On Tue, Mar 05, 2013 at 07:52:21AM +0100, Guennadi Liakhovetski wrote:
> Hi Simon
>
> On Tue, 5 Mar 2013, Simon Horman wrote:
>
> > On Mon, Mar 04, 2013 at 02:33:40PM +0100, Guennadi Liakhovetski wrote:
>
> [snip]
>
> > > That would be the best, I agree. However, we discussed this already on the
> > > example of mmcif, you might remember. I asked what's the difference
> > > between extending a DT node (from .dtsi) with additional properties (in a
> > > board-specific .dts) using an "&phandle" syntax and a full path? Or are
> > > they equivalent? There was no reply, so, for such nodes (MMC/SD) I so far
> > > settled with complete nodes in .dts. We do use the "&phandle" syntax for
> > > pinctrl function groups, for I2C devices. I used a complete path for
> > > CPUFreq... Mostly because other platforms did that too.
> >
> > I am confused.
> >
> > Using phandle syntax we can add a device to an soc's dtsi file and then add
> > extra properties in the board file. This seems to be match the HW well.
> >
> > What is your alternate suggestion?
>
> Let me give you examples. In sh73a0-reference.dtsi we define an I2C device
> #0:
>
> i2c0: i2c@0xe6820000 {
> #address-cells = <1>;
> #size-cells = <0>;
> compatible = "renesas,rmobile-iic";
> reg = <0xe6820000 0x425>;
> ...
> };
>
> Then in sh73a0-kzm9g-reference.dts I can use the phandle syntax to put
> devices on that I2C bus:
>
> &i2c0 {
> as3711@40 {
> compatible = "ams,as3711";
> reg = <0x40>;
> ...
> };
> ...
> };
>
> This is one possibility. In sh73a0.dtsi we've got
>
> cpus {
> #address-cells = <1>;
> #size-cells = <0>;
>
> cpu@0 {
> device_type = "cpu";
> compatible = "arm,cortex-a9";
> reg = <0>;
> };
> ...
> };
>
> Now, I can also extend this in sh73a0-kzm9g-reference.dts to add CPUFreq
> support to CPU0:
>
> cpus {
> cpu@0 {
> cpu0-supply = <&vdd_dvfs>;
> operating-points = <
> /* kHz uV */
> 1196000 1315000
> 598000 1175000
> 398667 1065000
> >;
> voltage-tolerance = <1>; /* 1% */
> };
> };
>
> Which AFAICS does a similar thing (adds more properties to an existing DT
> node) but uses a different syntax. Maybe they are completely equivalent,
> the only difference being, that the former example uses a phandle and the
> latter a complete path, maybe there are differences, I don't know.
Interesting. Thanks for the example, I now understand.
To be honest I'm not sure what the answer is.
But if they are both working then I'm not particularly fussed either way.
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