ?

I think option 1 is also easier to support, what do you think about both ?

Thanks!!
Ran