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

[Stephen Warren <swarren@wwwdotorg.org>]

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>;
> +	};