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

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Message-ID: <CAJZ5v0j+_JSynHx8ajqJ0FqCf8ZijwpU=xTnPtEGiR9Tik9srQ@mail.gmail.com>
Date:   Sat, 4 Nov 2017 12:58:27 +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 12:30 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> 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.

Actually, no.  The value is ignored if action is PM_QOS_REMOVE_REQ, so
it is better to simply check the action under the WARN_ON() too.

Thanks,
Rafael