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    SubjectRe: [RFC v2 4/9] of: add clock providers
    On Tue, Dec 13, 2011 at 11:01 AM, Rob Herring <robherring2@gmail.com> wrote:
    > Grant,
    >
    > On 12/13/2011 11:54 AM, Grant Likely wrote:
    >> On Mon, Dec 12, 2011 at 4:29 PM, Jamie Iles <jamie@jamieiles.com> wrote:
    >>> 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!
    >>
    >> I'm following convention here that has been established with
    >> interrupts, gpios, and others.  Sometimes more information is needed
    >> that just the clock number.  Using #clock-cells gives a clock provider
    >> the option of having additional fields for clock flags or other data.
    >> This is very much implementation defined.  Simple clock providers that
    >> only have a single clock output can easily use #clock-cells = <0>.
    >> Providers with multiple outputs will need to use 1 or more cells.
    >>
    >
    > Aren't you off by 1 here? The minimum cells is 1 to hold the phandle of
    > the source/parent. Multiple outputs will need a cell size of 2 (typically).

    No. The #clock-cells does not include the phandle. Never did.

    g.
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