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
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