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

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Date:   Tue, 14 Nov 2017 19:01:28 +0200
From:   Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        <linux-clk@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-snps-arc@...ts.infradead.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH RESEND] CLK: ARC: Set initial pll output frequency
 specified in device tree

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://www.mail-archive.com/linux-snps-arc@lists.infradead.org/msg02689.html
> 
> 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.

--
With best wishes,
Vladimir