linux-kernel - RE: Re: Re: devfreq relation with pm qos

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Message-ID: <20180712023444epcms1p8cb202bb977fcb2b365bc334f87244d04@epcms1p8>
Date:   Thu, 12 Jul 2018 11:34:44 +0900
From:   MyungJoo Ham <myungjoo.ham@...sung.com>
To:     noman pouigt <variksla@...il.com>
CC:     "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: Re: Re: devfreq relation with pm qos

>MyungJo, I am trying to understand the relationship of PM QOS with
>devfreq drivers. I don't see any relation of PM QOS api's with devfreq drivers
>directly as there are no QOS apis used in the devfreq framework.
>
>The only explanation I have is that PM QOS has direct relationship
>with CPUFREQ driver and as CPUFREQ driver works with CPU
>frequency and that CPU frequency directly affects DEVFREQ drivers
>as devfreq driver maps CPU frequency to device frequency and
>that is why PM QOS doesn’t have direct relation with PM QOS.
>
>Is my understanding right?

Your understanding on the fact that there is no relation between
PM QOS and Devfreq framework of today's code is correct.

The reason on why so is not.
In general, you don't make a peripheral device be directly throttled
by CPUFreq values. There exist such cases, but they are not
"general" or inherit characteristics of peripheral devices.

Cheers,
MyungJoo.