linux-kernel - Re: [v4, 6/8] PM / OPP: Support adjusting OPP voltages at runtime

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Message-ID: <1572595738.6939.7.camel@mtksdaap41>
Date:   Fri, 1 Nov 2019 16:08:58 +0800
From:   Roger Lu <roger.lu@...iatek.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
CC:     Andrew-sh Cheng (鄭式勳) 
        <andrew-sh.cheng@...iatek.com>,
        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>, Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [v4, 6/8] PM / OPP: Support adjusting OPP voltages at runtime

Dear Viresh,

Sorry for the late reply.

On Mon, 2019-08-19 at 19:18 +0800, Viresh Kumar wrote:
> On 13-08-19, 21:31, Andrew-sh.Cheng wrote:
> > From: Stephen Boyd <sboyd@...eaurora.org>
> > 
> > On some SoCs the Adaptive Voltage Scaling (AVS) technique is
> > employed to optimize the operating voltage of a device. At a
> > given frequency, the hardware monitors dynamic factors and either
> > makes a suggestion for how much to adjust a voltage for the
> > current frequency, or it automatically adjusts the voltage
> > without software intervention. Add an API to the OPP library for
> > the former case, so that AVS type devices can update the voltages
> > for an OPP when the hardware determines the voltage should
> > change. The assumption is that drivers like CPUfreq or devfreq
> > will register for the OPP notifiers and adjust the voltage
> > according to suggestions that AVS makes.
> > 
> > This patch is devired from [1] submitted by Stephen.
> > [1] https://lore.kernel.org/patchwork/patch/599279/
> > 
> > Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> > Signed-off-by: Roger Lu <roger.lu@...iatek.com>
> > ---
> >  drivers/opp/core.c     | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/linux/pm_opp.h | 11 +++++++++
> >  2 files changed, 74 insertions(+)
> > 
> > diff --git a/drivers/opp/core.c b/drivers/opp/core.c
> > index c094d5d20fd7..407a07f29b12 100644
> > --- a/drivers/opp/core.c
> > +++ b/drivers/opp/core.c
> > @@ -2054,6 +2054,69 @@ static int _opp_set_availability(struct device *dev, unsigned long freq,
> >  }
> >  
> >  /**
> > + * dev_pm_opp_adjust_voltage() - helper to change the voltage of an OPP
> > + * @dev:		device for which we do this operation
> > + * @freq:		OPP frequency to adjust voltage of
> > + * @u_volt:		new OPP voltage
> > + *
> > + * Return: -EINVAL for bad pointers, -ENOMEM if no memory available for the
> > + * copy operation, returns 0 if no modifcation was done OR modification was
> > + * successful.
> > + */
> > +int dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
> > +			      unsigned long u_volt)
> 
> Can you please update this to take a triplet instead ? That is what we are
> storing in OPP core now a days.

I've studied opp/core.c and still don't know meaning of triplet here.
Could you give me more hints (reference API?) about how to take a
triplet instead? Thanks in advance.