linux-kernel - Re: [PATCH v4 1/4] dt-bindings/opp: Update documentation for opp-shared

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Date:   Tue, 8 Dec 2020 09:59:24 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Nicola Mazzucato <nicola.mazzucato@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v4 1/4] dt-bindings/opp: Update documentation for
 opp-shared

Subject should rather be:

dt-bindings: opp: Allow empty OPP tables

On 02-12-20, 17:23, Nicola Mazzucato wrote:
> Currently the optional property opp-shared is used within an opp table
> to tell that a set of devices share their clock/voltage lines (and the
> opp points).
> It is therefore possible to use an empty opp table to convey only that
> information, useful in situations where the opp points are provided via
> other means (hardware. firmware, etc).
> 
> Update the documentation to remark this additional case and provide an
> example.
> 
> Signed-off-by: Nicola Mazzucato <nicola.mazzucato@....com>
> ---
>  Documentation/devicetree/bindings/opp/opp.txt | 53 +++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
> index 9847dfeeffcb..a5f1f993eab9 100644
> --- a/Documentation/devicetree/bindings/opp/opp.txt
> +++ b/Documentation/devicetree/bindings/opp/opp.txt
> @@ -72,6 +72,9 @@ Optional properties:
>    switch their DVFS state together, i.e. they share clock/voltage/current lines.
>    Missing property means devices have independent clock/voltage/current lines,
>    but they share OPP tables.
> +  This optional property can be used without any OPP nodes when its only purpose
> +  is to describe a dependency of clock/voltage/current lines among a set of
> +  devices.

And instead of this, we should rather update "OPP nodes:" section like
this:

diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
index 9847dfeeffcb..28077ce3a845 100644
--- a/Documentation/devicetree/bindings/opp/opp.txt
+++ b/Documentation/devicetree/bindings/opp/opp.txt
@@ -63,11 +63,13 @@ This describes the OPPs belonging to a device. This node can have following
 - compatible: Allow OPPs to express their compatibility. It should be:
   "operating-points-v2".
 
+Optional properties:
 - OPP nodes: One or more OPP nodes describing voltage-current-frequency
   combinations. Their name isn't significant but their phandle can be used to
-  reference an OPP.
+  reference an OPP. These are mandatory except for the case where the OPP table
+  is present only to indicate dependency between devices using the opp-shared
+  property.
 
-Optional properties:
 - opp-shared: Indicates that device nodes using this OPP Table Node's phandle
   switch their DVFS state together, i.e. they share clock/voltage/current lines.
   Missing property means devices have independent clock/voltage/current lines,

-- 
viresh