linux-kernel - Re: [PATCH 1/3] dt-bindings: power: Introduce 'assigned-performance-states' property

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Date:   Fri, 8 Jan 2021 10:39:15 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Roja Rani Yarubandi <rojay@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Matthias Kaehlcke <mka@...omium.org>, akashast@...eaurora.org,
        msavaliy@....qualcomm.com, parashar@...eaurora.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Andy Gross <agross@...nel.org>, linux-i2c@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: power: Introduce 'assigned-performance-states'
 property

On Thu, 31 Dec 2020 at 16:49, Rob Herring <robh@...nel.org> wrote:
>
> On Thu, Dec 24, 2020 at 04:42:08PM +0530, Roja Rani Yarubandi wrote:
> > While most devices within power-domains which support performance states,
> > scale the performance state dynamically, some devices might want to
> > set a static/default performance state while the device is active.
> > These devices typically would also run off a fixed clock and not support
> > dynamically scaling the device's performance, also known as DVFS
> > techniques.
> >
> > Add a property 'assigned-performance-states' which client devices can
> > use to set this default performance state on their power-domains.
> >
> > Signed-off-by: Roja Rani Yarubandi <rojay@...eaurora.org>
> > ---
> >  .../bindings/power/power-domain.yaml          | 49 +++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/power/power-domain.yaml b/Documentation/devicetree/bindings/power/power-domain.yaml
> > index aed51e9dcb11..a42977a82d06 100644
> > --- a/Documentation/devicetree/bindings/power/power-domain.yaml
> > +++ b/Documentation/devicetree/bindings/power/power-domain.yaml
> > @@ -66,6 +66,18 @@ properties:
> >        by the given provider should be subdomains of the domain specified
> >        by this binding.
> >
> > +  assigned-performance-states:
> > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > +    description:
> > +       Some devices might need to configure their power domains in a default
> > +       performance state while the device is active. These devices typcially
> > +       would also run off a fixed clock and not support dynamically scaling
> > +       the device's performance, also known as DVFS techniques. Each cell in
> > +       performance state value corresponds to one power domain specified as
> > +       part of the power-domains property. Performance state value can be an
> > +       opp-level inside an OPP table of the power-domain and need not match
> > +       with any OPP table performance state.
>
> Couldn't this just be an additional cell in 'power-domains'?

Right. Some SoCs already use the cell to specify per device SoC
specific data [1].

Although, I am wondering if we shouldn't consider
"assigned-performance-states" as a more generic binding. I think it
would be somewhat comparable with the existing "assigned-clock-rates"
binding, don't you think?

[...]

Kind regards
Uffe

[1]
Documentation/devicetree/bindings/soc/ti/sci-pm-domain.txt