linux-kernel - Re: [PATCH v2 0/3] renesas: irqchip: Use WAKEUP

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Date:   Sun, 31 Dec 2017 12:47:58 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Simon Horman <horms@...ge.net.au>,
        Niklas Soderlund <niklas.soderlund+renesas@...natech.se>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        linux-gpio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/3] renesas: irqchip: Use WAKEUP_PATH driver PM flag

On Sun, Dec 31, 2017 at 10:22 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> Hi Rafael,
>
> On Sun, Dec 31, 2017 at 1:56 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
>> On Fri, Dec 29, 2017 at 2:31 PM, Ulf Hansson <ulf.hansson@...aro.org> wrote:
>>> From: Geert Uytterhoeven <geert+renesas@...der.be>
>>>
>>> Changes in v2: [By Ulf Hansson]
>>>         - I have picked up the series from Geert [1] and converted it into use
>>>         the WAKEUP_PATH driver PM flag. This includes some minor changes to each
>>>         patch and updates to the changelogs.
>>>         - An important note, the WAKEUP_PATH driver PM flag is introduced in a
>>>         separate series [2], not yet applied, so @subject series depends on it.
>>>         - One more note, two of the patches has a checkpatch error, however I
>>>         did not fix them, becuase I think that should be done separate.
>>>
>>> [1]
>>> https://lkml.org/lkml/2017/11/9/382
>>> [2]
>>> https://marc.info/?l=linux-pm&m=151454744124661&w=2
>>>
>>> More information below, picked from Geert's previous cover letter.
>>>
>>> Kind regards
>>> Uffe
>>>
>>>
>>> Hi all,
>>>
>>> If an interrupt controller in a Renesas ARM SoC is part of a Clock
>>> Domain, and it is part of the wakeup path, it must be kept active during
>>> system suspend.
>>>
>>> Currently this is handled in all interrupt controller drivers by
>>> explicitly increasing the use count of the module clock when the device
>>> is part of the wakeup path.  However, this explicit clock handling is
>>> merely a workaround for a failure to properly communicate wakeup
>>> information to the device core.
>>>
>>> Hence this series fixes the affected drivers by setting the devices'
>>> power.wakeup_path fields instead, to indicate they are part of the
>>> wakeup path.  Depending on the PM Domain's active_wakeup configuration,
>>> the genpd core code will keep the device enabled (and the clock running)
>>> during system suspend when needed.
>>
>> However, there is a convention, documented in the kerneldoc comment of
>> device_init_wakeup(), by which devices participating in system wakeup
>> "passively" (like USB controllers and hubs) are expected to have it
>> enabled by default.
>>
>> If that convention was followed by the devices in question here, the
>> wakeup_path bit would be set for them and no other code changes would
>> be necessary.  So is there any reason for not following it?
>
> Yes there is.  The need to stay enabled during system suspend depends
> on the consumer of the interrupt. It is controlled by the consumer using
> the irq_chip.irq_set_wake() callback at runtime, and may change at runtime.
>
> If the wakeup_path flag is always set, the interrupt controller will
> never be suspended during system suspend, and thus waste power.

OK

For IRQ chips in particular, I think, you don't need add new fields to
struct dev_pm_info to make it work.

In ->suspend (or ->suspend_late, which may be better) you can check
the IRQD_WAKEUP_STATE flag of the irq_desc associated with the pin.
If that is set, you can simply set power.wakeup_path for the device
and that will make genpd skip it.  Wouldn't that work?

Thanks,
Rafael