linux-kernel - Re: [PATCH v6 1/3] dt-bindings: opp: Introduce opp-peak-kBps and opp-avg-kBps bindings

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Date:   Wed, 8 Jan 2020 16:02:10 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Georgi Djakov <georgi.djakov@...aro.org>,
        vincent.guittot@...aro.org, seansw@....qualcomm.com,
        daidavid1@...eaurora.org, adharmap@...eaurora.org,
        Rajendra Nayak <rnayak@...eaurora.org>, sibis@...eaurora.org,
        bjorn.andersson@...aro.org, evgreen@...omium.org,
        kernel-team@...roid.com, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v6 1/3] dt-bindings: opp: Introduce opp-peak-kBps and
 opp-avg-kBps bindings

On 06-12-19, 16:24, Saravana Kannan wrote:
> Interconnects often quantify their performance points in terms of
> bandwidth. So, add opp-peak-kBps (required) and opp-avg-kBps (optional) to
> allow specifying Bandwidth OPP tables in DT.
> 
> opp-peak-kBps is a required property that replaces opp-hz for Bandwidth OPP
> tables.
> 
> opp-avg-kBps is an optional property that can be used in Bandwidth OPP
> tables.
> 
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> Reviewed-by: Rob Herring <robh@...nel.org>
> ---
>  Documentation/devicetree/bindings/opp/opp.txt     | 15 ++++++++++++---
>  .../devicetree/bindings/property-units.txt        |  4 ++++
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
> index 68592271461f..dbad8eb6c746 100644
> --- a/Documentation/devicetree/bindings/opp/opp.txt
> +++ b/Documentation/devicetree/bindings/opp/opp.txt
> @@ -83,9 +83,14 @@ properties.
>  
>  Required properties:
>  - opp-hz: Frequency in Hz, expressed as a 64-bit big-endian integer. This is a
> -  required property for all device nodes but devices like power domains. The
> -  power domain nodes must have another (implementation dependent) property which
> -  uniquely identifies the OPP nodes.
> +  required property for all device nodes except for devices like power domains
> +  or bandwidth opp tables.

Fine until here.

> The power domain nodes must have another
> +  (implementation dependent) property which uniquely identifies the OPP nodes.
> +  The interconnect opps are required to have the opp-peak-kBps property.

Maybe rewrite it as:

The devices which don't have this property must have another
(implementation dependent) property which uniquely identifies the OPP
nodes.

So we won't be required to update this again for another property.

> +
> +- opp-peak-kBps: Peak bandwidth in kilobytes per second, expressed as a 32-bit
> +  big-endian integer.

> This is a required property for all devices that don't
> +  have opp-hz.

This statement is surely incorrect, isn't it ? What about power-domain
tables ?

Suggest rewriting it as:

This is a required property for bandwidth OPP tables.

> For example, bandwidth OPP tables for interconnect paths.
>  
>  Optional properties:
>  - opp-microvolt: voltage in micro Volts.
> @@ -132,6 +137,10 @@ Optional properties:
>  - opp-level: A value representing the performance level of the device,
>    expressed as a 32-bit integer.
>  
> +- opp-avg-kBps: Average bandwidth in kilobytes per second, expressed as a
> +  32-bit big-endian integer. This property is only meaningful in OPP tables
> +  where opp-peak-kBps is present.
> +
>  - clock-latency-ns: Specifies the maximum possible transition latency (in
>    nanoseconds) for switching to this OPP from any other OPP.
>  
> diff --git a/Documentation/devicetree/bindings/property-units.txt b/Documentation/devicetree/bindings/property-units.txt
> index e9b8360b3288..c80a110c1e26 100644
> --- a/Documentation/devicetree/bindings/property-units.txt
> +++ b/Documentation/devicetree/bindings/property-units.txt
> @@ -41,3 +41,7 @@ Temperature
>  Pressure
>  ----------------------------------------
>  -kpascal	: kilopascal
> +
> +Throughput
> +----------------------------------------
> +-kBps		: kilobytes per second
> -- 
> 2.24.0.393.g34dc348eaf-goog

-- 
viresh