Hi Stephen,

Am Mittwoch, 31. Juli 2013, 15:03:14 schrieb Stephen Warren:

The generic I2C bindings already define that the other chips on the I2C
bus appear directly underneath the I2C controller's DT node. Perhaps it
isn't a big issue to change that, since each I2C controller can define
the layout of its own node?

Anyway, we can probably get away without introducing multiple levels by
adding some more bits or cells into the reg address for I2C child nodes:

i2c@xxxxxxxx {
	compatible = "nvidia,tegra20-i2c";
	... resources
	#address-cells = <2>;

	codec {
		// 0 means external slave, 0x1c is slave's address
		reg = <0 0x1c>;
		...
	};

	tegraslave {
		// 0 means internal slave, 0x80 is controller's address
		reg = <1 0x80>;
		...
	};
};

... where each of those child nodes could be repeated N times. We could
also or in 0x80000000 to the reg values in the child nodes rather than
using a separate cell if we wanted.

thinking a little more about this, this is way to complicated. "Master" and 
"Slave" functions are properties of the same i2c controller. Therefore, just 
adding a small property to the i2c controller node saying "enable slave 
support" is sufficient, as all the resources are shared (which is another good 
argument that it is the same device, hence same node). I would just add the 
slave i2c address, which is all the slave driver needs, e.g.
"slave-address = <8c>;" to enable slave mode operation. Both modes can be 
enabled at the same time (for loopback comm). AFAIK, if only the slave part is 
used, the master part shouldn't hurt if programmed (same as other way around).

The difficult part is how to specify the master if only the slave is used. As 
the master is naturally on the same bus as the slave, it should be a child 
node of the controller. Therefore it needs a special i2c address, maybe 
0x80000000 as you mentioned above, but this will be rejected by the i2c core. 
Instantiating the nvec as an i2c client could be another problem.

It looks like that the i2c subsystem needs some modifications to allow to 
specify a master device which is attached to a slave controller. Maybe someone 
from the i2c folks (cc'ed) can comment on this?

Marc