Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend

From	"Rafael J. Wysocki" <rafael@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend
Date	2015-09-09 02:00 +0200
Message-ID	<q6AXT-2Ia-1@gated-at.bofh.it> (permalink)
References	(1 earlier) <q6bG9-8hQ-1@gated-at.bofh.it> <q6fJM-5Z2-5@gated-at.bofh.it> <q6lFw-63O-17@gated-at.bofh.it> <q6y9I-76u-17@gated-at.bofh.it> <q6zyN-Of-1@gated-at.bofh.it>
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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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Thread

[RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend Irina Tirdea <irina.tirdea@intel.com> - 2015-09-07 22:50 +0200
  Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-07 23:00 +0200
    RE: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend "Tirdea, Irina" <irina.tirdea@intel.com> - 2015-09-08 03:20 +0200
      Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Oliver Neukum <oneukum@suse.com> - 2015-09-08 09:40 +0200
        Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-08 23:00 +0200
          Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Ulf Hansson <ulf.hansson@linaro.org> - 2015-09-09 00:30 +0200
            Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-09 02:00 +0200
              Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Octavian Purdila <octavian.purdila@intel.com> - 2015-09-09 13:20 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-09 14:30 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Oliver Neukum <oneukum@suse.com> - 2015-09-09 16:00 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Octavian Purdila <octavian.purdila@intel.com> - 2015-09-09 17:10 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-09 22:00 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Oliver Neukum <oneukum@suse.com> - 2015-09-10 11:50 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Pavel Machek <pavel@ucw.cz> - 2015-09-21 14:30 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-09 17:30 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-09 22:10 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Colin Cross <ccross@google.com> - 2015-09-09 22:20 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Pavel Machek <pavel@ucw.cz> - 2015-09-21 14:40 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-21 16:40 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2015-09-21 18:20 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-21 18:40 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2015-09-21 19:00 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-21 19:40 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2015-09-21 20:10 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-21 22:10 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Dmitry Torokhov <dmitry.torokhov@gmail.com> - 2015-09-21 23:00 +0200
                Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Pavel Machek <pavel@ucw.cz> - 2015-09-21 22:30 +0200
      RE: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-08 16:50 +0200
        Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing runtime suspend "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-08 16:50 +0200
          Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-08 17:10 +0200
            Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend "Rafael J. Wysocki" <rafael@kernel.org> - 2015-09-08 22:30 +0200
              Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-09 17:30 +0200
        Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Oliver Neukum <oneukum@suse.com> - 2015-09-09 08:30 +0200
          Re: [RFC PATCH] PM / Runtime: runtime: Add sysfs option for forcing  runtime suspend Alan Stern <stern@rowland.harvard.edu> - 2015-09-09 16:40 +0200

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