linux-kernel - Re: [PATCH V8 3/3] OPP: Allow "opp-hz" and "opp-microvolt" to contain magic values

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Date:   Tue, 26 Dec 2017 14:29:55 -0600
From:   Rob Herring <robh@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     ulf.hansson@...aro.org, Kevin Hilman <khilman@...nel.org>,
        Viresh Kumar <vireshk@...nel.org>, Nishanth Menon <nm@...com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        rnayak@...eaurora.org, sudeep.holla@....com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V8 3/3] OPP: Allow "opp-hz" and "opp-microvolt" to
 contain magic values

On Mon, Dec 18, 2017 at 03:51:30PM +0530, Viresh Kumar wrote:
> On some platforms the exact frequency or voltage may be hidden from the
> OS by the firmware. Allow such configurations to pass magic values in
> the "opp-hz" or the "opp-microvolt" properties, which should be
> interpreted in a platform dependent way.
> 
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
>  Documentation/devicetree/bindings/opp/opp.txt | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/opp/opp.txt b/Documentation/devicetree/bindings/opp/opp.txt
> index 4e4f30288c8b..00a3bdbd0f1f 100644
> --- a/Documentation/devicetree/bindings/opp/opp.txt
> +++ b/Documentation/devicetree/bindings/opp/opp.txt
> @@ -167,6 +167,12 @@ properties.
>    functioning of the current device at the current OPP (where this property is
>    present).
>  
> +
> +On some platforms the exact frequency or voltage may be hidden from the OS by
> +the firmware and the "opp-hz" or the "opp-microvolt" properties may contain
> +magic values that represent the frequency or voltage in a firmware dependent
> +way, for example an index of an array in the firmware.

I'm still not convinced this is a good idea. If you have firmware 
partially managing things, then I think we should have platform specific 
bindings or drivers. 

This is complex enough I'm not taking silence from Stephen as an okay.

Rob