Messages in this thread | | | Date | Tue, 13 Dec 2011 12:01:03 -0600 | From | Rob Herring <> | Subject | Re: [RFC v2 4/9] of: add clock providers |
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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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