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    SubjectRe: [PATCH 1/3] PM / sleep: New flag to speed up suspend-resume of suspended devices
    Date
    On Tuesday, February 18, 2014 01:59:36 PM Ulf Hansson wrote:
    > On 17 February 2014 00:50, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
    > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    > >
    > > Currently, some subsystems (e.g. PCI and the ACPI PM domain) have to
    > > resume all runtime-suspended devices during system suspend, mostly
    > > because those devices may need to be reprogrammed due to different
    > > wakeup settings for system sleep and for runtime PM. However, at
    > > least in some cases, that isn't really necessary, because the wakeup
    > > settings may not be really different.
    > >
    > > The idea here is that subsystems should know whether or not it is
    > > necessary to reprogram a given device during system suspend and they
    > > should be able to tell the PM core about that. For this reason,
    > > modify the PM core so that if the .prepare() callback returns a
    > > positive value for certain device, the core will set a new
    > > power.fast_suspend flag for it. Then, if that flag is set, the core
    > > will skip all of the subsequent suspend callbacks for that device.
    > > It also will skip all of the system resume callbacks for the device
    > > during the subsequent system resume and pm_request_resume() will be
    > > executed to trigger a runtime PM resume of the device after the
    > > system device resume sequence has been finished.
    > >
    > > However, since parents may need to be resumed so that their children
    > > can be reprogrammed, make the PM core clear power.fast_suspend for
    > > devices whose children don't have power.fast_suspend set (the
    > > power.ignore_children flag doesn't matter here, because a parent
    > > whose children are normally ignored for runtime PM may still need to
    > > be accessible for their children to be prepare for system suspend
    > > properly).
    > >
    > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    > > ---
    > > drivers/base/power/main.c | 49 +++++++++++++++++++++++++++++++---------------
    > > include/linux/pm.h | 1
    > > 2 files changed, 35 insertions(+), 15 deletions(-)
    > >
    > > Index: linux-pm/drivers/base/power/main.c
    > > ===================================================================
    > > --- linux-pm.orig/drivers/base/power/main.c
    > > +++ linux-pm/drivers/base/power/main.c
    > > @@ -478,7 +478,7 @@ static int device_resume_noirq(struct de
    > > TRACE_DEVICE(dev);
    > > TRACE_RESUME(0);
    > >
    > > - if (dev->power.syscore)
    > > + if (dev->power.syscore || dev->power.fast_suspend)
    > > goto Out;
    > >
    > > if (!dev->power.is_noirq_suspended)
    > > @@ -599,7 +599,7 @@ static int device_resume_early(struct de
    > > TRACE_DEVICE(dev);
    > > TRACE_RESUME(0);
    > >
    > > - if (dev->power.syscore)
    > > + if (dev->power.syscore || dev->power.fast_suspend)
    > > goto Out;
    > >
    > > if (!dev->power.is_late_suspended)
    > > @@ -724,6 +724,11 @@ static int device_resume(struct device *
    > > if (dev->power.syscore)
    > > goto Complete;
    > >
    > > + if (dev->power.fast_suspend) {
    > > + pm_request_resume(dev);
    > > + goto Complete;
    >
    > So, this will trigger an async request to runtime resume the device.
    >
    > At device_complete(), we do pm_runtime_put() to return the reference
    > we fetched at device_prepare(), thus likely causing the device to be
    > runtime suspended again. Is that the expected sequence you need? Could
    > you elaborate why?

    That pm_runtime_put() will not cause the device to be re-suspended,
    because it will be executed before the resume scheduled by the
    pm_request_resume() above.

    Thanks!

    --
    I speak only for myself.
    Rafael J. Wysocki, Intel Open Source Technology Center.


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