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Date:   Wed, 15 May 2019 15:02:56 +0200
From:   Niklas Cassel <niklas.cassel@linaro.org>
To:     Amit Kucheria <amit.kucheria@linaro.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Andy Gross <andy.gross@linaro.org>,
        David Brown <david.brown@linaro.org>,
        Li Yang <leoyang.li@nxp.com>, Shawn Guo <shawnguo@kernel.org>,
        DTML <devicetree@vger.kernel.org>
Subject: Re: [PATCHv1 4/8] arm64: dts: qcom: msm8916: Use more generic idle
 state names
Message-ID: <20190515130256.GA27174@centauri>
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On Wed, May 15, 2019 at 03:43:19PM +0530, Amit Kucheria wrote:
> On Tue, May 14, 2019 at 9:42 PM Niklas Cassel <niklas.cassel@linaro.org> wrote:
> >
> > On Fri, May 10, 2019 at 04:59:42PM +0530, Amit Kucheria wrote:
> > > Instead of using Qualcomm-specific terminology, use generic node names
> > > for the idle states that are easier to understand. Move the description
> > > into the "idle-state-name" property.
> > >
> > > Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
> > > ---
> > >  arch/arm64/boot/dts/qcom/msm8916.dtsi | 11 ++++++-----
> > >  1 file changed, 6 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/arch/arm64/boot/dts/qcom/msm8916.dtsi b/arch/arm64/boot/dts/qcom/msm8916.dtsi
> > > index ded1052e5693..400b609bb3fd 100644
> > > --- a/arch/arm64/boot/dts/qcom/msm8916.dtsi
> > > +++ b/arch/arm64/boot/dts/qcom/msm8916.dtsi
> > > @@ -110,7 +110,7 @@
> > >                       reg = <0x0>;
> > >                       next-level-cache = <&L2_0>;
> > >                       enable-method = "psci";
> > > -                     cpu-idle-states = <&CPU_SPC>;
> > > +                     cpu-idle-states = <&CPU_SLEEP_0>;
> > >                       clocks = <&apcs>;
> > >                       operating-points-v2 = <&cpu_opp_table>;
> > >                       #cooling-cells = <2>;
> > > @@ -122,7 +122,7 @@
> > >                       reg = <0x1>;
> > >                       next-level-cache = <&L2_0>;
> > >                       enable-method = "psci";
> > > -                     cpu-idle-states = <&CPU_SPC>;
> > > +                     cpu-idle-states = <&CPU_SLEEP_0>;
> > >                       clocks = <&apcs>;
> > >                       operating-points-v2 = <&cpu_opp_table>;
> > >                       #cooling-cells = <2>;
> > > @@ -134,7 +134,7 @@
> > >                       reg = <0x2>;
> > >                       next-level-cache = <&L2_0>;
> > >                       enable-method = "psci";
> > > -                     cpu-idle-states = <&CPU_SPC>;
> > > +                     cpu-idle-states = <&CPU_SLEEP_0>;
> > >                       clocks = <&apcs>;
> > >                       operating-points-v2 = <&cpu_opp_table>;
> > >                       #cooling-cells = <2>;
> > > @@ -146,7 +146,7 @@
> > >                       reg = <0x3>;
> > >                       next-level-cache = <&L2_0>;
> > >                       enable-method = "psci";
> > > -                     cpu-idle-states = <&CPU_SPC>;
> > > +                     cpu-idle-states = <&CPU_SLEEP_0>;
> > >                       clocks = <&apcs>;
> > >                       operating-points-v2 = <&cpu_opp_table>;
> > >                       #cooling-cells = <2>;
> > > @@ -160,8 +160,9 @@
> > >               idle-states {
> > >                       entry-method="psci";
> >
> > Please add a space before and after "=".
> >
> > >
> > > -                     CPU_SPC: spc {
> > > +                     CPU_SLEEP_0: cpu-sleep-0 {
> >
> > While I like your idea of using power state names from
> > Server Base System Architecture document (SBSA) where applicable,
> > does each qcom power state have a matching state in SBSA?
> >
> > These are the qcom power states:
> > https://source.codeaurora.org/quic/la/kernel/msm-4.4/tree/Documentation/devicetree/bindings/arm/msm/lpm-levels.txt?h=msm-4.4#n53
> >
> > Note that qcom defines:
> > "wfi", "retention", "gdhs", "pc", "fpc"
> > while SBSA simply defines "idle_standby" (aka wfi), "idle_retention", "sleep".
> >
> > Unless you know the equivalent name for each qcom power state
> > (perhaps several qcom power states are really the same SBSA state?),
> > I think that you should omit the renaming from this patch series.
> 
> That is what SLEEP_0, SLEEP_1, SLEEP_2 could be used for.

Ok, sounds good to me.

> 
> IOW, all these qcom definitions are nicely represented in the
> state-name and we could simply stick to SLEEP_0, SLEEP_1 for the node
> names. There is wide variability in the the names of the qcom idle
> states across SoC families downstream, so I'd argue against using
> those for the node names.
> 
> Just for cpu states (non-wfi) I see the use of the following names
> downstream across families. The C<num> seems to come from x86
> world[1]:
> 
>  - C4,   standalone power collapse (spc)
>  - C4,   power collapse (fpc)
>  - C2D, retention
>  - C3,   power collapse (pc)
>  - C4,   rail power collapse (rail-pc)
> 
> [1] https://www.hardwaresecrets.com/everything-you-need-to-know-about-the-cpu-c-states-power-saving-modes/

Indeed, there seems to be mixed names used, I've also seen "fpc-def".

So, you have convinced me.


Kind regards,
Niklas

> 
> > >                               compatible = "arm,idle-state";
> > > +                             idle-state-name = "standalone-power-collapse";
> > >                               arm,psci-suspend-param = <0x40000002>;
> > >                               entry-latency-us = <130>;
> > >                               exit-latency-us = <150>;
> > > --
> > > 2.17.1
> > >