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.
Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/
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