Any char device example for runtime PM ?

[Peter Teoh]

On Sat, Sep 13, 2014 at 3:50 PM, Ran Shalit <ranshalit at gmail.com> wrote:

> On Sat, Sep 13, 2014 at 4:14 AM, Peter Teoh <htmldeveloper at gmail.com>
> wrote:
> > please elaborate your requirements.   char dev is for I/O to hardware.
>  but
> > runtime PM is for hibernating machine.   what is the connection u trying
> to
> > achieve?
> >
> > On Mon, Sep 8, 2014 at 1:22 PM, Ran Shalit <ranshalit at gmail.com> wrote:
> >>
> >> Hello,
> >>
> >> Is there any character device example using runtime PM available ?
> >> It is most helpful,
> >>
> Hi,
>
> Some of the drivers I'm using are char devices, while I only saw
> platform device registration for runtime PM, so my question stem from
> this.
>
> As to the system requirement I have, it 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 this 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 periodic 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    ?
>
>
as a general comment, your requirement for PM sounds weird.

a.   normally, the linux kernel has its own PM protocol....and it governs
which devices to saves states, and restore it later.....there is a
hierarchy of calls to be made.   and it is a complex daisy chain from
devices to higher logical level.   but yours never seem to mention or plan
to integrate to this infrastructure?

b.   hardware PM (sorry, i am a software guy...may be wrong) for
microcontroller/CPU normally means different states resulting in different
external PINs being disable, and for the least powered state only one or
two pins are available to wake up the CP/microcontroller.   but when u
mentioned so many pins are potential wake up source......then it is not
powered down at all.

i am being vague and brief, not to waste time, as this is a big topic,
sorry.



-- 
Regards,
Peter Teoh
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