linux-kernel - Re: [PATCH RESEND] CLK: ARC: Set initial pll output frequency specified in device tree

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Message-ID: <20171114234643.GD11955@codeaurora.org>
Date:   Tue, 14 Nov 2017 15:46:43 -0800
From:   "sboyd@...eaurora.org" <sboyd@...eaurora.org>
To:     Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Cc:     "vladimir_zapolskiy@...tor.com" <vladimir_zapolskiy@...tor.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH RESEND] CLK: ARC: Set initial pll output frequency
 specified in device tree

On 11/14, Alexey Brodkin wrote:
> Hi Vladimir,
> 
> On Tue, 2017-11-14 at 19:01 +0200, Vladimir Zapolskiy wrote:
> > On 11/14/2017 02:20 PM, Eugeniy Paltsev wrote:
> > > 
> > > Add option to set initial output frequency of plls via
> > > "clock-frequency" property in pll's device tree node.
> > > This frequency will be set while pll driver probed.
> > > 
> > > The usage example is setting CPU clock frequency on boot
> > > See discussion:
> > > https://urldefense.proofpoint.com/v2/url?u=https-3A__www.mail-2Darchive.com_linux-2Dsnps-2Darc-40lists.infradead.org_msg02689.html&d=DwICAg&c=DPL6
> > > _X_6JkXFx7AXWqB0tg&r=lqdeeSSEes0GFDDl656eViXO7breS55ytWkhpk5R81I&m=vTFoSv1E8NyQC8nqe6pwvuTDxGvEefhAdGwAoABOrY4&s=sbmMnczdKP317bN973cZn2WcYF29kVMLW
> > > chYfhSGT2M&e=
> > > 
> > > Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
> > > ---
> > >  .../bindings/clock/snps,hsdk-pll-clock.txt         |  5 ++++
> > >  .../devicetree/bindings/clock/snps,pll-clock.txt   |  5 ++++
> > >  drivers/clk/axs10x/pll_clock.c                     | 34 ++++++++++++++++++++--
> > >  drivers/clk/clk-hsdk-pll.c                         | 34 ++++++++++++++++++++--
> > >  4 files changed, 74 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/clock/snps,hsdk-pll-clock.txt b/Documentation/devicetree/bindings/clock/snps,hsdk-pll-clock.txt
> > > index c56c755..5703059 100644
> > > --- a/Documentation/devicetree/bindings/clock/snps,hsdk-pll-clock.txt
> > > +++ b/Documentation/devicetree/bindings/clock/snps,hsdk-pll-clock.txt
> > > @@ -13,6 +13,10 @@ Required properties:
> > >  - clocks: shall be the input parent clock phandle for the PLL.
> > >  - #clock-cells: from common clock binding; Should always be set to 0.
> > >  
> > > +Optional properties:
> > > +- clock-frequency: output frequency generated by pll in Hz which will be set
> > > +while probing. Should be a single cell.
> > > +
> > >  Example:
> > >  	input_clk: input-clk {
> > >  		clock-frequency = <33333333>;
> > > @@ -25,4 +29,5 @@ Example:
> > >  		reg = <0x00 0x10>;
> > >  		#clock-cells = <0>;
> > >  		clocks = <&input_clk>;
> > > +		clock-frequency = <1000000000>;
> > >  	};
> > > diff --git a/Documentation/devicetree/bindings/clock/snps,pll-clock.txt b/Documentation/devicetree/bindings/clock/snps,pll-clock.txt
> > > index 11fe487..5908f99 100644
> > > --- a/Documentation/devicetree/bindings/clock/snps,pll-clock.txt
> > > +++ b/Documentation/devicetree/bindings/clock/snps,pll-clock.txt
> > > @@ -13,6 +13,10 @@ registers and second for corresponding LOCK CGU register.
> > >  - clocks: shall be the input parent clock phandle for the PLL.
> > >  - #clock-cells: from common clock binding; Should always be set to 0.
> > >  
> > > +Optional properties:
> > > +- clock-frequency: output frequency generated by pll in Hz which will be set
> > > +while probing. Should be a single cell.
> > > +
> > >  Example:
> > >  	input-clk: input-clk {
> > >  		clock-frequency = <33333333>;
> > > @@ -25,4 +29,5 @@ Example:
> > >  		reg = <0x80 0x10>, <0x100 0x10>;
> > >  		#clock-cells = <0>;
> > >  		clocks = <&input-clk>;
> > > +		clock-frequency = <100000000>;
> > >  	};
> > 
> > You may check Documentation/devicetree/bindings/clock/clock-bindings.txt
> > about how to assign initial clock rates, in general 'clock-frequency'
> > property is a property of clock consumers with two exceptions of simple
> > clock sources, namely it is used in fixed clock and PWM clock bindings.
> 
> I think that's what we agreed on with Rob Herring back in the day.
> Have you checked this post of him on the topic?
> http://lists.infradead.org/pipermail/linux-snps-arc/2017-September/002909.html
> 
> Just FYI it all started from my question here:
> http://lists.infradead.org/pipermail/linux-snps-arc/2017-September/002900.html

Why can't we use assigned-clock-rates? That would basically call
clk_set_rate() on the clk once it's added.

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