Messages in this thread | | | From | Grant Likely <> | Date | Thu, 15 Dec 2011 10:37:19 -0700 | Subject | Re: [RFC v2 4/9] of: add clock providers |
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On Thu, Dec 15, 2011 at 8:13 AM, Shawn Guo <shawn.guo@freescale.com> wrote: > On Thu, Dec 15, 2011 at 08:23:17AM -0600, Rob Herring wrote: >> >> >> On 12/15/2011 07:51 AM, Shawn Guo wrote: >> > 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 >> >> Think of clock-cells as the size of array elements (minus 1), not the >> number of array elements. If you have more than 1 clock per node, then >> you need more information on the clock input side than just a phandle to >> describe which clock you are using. Typically this would just be the >> phandle plus index of the clock you want. This is just like gpio where >> you have controller phandle plus gpio line number. >> > It seems I misunderstood/misused the #clock-cells. So even we have > multiple clks embedded in a node, #clock-cells=1 works for most of the > cases, since what really matters is just the index of the clk we want > the phandle to point to. And the clock driver has to figure out how > many clks are in there by some other means. Correct me please, if I > still misunderstand it.
Yes, it sounds like you have it right.
g.
-- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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