linux-kernel - Re: [v4, 7/8] cpufreq: mediatek: add opp notification for SVS support

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Message-ID: <20191018095300.mtygp2ej7rnz6uzn@vireshk-i7>
Date:   Fri, 18 Oct 2019 15:23:00 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "andrew-sh.cheng" <andrew-sh.cheng@...iatek.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Nishanth Menon <nm@...com>, Stephen Boyd <sboyd@...nel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Fan Chen (陳凡) <fan.chen@...iatek.com>
Subject: Re: [v4, 7/8] cpufreq: mediatek: add opp notification for SVS support

On 18-10-19, 17:03, andrew-sh.cheng wrote:
> On Thu, 2019-10-17 at 12:01 +0530, Viresh Kumar wrote:
> > On 16-10-19, 10:43, andrew-sh.cheng wrote:
> > > This is due to SVS feature need to fix Vproc for calibration.
> > > When SVS calibration, it want to disable all opp items, except one with
> > > voltae 1.0V. (SVS will change the voltage field of that opp item, if the
> > > corresponding voltage is not 1.0V)
> > > In this way, SVS can make sure there is no other module, include
> > > thermal, will change Vproc by DVFS driver.
> > > After SVS calibration done, SVS will enable those disabled opp items
> > > back.
> > 
> > But why is this required to be done this way ? Why can't we just update the
> > voltages without doing this disable/enable dance ?
> > 
> This is because some opp items need voltage larger than 1.0V.
> We cannot update the voltage to 1.0V.
> 
> If we don't disable these opp items, and DVFS policy want to set these
> high frequencies, dvfs driver will set higher voltage to Vproc and SVS
> calibration will be fail.

Okay.

-- 
viresh