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Date: Mon, 12 Dec 2011 23:29:03 +0000
From: Jamie Iles <jamie@...ieiles.com>
To: Grant Likely <grant.likely@...retlab.ca>
Cc: linux-kernel@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
Rob Herring <rob.herring@...xeda.com>,
Sascha Hauer <kernel@...gutronix.de>,
Mike Turquette <mturquette@...com>
Subject: Re: [RFC v2 4/9] of: add clock providers
Hi Grant,
I'm still going through these and trying to digest them but a couple of
quick questions/comments.
Jamie
On Mon, Dec 12, 2011 at 03:02:04PM -0700, Grant Likely wrote:
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> new file mode 100644
> index 0000000..e40c436
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> @@ -0,0 +1,114 @@
> +This binding is a work-in-progress, and are based on some experimental
> +work by benh[1].
> +
> +Sources of clock signal can be represented by any node in the device
> +tree. Those nodes are designated as clock providers. Clock consumer
> +nodes use a phandle and clock specifier pair to connect clock provider
> +outputs to clock inputs. Similar to the gpio specifiers, a clock
> +specifier is an array of one more more cells identifying the clock
> +output on a device. The length of a clock specifier is defined by the
> +value of a #clock-cells property in the clock provider node.
> +
> +[1] http://patchwork.ozlabs.org/patch/31551/
> +
> +==Clock providers==
> +
> +Required properties:
> +#clock-cells: Number of cells in a clock specifier; typically will be
> + set to 1
I'm not sure I fully understand what the extra cells actually mean for
clocks. I think the first integer is the clock output to use but some
of the versatile and highbank ones only have a phandle or is it more
implementation defined? The clock-output-names description hints at
recommended, so I find this a little confusing, but that could just be
me!
> +Optional properties:
> +clock-output-names: Recommended to be a list of strings of clock output signal
> + names indexed by the first cell in the clock specifier.
> + However, the meaning of clock-output-name is domain
> + specific to the clock provider, and is only provided to
> + encourage using the same meaning for the majority of clock
> + providers. This format may not work for clock providers
> + using a complex clock specifier format. In those cases it
> + is recommended to omit this property and create a binding
> + specific names property.
> +
> + Clock consumer nodes must never directly reference
> + the provider's clock-output-name property.
> +
> +For example:
> +
> + oscillator {
> + #clock-cells = <1>;
> + clock-output-names = "ckil", "ckih";
> + };
> +
> +- this node defines a device with two clock outputs, the first named
> + "ckil" and the second named "ckih". Consumer nodes always reference
> + clocks by index. The names should reflect the clock output signal
> + names for the device.
> +
> +==Clock consumers==
> +
> +Required properties:
> +clocks: List of phandle and clock specifier pairs, one pair
> + for each clock input to the device.
Some of the highbank and versatile devicetree nodes have clocks
properties that aren't a pair e.g. versatile timer has
"clocks = <&tim_clk>;".
> +clock-names: List of clock input name strings sorted in the same
> + order as the clocks property. Consumers drivers
> + will use clock-names to match clock input names
> + with clocks specifiers.
The versatile and highbank patches appears to omit this required
property in several nodes. So is this really optional?
Jamie
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