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SubjectRe: [PATCH v1 0/3] Add required-opps support to devfreq passive gov
On Mon, Jun 24, 2019 at 2:43 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
>
> On 21-06-19, 17:34, Saravana Kannan wrote:
> > The devfreq passive governor scales the frequency of a "child" device
> > based on the current frequency of a "parent" device (not parent/child in
> > the sense of device hierarchy). As of today, the passive governor
> > requires one of the following to work correctly:
> > 1. The parent and child device have the same number of frequencies
> > 2. The child device driver passes a mapping function to translate from
> > parent frequency to child frequency.
> >
> > When (1) is not true, (2) is the only option right now. But often times,
> > all that is required is a simple mapping from parent's frequency to
> > child's frequency.
> >
> > Since OPPs already support pointing to other "required-opps", add
> > support for using that to map from parent device frequency to child
> > device frequency. That way, every child device driver doesn't have to
> > implement a separate mapping function anytime (1) isn't true.
>
> Can you please provide a real world example with DT code here so I
> can understand it better ?
>

Here's an example. This can't be done today, but can be done with this change.

In arch/arm64/boot/dts/exynos/exynos5433-bus.dtsi you have something
like this with the following changes:

bus_g2d_400: bus0 {
compatible = "samsung,exynos-bus";
clocks = <&cmu_top CLK_ACLK_G2D_400>;
clock-names = "bus";
operating-points-v2 = <&bus_g2d_400_opp_table>;
status = "disabled";
};

bus_noc2: bus9 {
compatible = "samsung,exynos-bus";
clocks = <&cmu_mif CLK_ACLK_BUS2_400>;
clock-names = "bus";
operating-points-v2 = <&bus_noc2_opp_table>;
status = "disabled";
};

bus_g2d_400_opp_table: opp_table2 {
compatible = "operating-points-v2";
opp-shared;

opp-400000000 {
opp-hz = /bits/ 64 <400000000>;
opp-microvolt = <1075000>;
+ required-opps = <&noc2_400>;
};
opp-267000000 {
opp-hz = /bits/ 64 <267000000>;
opp-microvolt = <1000000>;
+ required-opps = <&noc2_200>;
};
opp-200000000 {
opp-hz = /bits/ 64 <200000000>;
opp-microvolt = <975000>;
+ required-opps = <&noc2_200>;
};
opp-160000000 {
opp-hz = /bits/ 64 <160000000>;
opp-microvolt = <962500>;
+ required-opps = <&noc2_134>;
};
opp-134000000 {
opp-hz = /bits/ 64 <134000000>;
opp-microvolt = <950000>;
+ required-opps = <&noc2_134>;
};
opp-100000000 {
opp-hz = /bits/ 64 <100000000>;
opp-microvolt = <937500>;
+ required-opps = <&noc2_100>;
};
};

bus_noc2_opp_table: opp_table6 {
compatible = "operating-points-v2";

- opp-400000000 {
+ noc2_400: opp-400000000 {
opp-hz = /bits/ 64 <400000000>;
};
- opp-200000000 {
+ noc2_200: opp-200000000 {
opp-hz = /bits/ 64 <200000000>;
};
- opp-134000000 {
+ noc2_134: opp-134000000 {
opp-hz = /bits/ 64 <134000000>;
};
- opp-100000000 {
+ noc2_100: opp-100000000 {
opp-hz = /bits/ 64 <100000000>;
};
};

Thanks,
Saravana

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