From: Ulf Hansson <ulf.hansson@linaro.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Linux PM <linux-pm@vger.kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Alan Stern <stern@rowland.harvard.edu>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux ACPI <linux-acpi@vger.kernel.org>,
Linux PCI <linux-pci@vger.kernel.org>,
Linux Documentation <linux-doc@vger.kernel.org>,
Mika Westerberg <mika.westerberg@linux.intel.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Kevin Hilman <khilman@kernel.org>
Subject: Re: [PATCH v2 1/6] PM / core: Add LEAVE_SUSPENDED driver flag
Date: Tue, 14 Nov 2017 17:07:59 +0100 [thread overview]
Message-ID: <CAPDyKFr4DgVdKtf=G1vUy=Si0nSTECsrWoqB+z9UCQHS8DuwcQ@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0i4yFGyqAZ6QqG7q1_xNfjMNHkPk3o0WuBvwKFeM2nXeg@mail.gmail.com>
On 11 November 2017 at 00:45, Rafael J. Wysocki <rafael@kernel.org> wrote:
> On Fri, Nov 10, 2017 at 10:09 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On 8 November 2017 at 14:25, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>
>>> Define and document a new driver flag, DPM_FLAG_LEAVE_SUSPENDED, to
>>> instruct the PM core and middle-layer (bus type, PM domain, etc.)
>>> code that it is desirable to leave the device in runtime suspend
>>> after system-wide transitions to the working state (for example,
>>> the device may be slow to resume and it may be better to avoid
>>> resuming it right away).
>>>
>>> Generally, the middle-layer code involved in the handling of the
>>> device is expected to indicate to the PM core whether or not the
>>> device may be left in suspend with the help of the device's
>>> power.may_skip_resume status bit. That has to happen in the "noirq"
>>> phase of the preceding system suspend (or analogous) transition.
>>> The middle layer is then responsible for handling the device as
>>> appropriate in its "noirq" resume callback which is executed
>>> regardless of whether or not the device may be left suspended, but
>>> the other resume callbacks (except for ->complete) will be skipped
>>> automatically by the core if the device really can be left in
>>> suspend.
>>
>> I don't understand the reason to why you need to skip invoking resume
>> callbacks to achieve this behavior, could you elaborate on that?
>
> The reason why it is done this way is because that takes less code and
> is easier (or at least less error-prone, because it avoids repeating
> patterns in middle layers).
>
> Note that the callbacks only may be skipped by the core if the middle
> layer has set power.skip_resume for the device (or if the core is
> handling it in patch [5/6], but that's one more step ahead still).
>
>> Couldn't the PM domain or the middle-layer instead decide what to do?
>
> They still can, the whole thing is a total opt-in.
>
> But to be constructive, do you have any specific examples in mind?
See more below.
>
>> To me it sounds a bit prone to errors by skipping callbacks from the
>> PM core, and I wonder if the general driver author will be able to
>> understand how to use this flag properly.
>
> This has nothing to do with general driver authors and I'm not sure
> what you mean here and where you are going with this.
Let me elaborate.
My general goal is that I want to make it easier (or as easy as
possible) for the general driver author to deploy runtime PM and
system-wide PM support - in an optimized manner. Therefore, I am
pondering over the solution you picked in this series, trying to
understand how it fits into those aspects.
Particular I am a bit worried from a complexity point of view, about
the part with skipping callbacks from the PM core. We have observed
some difficulties with the direct_complete path (i2c dw driver), which
is based on a similar approach as this one.
Additionally, in this case, to trigger skipping of callbacks to
happen, first, drivers needs to inform the middle-layer, second, the
middle layer acts on that information and then informs the PM core,
then in the third step, the PM core can decide what to do. It doesn't
sound straight-forward.
I guess I need to be convinced that this new approach is going to be
better than the the direct_complete path, so it somehow can replace it
along the road. Otherwise, we may end up just having yet another way
of skipping callbacks in the PM core and I don't like that.
Of course, I also realize this hole thing is opt-in, so nothing will
break and we are all good. :-)
>
>> That said, as the series don't include any changes for drivers making
>> use of the flag, could please fold in such change as it would provide
>> a more complete picture?
>
> I've already done so, see https://patchwork.kernel.org/patch/10007349/
>
> IMHO it's not really useful to drag this stuff (which doesn't change
> BTW) along with every iteration of the core patches.
Well, to me it's useful because it shows how these flags can/will be used.
Anyway, I thought you scraped that patch and was working on a new
version. I will have a look then.
[...]
>>> * device_resume_noirq - Execute a "noirq resume" callback for given device.
>>> * @dev: Device to handle.
>>> * @state: PM transition of the system being carried out.
>>> @@ -575,6 +587,12 @@ static int device_resume_noirq(struct de
>>> error = dpm_run_callback(callback, dev, state, info);
>>> dev->power.is_noirq_suspended = false;
>>>
>>> + if (dev_pm_may_skip_resume(dev)) {
>>> + pm_runtime_set_suspended(dev);
>>
>> According to the doc, the DPM_FLAG_LEAVE_SUSPENDED intends to leave
>> the device in runtime suspend state during system resume.
>> However, here you are actually trying to change its runtime PM state to that.
>
> So the doc needs to be fixed. :-)
Yep.
>
> But I'm guessing that this just is a misunderstanding and you mean the
> phrase "it may be desirable to leave some devices in runtime suspend
> after [...]". Yes, it is talking about "runtime suspend", but
> actually "runtime suspend" is the only kind of "suspend" you can leave
> a device in after a system transition to the working state. It never
> says that the device must have been suspended before the preceding
> system transition into a sleep state started.
My point is, it's isn't obvious why you need to make sure the device's
runtime PM status is set to "RPM_SUSPENDED" when leaving the resume
noirq phase. You did explain that somewhat above, thanks!
Perhaps you could fold in some of that information into the doc as well?
>
>> Moreover, you should check the return value from
>> pm_runtime_set_suspended().
>
> This is in "noirq", so failures of that are meaningless here.
>
>> Then I wonder, what should you do when it fails here?
>>
>> Perhaps a better idea is to do this in the noirq suspend phase,
>> because it allows you to bail out in case pm_runtime_set_suspended()
>> fails.
>
> This doesn't make sense, sorry.
What do you mean by "failures of that are meaningless here."?
I was suggesting, instead of calling pm_runtime_set_suspended() in the
noirq *resume* phase, why can't you do that in the noirq *suspend*
phase?
In the noirq *suspend* phase it's not too late to deal with errors!? Or is it?
[...]
Kind regards
Uffe
next prev parent reply other threads:[~2017-11-14 16:08 UTC|newest]
Thread overview: 135+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-16 1:12 [PATCH 0/12] PM / sleep: Driver flags for system suspend/resume Rafael J. Wysocki
2017-10-16 1:29 ` [PATCH 01/12] PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags Rafael J. Wysocki
2017-10-16 5:34 ` Lukas Wunner
2017-10-16 22:03 ` Rafael J. Wysocki
2017-10-16 6:28 ` Greg Kroah-Hartman
2017-10-16 22:05 ` Rafael J. Wysocki
2017-10-17 7:15 ` Greg Kroah-Hartman
2017-10-17 15:26 ` Rafael J. Wysocki
2017-10-18 6:56 ` Greg Kroah-Hartman
2017-10-16 6:31 ` Greg Kroah-Hartman
2017-10-16 22:07 ` Rafael J. Wysocki
2017-10-17 13:26 ` Greg Kroah-Hartman
2017-10-16 20:16 ` Alan Stern
2017-10-16 22:11 ` Rafael J. Wysocki
2017-10-18 23:17 ` [Update][PATCH v2 " Rafael J. Wysocki
2017-10-19 7:33 ` Greg Kroah-Hartman
2017-10-20 11:11 ` Rafael J. Wysocki
2017-10-20 11:35 ` Greg Kroah-Hartman
2017-10-20 11:28 ` Rafael J. Wysocki
2017-10-23 16:37 ` Ulf Hansson
2017-10-23 20:41 ` Rafael J. Wysocki
2017-10-16 1:29 ` [PATCH 02/12] PCI / PM: Use the NEVER_SKIP driver flag Rafael J. Wysocki
2017-10-23 16:40 ` Ulf Hansson
2017-10-16 1:29 ` [PATCH 03/12] PM: i2c-designware-platdrv: Use DPM_FLAG_SMART_PREPARE Rafael J. Wysocki
2017-10-23 16:57 ` Ulf Hansson
2017-10-16 1:29 ` [PATCH 04/12] PM / core: Add SMART_SUSPEND driver flag Rafael J. Wysocki
2017-10-23 19:01 ` Ulf Hansson
2017-10-24 5:22 ` Ulf Hansson
2017-10-24 8:55 ` Rafael J. Wysocki
2017-10-16 1:29 ` [PATCH 05/12] PCI / PM: Drop unnecessary invocations of pcibios_pm_ops callbacks Rafael J. Wysocki
2017-10-23 19:06 ` Ulf Hansson
2017-10-16 1:29 ` [PATCH 06/12] PCI / PM: Take SMART_SUSPEND driver flag into account Rafael J. Wysocki
2017-10-16 1:29 ` [PATCH 07/12] ACPI / LPSS: Consolidate runtime PM and system sleep handling Rafael J. Wysocki
2017-10-23 19:09 ` Ulf Hansson
2017-10-16 1:30 ` [PATCH 08/12] ACPI / PM: Take SMART_SUSPEND driver flag into account Rafael J. Wysocki
2017-10-16 1:30 ` [PATCH 09/12] PM / mfd: intel-lpss: Use DPM_FLAG_SMART_SUSPEND Rafael J. Wysocki
2017-10-31 15:09 ` Lee Jones
2017-10-31 16:28 ` Rafael J. Wysocki
2017-11-01 9:28 ` Lee Jones
2017-11-01 20:26 ` Rafael J. Wysocki
2017-11-08 11:08 ` Lee Jones
2017-10-16 1:30 ` [PATCH 10/12] PM / core: Add LEAVE_SUSPENDED driver flag Rafael J. Wysocki
2017-10-23 19:38 ` Ulf Hansson
2017-10-16 1:31 ` [PATCH 11/12] PM: i2c-designware-platdrv: Optimize power management Rafael J. Wysocki
2017-10-26 20:41 ` Wolfram Sang
2017-10-26 21:14 ` Rafael J. Wysocki
2017-10-16 1:32 ` [PATCH 12/12] PM / core: Add AVOID_RPM driver flag Rafael J. Wysocki
2017-10-17 15:33 ` Andy Shevchenko
2017-10-17 15:59 ` Rafael J. Wysocki
2017-10-17 16:25 ` Andy Shevchenko
2017-10-16 7:08 ` [PATCH 0/12] PM / sleep: Driver flags for system suspend/resume Greg Kroah-Hartman
2017-10-16 21:50 ` Rafael J. Wysocki
2017-10-17 8:36 ` Ulf Hansson
2017-10-17 15:25 ` Rafael J. Wysocki
2017-10-17 19:41 ` Ulf Hansson
2017-10-17 20:12 ` Alan Stern
2017-10-17 23:07 ` Rafael J. Wysocki
2017-10-18 0:39 ` Rafael J. Wysocki
2017-10-18 10:24 ` Rafael J. Wysocki
2017-10-18 12:34 ` Ulf Hansson
2017-10-18 21:54 ` Rafael J. Wysocki
2017-10-18 11:57 ` Ulf Hansson
2017-10-18 13:00 ` Rafael J. Wysocki
2017-10-18 14:11 ` Ulf Hansson
2017-10-18 19:45 ` Grygorii Strashko
2017-10-18 21:48 ` Rafael J. Wysocki
2017-10-19 8:33 ` Ulf Hansson
2017-10-19 17:21 ` Grygorii Strashko
2017-10-19 18:04 ` Ulf Hansson
2017-10-19 18:11 ` Ulf Hansson
2017-10-19 21:31 ` Grygorii Strashko
2017-10-20 6:05 ` Ulf Hansson
2017-10-18 22:12 ` Rafael J. Wysocki
2017-10-19 12:21 ` Ulf Hansson
2017-10-19 18:01 ` Ulf Hansson
2017-10-20 1:19 ` Rafael J. Wysocki
2017-10-20 5:57 ` Ulf Hansson
2017-10-20 20:46 ` Bjorn Helgaas
2017-10-21 1:04 ` Rafael J. Wysocki
2017-10-27 22:11 ` [PATCH v2 0/6] PM / sleep: Driver flags for system suspend/resume (part 1) Rafael J. Wysocki
2017-10-27 22:17 ` [PATCH v2 1/6] PM / core: Add NEVER_SKIP and SMART_PREPARE driver flags Rafael J. Wysocki
2017-11-06 8:07 ` Ulf Hansson
2017-10-27 22:19 ` [PATCH v2 2/6] PCI / PM: Use the NEVER_SKIP driver flag Rafael J. Wysocki
2017-10-27 22:22 ` [PATCH v2 3/6] PM / core: Add SMART_SUSPEND " Rafael J. Wysocki
2017-11-06 8:09 ` Ulf Hansson
2017-11-06 11:23 ` Rafael J. Wysocki
2017-10-27 22:23 ` [PATCH v2 4/6] PCI / PM: Drop unnecessary invocations of pcibios_pm_ops callbacks Rafael J. Wysocki
2017-10-27 22:27 ` [PATCH v2 5/6] PCI / PM: Take SMART_SUSPEND driver flag into account Rafael J. Wysocki
2017-10-31 22:48 ` Bjorn Helgaas
2017-10-27 22:30 ` [PATCH v2 6/6] ACPI " Rafael J. Wysocki
2017-11-08 0:41 ` [PATCH v2 0/6] PM / sleep: Driver flags for system suspend/resume (part 2) Rafael J. Wysocki
2017-11-08 13:25 ` [PATCH v2 1/6] PM / core: Add LEAVE_SUSPENDED driver flag Rafael J. Wysocki
2017-11-10 9:09 ` Ulf Hansson
2017-11-10 23:45 ` Rafael J. Wysocki
2017-11-11 0:41 ` Rafael J. Wysocki
2017-11-11 1:36 ` Rafael J. Wysocki
2017-11-14 16:07 ` Ulf Hansson [this message]
2017-11-15 1:48 ` Rafael J. Wysocki
2017-11-16 10:18 ` Ulf Hansson
2017-11-08 13:28 ` [PATCH v2 2/6] PCI / PM: Support for " Rafael J. Wysocki
2017-11-08 20:38 ` Bjorn Helgaas
2017-11-08 21:09 ` Rafael J. Wysocki
2017-11-08 13:34 ` [PATCH v2 3/6] ACPI / PM: Support for LEAVE_SUSPENDED driver flag in ACPI PM domain Rafael J. Wysocki
2017-11-08 13:37 ` [PATCH v2 4/6] PM / core: Add helpers for subsystem callback selection Rafael J. Wysocki
2017-11-08 13:38 ` [PATCH v2 5/6] PM / core: Direct handling of DPM_FLAG_LEAVE_SUSPENDED Rafael J. Wysocki
2017-11-08 13:39 ` [PATCH v2 6/6] PM / core: DPM_FLAG_SMART_SUSPEND optimization Rafael J. Wysocki
2017-11-12 0:34 ` [PATCH v3 0/6] PM / sleep: Driver flags for system suspend/resume (part 2) Rafael J. Wysocki
2017-11-12 0:37 ` [PATCH v3 1/6] PM / core: Add LEAVE_SUSPENDED driver flag Rafael J. Wysocki
2017-11-16 15:10 ` Ulf Hansson
2017-11-16 23:07 ` Rafael J. Wysocki
2017-11-17 6:11 ` Ulf Hansson
2017-11-17 13:18 ` Rafael J. Wysocki
2017-11-17 13:49 ` Ulf Hansson
2017-11-17 14:31 ` Rafael J. Wysocki
2017-11-17 15:57 ` Ulf Hansson
2017-11-17 12:45 ` Rafael J. Wysocki
2017-11-12 0:40 ` [PATCH v3 2/6] PCI / PM: Support for " Rafael J. Wysocki
2017-11-12 0:40 ` [PATCH v3 3/6] ACPI / PM: Support for LEAVE_SUSPENDED driver flag in ACPI PM domain Rafael J. Wysocki
2017-11-12 0:42 ` [PATCH v3 4/6] PM / core: Add helpers for subsystem callback selection Rafael J. Wysocki
2017-11-15 7:43 ` Ulf Hansson
2017-11-15 17:55 ` Rafael J. Wysocki
2017-11-12 0:43 ` [PATCH v3 5/6] PM / core: Direct handling of DPM_FLAG_LEAVE_SUSPENDED Rafael J. Wysocki
2017-11-12 0:44 ` [PATCH v3 6/6] PM / core: DPM_FLAG_SMART_SUSPEND optimization Rafael J. Wysocki
2017-11-18 14:27 ` [PATCH v4 0/6] PM / sleep: Driver flags for system suspend/resume (part 2) Rafael J. Wysocki
2017-11-18 14:31 ` [PATCH v4 1/6] PM / core: Add LEAVE_SUSPENDED driver flag Rafael J. Wysocki
2017-11-20 12:25 ` Ulf Hansson
2017-11-21 0:16 ` Rafael J. Wysocki
2017-11-18 14:33 ` [PATCH v4 2/6] PCI / PM: Support for " Rafael J. Wysocki
2017-11-18 14:35 ` [PATCH v4 3/6] ACPI / PM: Support for LEAVE_SUSPENDED driver flag in ACPI PM domain Rafael J. Wysocki
2017-11-18 14:37 ` [PATCH v4 4/6] PM / core: Add helpers for subsystem callback selection Rafael J. Wysocki
2017-11-18 14:41 ` [PATCH v4 5/6] PM / core: Direct handling of DPM_FLAG_LEAVE_SUSPENDED Rafael J. Wysocki
2017-11-20 13:42 ` Ulf Hansson
2017-11-22 1:10 ` Rafael J. Wysocki
2017-11-22 1:28 ` Rafael J. Wysocki
2017-11-18 14:44 ` [PATCH v4 6/6] PM / core: DPM_FLAG_SMART_SUSPEND optimization Rafael J. Wysocki
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