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    SubjectRe: [RFC v2 4/9] of: add clock providers
    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).

    Rob


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