linux-kernel - RE: [PATCH 2/2] arm64: dts: imx8mm: Assign highest opp as suspend opp

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Date:   Thu, 4 Jul 2019 08:00:24 +0000
From:   Anson Huang <anson.huang@....com>
To:     Leonard Crestez <leonard.crestez@....com>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        Jacky Bai <ping.bai@....com>,
        Daniel Baluta <daniel.baluta@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        Abel Vesa <abel.vesa@....com>,
        "andrew.smirnov@...il.com" <andrew.smirnov@...il.com>,
        "ccaione@...libre.com" <ccaione@...libre.com>,
        "angus@...ea.ca" <angus@...ea.ca>,
        "agx@...xcpu.org" <agx@...xcpu.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH 2/2] arm64: dts: imx8mm: Assign highest opp as suspend opp

Hi, Leonard

> On 7/4/2019 9:23 AM, Anson.Huang@....com wrote:
> > From: Anson Huang <Anson.Huang@....com>
> >
> > Assign highest OPP as suspend OPP to reduce suspend/resume latency on
> > i.MX8MM.
> >
> > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > ---
> >   arch/arm64/boot/dts/freescale/imx8mm.dtsi | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > index b11fc5e..3a62407 100644
> > --- a/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > +++ b/arch/arm64/boot/dts/freescale/imx8mm.dtsi
> > @@ -136,6 +136,7 @@
> >   			opp-microvolt = <1000000>;
> >   			opp-supported-hw = <0x8>, <0x3>;
> >   			clock-latency-ns = <150000>;
> > +			opp-suspend;
> >   		};
> >   	};
> 
> What if the highest OPP is unavailable due to speed grading? Ideally we
> should find a way to suspend at the highest *supported* OPP.
> 
> Maybe the opp-suspend marking could be assigned from imx-cpufreq-dt
> driver code?

Yes, this is also my concern, the current OPP driver does NOT handle it well, and
I was thinking to assigne it from imx-cpufreq-dt driver, 1 option is to runtime add
"suspend-opp" property into DT OPP node after parsing the speed grading fuse and
OPP table, but I do NOT like that very much, as we need to manually create a property,
the other option is to change cpu freq policy inside imx-cpufreq-dt driver in suspend/resume
callback? Which one do you prefer?

Thanks,
Anson

> 
> --
> Regards,
> Leonard