linux-kernel - Re: [RFC PATCH] pm: prevent suspend until power supply events are processed

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Date:	Wed, 3 Sep 2014 10:35:35 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Anton Vorontsov <anton@...msg.org>, zrn.markovic@...il.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Arve Hjonnevag <arve@...roid.com>,
	Todd Poynor <toddpoynor@...gle.com>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [RFC PATCH] pm: prevent suspend until power supply events are processed

On Wed, Sep 3, 2014 at 10:09 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> Don't have Zoran's new email address, but probably other might have
> answers to my queries.

Got Zoran's email id finally :)

> I have just started with the power-supply framework a day or two back
> and so my understanding might not be good enough :)
>
> On Sat, Aug 3, 2013 at 2:08 AM, Zoran Markovic
> <zoran.markovic@...aro.org> wrote:
>> diff --git a/drivers/power/power_supply_core.c b/drivers/power/power_supply_core.c
>> index 3b2d5df..e68d598 100644
>> --- a/drivers/power/power_supply_core.c
>> +++ b/drivers/power/power_supply_core.c
>> @@ -67,23 +67,41 @@ static int __power_supply_changed_work(struct device *dev, void *data)
>>
>>  static void power_supply_changed_work(struct work_struct *work)
>>  {
>> +       unsigned long flags;
>>         struct power_supply *psy = container_of(work, struct power_supply,
>>                                                 changed_work);
>>
>>         dev_dbg(psy->dev, "%s\n", __func__);
>>
>> -       class_for_each_device(power_supply_class, NULL, psy,
>> -                             __power_supply_changed_work);
>> -
>> -       power_supply_update_leds(psy);
>> -
>> -       kobject_uevent(&psy->dev->kobj, KOBJ_CHANGE);
>> +       spin_lock_irqsave(&psy->changed_lock, flags);
>> +       if (psy->changed) {
>
> Can this be false here? We have reached here as the work was
> scheduled after setting it to true..
>
> Maybe a WARN_ON(psy->changed) is more sensible here ?
>
>> +               psy->changed = false;
>> +               spin_unlock_irqrestore(&psy->changed_lock, flags);
>> +               class_for_each_device(power_supply_class, NULL, psy,
>> +                                     __power_supply_changed_work);
>> +               power_supply_update_leds(psy);
>> +               kobject_uevent(&psy->dev->kobj, KOBJ_CHANGE);
>> +               spin_lock_irqsave(&psy->changed_lock, flags);
>> +       }
>> +       /* dependent power supplies (e.g. battery) may have changed
>> +        * state as a result of this event, so poll again and hold
>> +        * the wakeup_source until all events are processed.
>> +        */
>> +       if (!psy->changed)
>> +               pm_relax(psy->dev);
>
> I got a bit confused here. Does the above comment say this:
>
> The supplies dependent on 'psy' may change states and that *may*
> change the state of 'psy' again? And so psy->changed is set to true
> again?
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