Any char device example for runtime PM ?

[Ran Shalit]

On Sun, Sep 14, 2014 at 7:45 PM, Peter Teoh <htmldeveloper at gmail.com> wrote:
>
>
> 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

 Hi Peter,

Thanks very much for the time,
Your answer makes a lot of sense actually.
I gave you the requirement I got AS-IS, and some of the difficulties I
have, partly stem from the things you meantion in your answer. After
this delving and research into this hugh issue of PM, I will
defenitely return with feedback about these requirements.

I would like to use your knowledge if I may. Is it possible to use
scheme b only, i.e. configure it all in low level (HW registers) and
not to use any linux mechanism ?

Thanks,
Ran