linux-kernel - Re: [PATCH RFC v4 2/2] clk: Add handling of clk parent and rate assigned from DT

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Date:	Tue, 01 Apr 2014 11:31:57 +0200
From:	Sylwester Nawrocki <s.nawrocki@...sung.com>
To:	Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	gregkh@...uxfoundation.org, mturquette@...aro.org,
	linux@....linux.org.uk, robh+dt@...nel.org,
	grant.likely@...aro.org, mark.rutland@....com,
	galak@...eaurora.org, kyungmin.park@...sung.com,
	sw0312.kim@...sung.com, m.szyprowski@...sung.com,
	t.figa@...sung.com, laurent.pinchart@...asonboard.com
Subject: Re: [PATCH RFC v4 2/2] clk: Add handling of clk parent and rate
 assigned from DT

On 01/04/14 08:23, Sascha Hauer wrote:
>> tree/bindings/clock/clock-bindings.txt
>> > b/Documentation/devicetree/bindings/clock/clock-bindings.txt
>>> > >index 700e7aa..59fbb4e 100644
>>> > >--- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
>>> > >+++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
>>> > >@@ -132,3 +132,45 @@ 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 parts of the clocks
>>> > >+controller. Such a configuration can be specified in a clock consumer node
>>> > >+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).
>>> > >+
>>> > >+    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.
[...]
>> > 
>> > How do you support not-setting a rate for a clock?
>
> Not setting a rate is supported by specifying the rate to 0. That should
> be documented of course.

Yes, a rate won't be set for a clock if its corresponding entry in
clock-rates property is set to 0. Sorry, should have mentioned it.

Would adding a sentence as below to end of the first paragraph above
make it clear ?

"To skip setting a rate or parent for a clock the value of a corresponding
entry in the clock-rates or clock-parents property respectively should
be set to 0. The trailing zeros can be omitted."

--
Thanks,
Sylwester
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