linux-kernel - Re: [RFC] Migrate to Hz resolution for OPP binding

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Date:	Thu, 22 May 2014 08:27:39 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [RFC] Migrate to Hz resolution for OPP binding

On Tue, May 20, 2014 at 5:30 PM, Sören Brinkmann
<soren.brinkmann@...inx.com> wrote:
> Hi,
>
> I guess this is just to evaluate how big the lynch mob will be. Anyway:
> Triggered by this discussion https://lkml.org/lkml/2014/5/15/46, I
> looked a little into what it would take to migrate everybody to Hz
> frequency resolutions to avoid all the conversions between cpufreq, CCF,
> OPPs, etc.
> Turns out, OPPs are already stored in Hz resolution in the kernel, but the DT
> bindings use kHz resolution to specify them in DT. So, code-wise there
> is just a removal of a multiplication in the OPP parser (see below), but
> then there are the DT bindings...

Add this to the list of issues with the current OPP binding and define
a new binding, not a band-aid.

> As plan B, I was thinking to add the property 'operating-points-hz'...
>
> Any better ideas?

Fix clk_round_rate to specify how you want to round. There are
usecases for both rounding up and down. Don't you have the same
rounding problem with hz? Assume the person filling in OPP values
knows nothing about the kernel and you could have values rounded both
ways.

Rob
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