linux-kernel - Re: [PATCH/RFC V6 2/2] clk: Add handling of clk parent and rate assigned from DT

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Date:	Thu, 22 May 2014 18:35:46 -0700
From:	Mike Turquette <mturquette@...aro.org>
To:	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org
Cc:	linux@....linux.org.uk, robh+dt@...nel.org,
	grant.likely@...aro.org, mark.rutland@....com,
	galak@...eaurora.org, pawel.moll@....com,
	kyungmin.park@...sung.com, sw0312.kim@...sung.com,
	m.szyprowski@...sung.com, t.figa@...sung.com,
	linux-kernel@...r.kernel.org,
	"Sylwester Nawrocki" <s.nawrocki@...sung.com>
Subject: Re: [PATCH/RFC V6 2/2] clk: Add handling of clk parent and rate assigned
 from DT

Quoting Sylwester Nawrocki (2014-05-19 10:22:51)
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> index 700e7aa..bee649b 100644
> --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> @@ -132,3 +132,35 @@ clock signal, and a UART.
>    ("pll" and "pll-switched").
>  * The UART has its baud clock connected the external oscillator and its
>    register clock connected to the PLL clock (the "pll-switched" signal)
> +
> +==Assigned clock parents and rates==
> +
> +Some platforms require static initial configuration of default parent clocks
> +and clock frequecies. Such a configuration can be specified in a device node

s/frequecies/frequencies/

> +through clock-parents and clock-rates DT properties. The former should contain
> +a list of parent clocks in form of phandle and clock specifier pairs, the
> +latter the list of assigned clock frequency values (one cell each).
> +To skip setting parent or rate of a clock its corresponding entry should be
> +set to 0, or can be omitted if it is not followed by any non-zero entry.
> +
> +    uart@...0 {
> +        compatible = "fsl,imx-uart";
> +        reg = <0xa000 0x1000>;
> +        ...
> +        clocks = <&clkcon 0>, <&clkcon 3>;
> +        clock-names = "baud", "mux";
> +
> +        clock-parents = <0>, <&pll 1>;
> +        clock-rates = <460800>;
> +    };
> +
> +In this example the pll is set as parent of "mux" clock and frequency of
> +"baud" clock is specified as 460800 Hz.
> +
> +Configuring a clock's parent and rate through the device node that consumes
> +the clock can be done only for clocks that have a single user. Specifying
> +conflicting parent or rate configuration in multiple consumer nodes for
> +a shared clock is forbidden.
> +
> +Configuration of common clocks, which affect multiple consumer devices can
> +be similarly specified in the clock provider node.

Is it worthwhile to show an example of this? I guess the outcome will
depend on whether or not we support "assigned-clocks" property, which I
just revisited in the V5 thread.

Regards,
Mike
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