Messages in this thread | | | Date | Thu, 15 Dec 2011 21:51:30 +0800 | From | Shawn Guo <> | Subject | Re: [RFC v2 4/9] of: add clock providers |
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On Tue, Dec 13, 2011 at 10:54:58AM -0700, 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. > It totally destroys my understanding on #clock-cells :)
I thought it's introduced to reduce the clock nodes in dts. That said, #clock-cells stands for the number of clks we describe in the node. When #clock-cells > 1 for a node, the node becomes a clk blob which actually contains multiple clks. I migrated the imx6 clock to your first post with this approach [1], using 70 nodes to describe 110 clocks (~35% nodes reduced).
Now, you are saying it's not designed for this purpose. I'm pretty confused, because the only reasonable use of #clock-cells to me is just that way, and I fail to see why we need #clock-cells if we do not use it that way.
http://comments.gmane.org/gmane.linux.drivers.devicetree/9631
-- Regards, Shawn
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