linux-kernel - Re: [PATCH] clk: si570: Add a driver for SI570 oscillators

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Date:	Mon, 16 Sep 2013 10:34:28 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Rob Landley <rob@...dley.net>,
	Mike Turquette <mturquette@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Guenter Roeck <linux@...ck-us.net>, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Hyun Kwon <hyunk@...inx.com>
Subject: Re: [PATCH] clk: si570: Add a driver for SI570 oscillators

On 09/12/2013 06:55 PM, Soren Brinkmann wrote:
> Add a driver for SILabs 570, 571, 598, 599 programmable oscillators.
> The devices generate low-jitter clock signals and are reprogrammable via
> an I2C interface.

> diff --git a/Documentation/devicetree/bindings/clock/silabs,si570.txt b/Documentation/devicetree/bindings/clock/silabs,si570.txt

> +Required properties:
> + - compatible: Shall be one of "silabs,si57x", "silabs,si59x".
> + - reg: I2C device address.
> + - #clock-cells: From common clock bindings: Shall be 0.
> + - factory-fout: Factory set default frequency

So, there's no way to query this from the device at all? Looking at the
data-sheet, all the frequency generation parameters are in registers,
and the device supports I2C read commands. As such, I'm not convinced
this property is necessary.

> +Optional properties:
> + - initial-fout: Initial output frequency to set during probe

"probe" is a Linux-specific concept. This property should be removed. If
the driver is asked to set a specific frequency, it should do so, but I
don't think it should program something pro-actively just because it
starts up.

If this property is acceptable, it'd be better to describe it more along
the lines of the following:

initial-fout: The frequency at which the system requires the clock to
operate.

> + - temperature-stability-7ppm: Indicate a device with a temperature stability
> +			       of 7ppm
> +
> +Example:
> +	si570: clock-generator@5d {
> +		#clock-cells = <0>;
> +		compatible = "silabs,si570";
> +		reg = <0x5d>;
> +		factory-fout = <156250000>;
> +	};

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