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    SubjectRe: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend
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    Hi,

    On Wed, Sep 9, 2015 at 12:25 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
    > On 8 September 2015 at 22:56, Rafael J. Wysocki <rafael@kernel.org> wrote:
    >> On Tue, Sep 8, 2015 at 9:35 AM, Oliver Neukum <oneukum@suse.com> wrote:
    >>> On Tue, 2015-09-08 at 01:10 +0000, Tirdea, Irina wrote:
    >>
    >> [cut]
    >>
    >>>> this would work except for adding a sysfs attribute that would trigger
    >>>> a runtime suspend while ignoring usage count. Would that be a
    >>>> better direction?
    >>>
    >>> No. If we want this at all, we need a new callback to notify drivers
    >>> that user space is temporarily uninterested in a device. And the reverse
    >>> of course.
    >>> The power model is good. We must not assume that devices can be
    >>> suspended at will. If we do this at all, we ought to see it as giving
    >>> strong hints to drivers when a device can be considered idle.
    >>
    >> This is a good summary in my view.
    >>
    >> The only thing we can add, realistically, is an interface for user
    >> space to "kick" drivers to check if the devices they handle may be
    >> suspended at this point (or to run their ->runtime_idle callbacks
    >> IOW).
    >>
    >> That would be quite similar to autosuspend except that the "kick" will
    >> come from user space rather than from a timer function in the kernel.
    >
    > Apologize for interrupting the discussion!
    >
    > Unless I miss the point, I assumes the above is somewhat already
    > achievable via sysfs when changing the value of the auto-suspend
    > timeout, since it triggers a call to
    > pm_runtime_set_autosuspend_delay()...

    Well, from the initial comment in drivers/base/power/sysfs.c:

    *
    * NOTE: The autosuspend_delay_ms attribute and the autosuspend_delay
    * value are used only if the driver calls pm_runtime_use_autosuspend().
    *

    Some drivers don't do that and they would be the primary target
    audience for the new interface (if we agreed that it was useful after
    all).

    > Also, according to the discussion so far, it seems like we are on
    > agreement that we should really think twice when considering to extend
    > the sysfs interface for runtime PM.

    That certainly is correct and not limited to runtime PM. :-)

    > From the change-log/description to $subject patch, I fail to
    > understand *why* the regular runtime PM *autosuspend* feature isn't
    > sufficient. Perhaps Irina can elaborate more on the use case, to help
    > me get a better understanding of the issue!?

    My understanding is that the idea would be to trigger an attempt to
    suspend via a specific event (eg. lid closes) rather then via an
    inactivity timer.

    Thanks,
    Rafael


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