linux-kernel - Re: [PATCH] arm64: dts: qcom: qcs404: Add PSCI cpuidle support

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Date:   Thu, 9 May 2019 23:19:23 +0530
From:   Amit Kucheria <amit.kucheria@...aro.org>
To:     Niklas Cassel <niklas.cassel@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>
Cc:     Andy Gross <agross@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>,
        Lina Iyer <lina.iyer@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: dts: qcom: qcs404: Add PSCI cpuidle support

(Adding Lorenzo and Sudeep)

On Wed, May 8, 2019 at 8:26 PM Niklas Cassel <niklas.cassel@...aro.org> wrote:
>
> On Wed, May 08, 2019 at 02:48:19AM +0530, Amit Kucheria wrote:
> > On Tue, May 7, 2019 at 1:01 AM Niklas Cassel <niklas.cassel@...aro.org> wrote:
> > >
> > > Add device bindings for CPUs to suspend using PSCI as the enable-method.
> > >
> > > Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
> > > ---
> > >  arch/arm64/boot/dts/qcom/qcs404.dtsi | 15 +++++++++++++++
> > >  1 file changed, 15 insertions(+)
> > >
> > > diff --git a/arch/arm64/boot/dts/qcom/qcs404.dtsi b/arch/arm64/boot/dts/qcom/qcs404.dtsi
> > > index ffedf9640af7..f9db9f3ee10c 100644
> > > --- a/arch/arm64/boot/dts/qcom/qcs404.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/qcs404.dtsi
> > > @@ -31,6 +31,7 @@
> > >                         reg = <0x100>;
> > >                         enable-method = "psci";
> > >                         next-level-cache = <&L2_0>;
> > > +                       cpu-idle-states = <&CPU_PC>;
> > >                 };
> > >
> > >                 CPU1: cpu@101 {
> > > @@ -39,6 +40,7 @@
> > >                         reg = <0x101>;
> > >                         enable-method = "psci";
> > >                         next-level-cache = <&L2_0>;
> > > +                       cpu-idle-states = <&CPU_PC>;
> > >                 };
> > >
> > >                 CPU2: cpu@102 {
> > > @@ -47,6 +49,7 @@
> > >                         reg = <0x102>;
> > >                         enable-method = "psci";
> > >                         next-level-cache = <&L2_0>;
> > > +                       cpu-idle-states = <&CPU_PC>;
> > >                 };
> > >
> > >                 CPU3: cpu@103 {
> > > @@ -55,12 +58,24 @@
> > >                         reg = <0x103>;
> > >                         enable-method = "psci";
> > >                         next-level-cache = <&L2_0>;
> > > +                       cpu-idle-states = <&CPU_PC>;
> > >                 };
> > >
> > >                 L2_0: l2-cache {
> > >                         compatible = "cache";
> > >                         cache-level = <2>;
> > >                 };
> > > +
> > > +               idle-states {
> >
> > entry-method="psci" property goes here. I have a patch fixing it for 410c ;-)
> >
> > I don't think the psci_cpuidle_ops will even get called without this.
>
> Hello Amit,
>
> I added debug prints in psci_cpu_suspend_enter() and arm_cpuidle_suspend()
> when verifying this patch, and psci_cpu_suspend_enter() is indeed called,
> with the correct psci suspend parameter.
>
> The output from:
> grep "" /sys/bus/cpu/devices/cpu0/cpuidle/state?/*
> also looks sane.
>
> However, if 'entry-method="psci"' is required according to the DT binding,
> perhaps you can send a 2/2 series that fixes both this patch and msm8916 ?

Last time I discussed this with Lorenzo and Sudeep (on IRC), I pointed
out that entry-method="psci" isn't checked for in code anywhere. Let's
get their view on this for posterity.

What does entry-method="psci" in the idle-states node achieve that
enable-method="psci" in the cpu node doesn't achieve? (Note: enable-
vs. entry-).

The enable-method property is the one that sets up the
psci_cpuidle_ops callbacks through the CPUIDLE_METHOD_OF_DECLARE
macro.

IOW, if we deprecated the entry-method property, everything would
still work, wouldn't it?
Do we expect to support PSCI platforms that might have a different
entry-method for idle states?
Should I whip up a patch removing entry-method? Since we don't check
for it today, it won't break the old DTs either.

Regards,
Amit


> > Did you see any changes in consumption with this patch? I was trying
> > to measure that before sending this out.
>
> I don't know of any way to measure the power consumption on this board,
> so no, I haven't been able to verify that the firmware actually does
> the right thing here.
>
>
> Kind regards,
> Niklas
>
> >
> > > +                       CPU_PC: pc {
> > > +                               compatible = "arm,idle-state";
> > > +                               arm,psci-suspend-param = <0x40000003>;
> > > +                               entry-latency-us = <125>;
> > > +                               exit-latency-us = <180>;
> > > +                               min-residency-us = <595>;
> > > +                               local-timer-stop;
> > > +                       };
> > > +               };
> > >         };
> > >
> > >         firmware {
> > > --
> > > 2.21.0
> > >