linux-kernel - Re: [RFC/RFT][PATCH v2 3/7] PM / sleep: Make async suspend/resume of devices use device links

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Date:   Sun, 11 Sep 2016 00:12:30 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: Re: [RFC/RFT][PATCH v2 3/7] PM / sleep: Make async suspend/resume of
 devices use device links

On Sat, Sep 10, 2016 at 3:31 PM, Lukas Wunner <lukas@...ner.de> wrote:
> On Thu, Sep 08, 2016 at 11:28:33PM +0200, Rafael J. Wysocki wrote:
>> Make the device suspend/resume part of the core system
>> suspend/resume code use device links to ensure that supplier
>> and consumer devices will be suspended and resumed in the right
>> order in case of async suspend/resume.
>>
>> The idea, roughly, is to use dpm_wait() to wait for all consumers
>> before a supplier device suspend and to wait for all suppliers
>> before a consumer device resume.
>
> For devices with a parent/child relationship, if the child does not
> utilize direct_complete, the parent is not allowed to utilize it
> either and is runtime resumed upon system sleep.
>
> Don't we need the same for supplier/consumer relationships?
>
> The code enforcing this is in __device_suspend() and looks like this:
>
>         if (parent) {
>                 spin_lock_irq(&parent->power.lock);
>
>                 dev->parent->power.direct_complete = false;
>                 if (dev->power.wakeup_path
>                     && !dev->parent->power.ignore_children)
>                         dev->parent->power.wakeup_path = true;
>
>                 spin_unlock_irq(&parent->power.lock);
>         }
>
> I guess we need to iterate over the suppliers here and execute
> the block for each of them.

You are right about the direct_complete thing, but the wakeup_path
thing is another matter.  It is about forwarding wakeup signals up the
hierarchy and I'd confine it to parents at least for the time being.

Thanks,
Rafael