Q: define i2c nodes in device tree?

Hi all,

I have some probably dumb questions regarding the definition of i2c slaves in the of device tree file...

My test system is a lite5200b board to which I attached two pca8575 io expander chips at i2c addresses 0x20 and 0x21. Using the stock kernel 2.6.29, I added the driver from the GPIO section, but I couldn't figure out how to add them to the dts file. I tried e.g.

<snip>

i2c@3d40 {
	[...]
        compatible = "fsl,mpc5200b-i2c","fsl,mpc5200-i2c","fsl-i2c";
        [...]

        gpio@20 {
                compatible = "pcf857x";
                device_type = "gpio";
                reg = <0x20 1>;
	};
};

</snip>

and some other like "gpio-controller" instead of "gpio" but (surprise) it doesn't work - dmesg says that the driver is registered, but nothing else shows up. Unfortunately, I couldn't find documentation about the naming conventions of the i2c child nodes.

As I actually want to use the chips as parallel io (not separate gpio's) and thus would need to write my own driver I wonder if I really have to declare it in the device tree? Would the simple way -just load the kernel module as with arm/intel- also work? Would it be possible to use additional resources like an interrupt pin on the '5200 without the device tree?

Any information about a proper approach would be really helpful!

Thanks in advance, Albrecht.

2009/3/26 Albrecht Dre=DF <[email protected]>:

g

You need to have a "gpio I2C" device driver that registers the same name as what's in the DTS, like this:

cs4270:codec@4f {
	compatible =3D "cirrus,cs4270";
	reg =3D <0x4f>;
	/* MCLK source is a stand-alone oscillator */
	clock-frequency =3D <12288000>;
};

...

static struct i2c_device_id cs4270_id[] =3D {
	{"cs4270", 0},
	{}
};

MODULE_DEVICE_TABLE(i2c, cs4270_id);

and

re

le as

urces

No, the only acceptable way to do this is on PowerPC is with a device tree entry and a driver that registers itself properly.

--=20
Timur Tabi
Linux kernel developer at Freescale