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

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Date:   Mon, 8 Jul 2019 08:43:31 +0000
From:   Anson Huang <anson.huang@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Leonard Crestez <leonard.crestez@....com>
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, Viresh

> On 04-07-19, 07:49, Leonard Crestez wrote:
> > 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?
> 
> What does this exactly mean ? How is the OPP made unavailable in your
> case ?

That is because in i.MX8M series SoCs, the speed grading and market segment
fuses settings could affect the OPP defined in DT, in a word, all possible OPPs
are defined in DT, but each parts could ONLY select some of them to be working
OPPs, so if the "opp-suspend" is added for 1 OPP in DT, if the part's speed grading or
market segment fuse settings make that OPP as unavailable,  then that "opp-suspend"
is NOT working at all.

> 
> What will dev_pm_opp_get_suspend_opp_freq() return in this case ?

If the OPP contains "opp-suspend" property is NOT supported by the HW, then there will
be no suspend OPP defined, so it will return 0. The _opp_is_supported() parses the opp-supported-hw
before opp-suspend.

> 
> > 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?

I ever tried that, go through the OPP table and check the fuse settings, then runtime add "opp-suspend"
to the opp table, but unfortunately, the " struct opp_table " is NOT opened to be used, it is a private
structure?

> 
> Sorry for jumping in late, the latest patch from Anson drew my attention to
> this topic :)

That is OK😊

Thanks,
Anson.