linux-kernel - Re: [RFT][PATCH v2 2/2] PM / QoS: Fix device resume latency framework

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Date:   Sat, 4 Nov 2017 12:30:10 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Ramesh Thomas <ramesh.thomas@...el.com>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Tero Kristo <t-kristo@...com>, Alex Shi <alex.shi@...aro.org>
Subject: Re: [RFT][PATCH v2 2/2] PM / QoS: Fix device resume latency framework

On Sat, Nov 4, 2017 at 3:28 AM, Ramesh Thomas <ramesh.thomas@...el.com> wrote:
> On 2017-11-03 at 09:39:08 -0700, Reinette Chatre wrote:
>> Hi Rafael,
>>
>> I started to test this but found myself triggering one of the warnings:
>>
>> On 11/3/2017 4:50 AM, Rafael J. Wysocki wrote:
>> > --- linux-pm.orig/include/linux/pm_qos.h
>> > +++ linux-pm/include/linux/pm_qos.h
>> > @@ -28,16 +28,19 @@ enum pm_qos_flags_status {
>> >     PM_QOS_FLAGS_ALL,
>> >  };
>> >
>> > -#define PM_QOS_DEFAULT_VALUE -1
>> > +#define PM_QOS_DEFAULT_VALUE       (-1)
>>
>> PM_QOS_DEFAULT_VALUE is -1 ...
>>
>>
>> > ===================================================================
>> > --- linux-pm.orig/drivers/base/power/qos.c
>> > +++ linux-pm/drivers/base/power/qos.c
>> > @@ -139,6 +139,9 @@ static int apply_constraint(struct dev_p
>> >
>> >     switch(req->type) {
>> >     case DEV_PM_QOS_RESUME_LATENCY:
>> > +           if (WARN_ON(value < 0))
>> > +                   value = 0;
>> > +
>>
>> ... causing me to hit this WARN_ON because apply_constraint() is called by __dev_pm_qos_remove_request() with the value parameter set to PM_QOS_DEFAULT_VALUE.
>
> That value does not get used if action is PM_QOS_REMOVE_REQ. May be just pass
> 0 or PM_QOS_RESUME_LATENCY_DEFAULT_VALUE everywhere apply_constraint is called
> with PM_QOS_REMOVE_REQ action.

I think it's better to pass the "no constraint" value as that should
not reorder it to the top of the list.

Thanks,
Rafael