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    SubjectRe: pm runtime and system suspend resume
    On Wed, 20 Jun 2012, chao xie wrote:

    > >> It seems work well, but i have question about the suspend/resume of
    > >> device. When the whole system will go to deep idle, and it will
    > >> suspend the devices. for the function do device suspend
    > >> __device_suspend,
    > >
    > > What source file is that function in?
    > >
    >
    > The function is located at drivers/base/power/main.c
    >
    > >> it will call pm_runtime_get_noresume(dev). As i
    > >> think it will make the device not do runtime suspend any more. Is that
    > >> correct?
    > >
    > > It sounds wrong. Why would a suspend routine do that?
    > >
    >
    > I do knot know, but the code is there.

    Okay, now I understand your question. The problem is that system
    suspend uses a separate mechanism from runtime suspend, and we don't
    want the two things to happen at the same time. Therefore
    __device_suspend does a get_noresume in order to prevent runtime
    suspend from occurring in the middle of a system suspend.

    > >> There is the question, how device driver handle the logic surrounds
    > >> it? I want to add pm_runtime_put_sync in dev->driver->pm->suspend
    > >> function, and pm_runtime_get_sync in dev->driver->pm->resume.
    > >
    > > You must not do that. If you do, your driver will hang.
    > >
    >
    > why it will hang?

    Sorry, I misunderstood your question. It will not hang. But why do
    you want to add those calls?

    > >> Because
    > >> __device_suspend increase the usage_count, pm_runtime_put_sync will
    > >> not do real work.
    > >> So is that right that i directly call pm_runtime_suspend in
    > >> dev->driver->pm->suspend and pm_runtime_resume in
    > >> dev->driver->pm->resume?

    No, don't call pm_runtime_suspend. Just call your driver's
    runtime_suspend routine directly. Same for resume.

    > Finally the real question is who will deal with the dev->pm_domain?
    > when system go to sleep.

    The __device_suspend routine in drivers/base/main.c uses
    dev->pm_domain.

    > The driver will use pm_runtime_get/put to deal with dev->pm_domain
    > when it want to work or is in idle. Then when system go to sleep, the
    > driver need care about dev->pm_domain too.
    > Usally, dev->pm_domain is a easy way to handle the difference SOCs
    > with same device IP. For example, USB. Many vendor may have same usb
    > IP but difference phy and clock configuration. putting these stuff
    > into dev->pm_domain can make driver be shared by different SOCs.

    Alan Stern



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