linux-kernel - Re: [RFC PATCH 6/9] dt-bindings: opp: Add qcom-opp bindings with properties needed for CPR

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Date:   Tue, 9 Apr 2019 14:53:52 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-msm@...r.kernel.org, jorge.ramirez-ortiz@...aro.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 6/9] dt-bindings: opp: Add qcom-opp bindings with
 properties needed for CPR

On 04-04-19, 07:09, Niklas Cassel wrote:
> Add qcom-opp bindings with properties needed for Core Power Reduction (CPR).
> 
> CPR is included in a great variety of Qualcomm SoC, e.g. msm8916 and msm8996,
> and was first introduced in msm8974.
> 
> Co-developed-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
> Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@...aro.org>
> Signed-off-by: Niklas Cassel <niklas.cassel@...aro.org>
> ---
>  .../devicetree/bindings/opp/qcom-opp.txt      | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/opp/qcom-opp.txt
> 
> diff --git a/Documentation/devicetree/bindings/opp/qcom-opp.txt b/Documentation/devicetree/bindings/opp/qcom-opp.txt
> new file mode 100644
> index 000000000000..d24280467db7
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/opp/qcom-opp.txt
> @@ -0,0 +1,24 @@
> +Qualcomm OPP bindings to describe OPP nodes
> +
> +The bindings are based on top of the operating-points-v2 bindings
> +described in Documentation/devicetree/bindings/opp/opp.txt
> +Additional properties are described below.
> +
> +* OPP Table Node
> +
> +Required properties:
> +- compatible: Allow OPPs to express their compatibility. It should be:
> +  "operating-points-v2-qcom-level"
> +
> +* OPP Node
> +
> +Optional properties:
> +- opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer. Even
> +  though a power domain doesn't need a opp-hz, there can be devices in the
> +  power domain that need to know the highest supported frequency for each
> +  corner/level (e.g. CPR), in order to properly initialize the hardware.
> +
> +- qcom,opp-fuse-level: A positive value representing the fuse corner/level
> +  associated with this OPP node. Sometimes several corners/levels shares
> +  a certain fuse corner/level. A fuse corner/level contains e.g. ref uV,
> +  min uV, and max uV.

I know we discussed this sometime back and so you implemented it this way.

Looking at the implementation of the CPR driver, I now wonder if that was a good
choice. Technically a single domain can manage many devices, a big and a little
CPU for example and then we will have different highest frequencies for both of
them. How will we configure the CPR hardware in such a case ? Isn't the
programming per-device ?

-- 
viresh