Re: [PATCH v3 05/11] dt-bindings: i3c: Document core bindings

Boris Brezillon
2018-03-28T08:19:22Z

Hi Rob,

On Mon, 26 Mar 2018 17:24:58 -0500
Rob Herring <robh@kernel.org> wrote:

> > +
> > +I3C devices
> > +===========
> > +
> > +All I3C devices are supposed to support DAA (Dynamic Address Assignment), and
> > +are thus discoverable. So, by default, I3C devices do not have to be described
> > +in the device tree.
> > +This being said, one might want to attach extra resources to these devices,
> > +and those resources may have to be described in the device tree, which in turn
> > +means we have to describe I3C devices.
> > +
> > +Another use case for describing an I3C device in the device tree is when this
> > +I3C device has a static address and we want to assign it a specific dynamic
> > +address before the DAA takes place (so that other devices on the bus can't
>
> static is I2C address and dynamic is an I3C address. That could be
> clearer throughout.

I'll clarify that.

>
> > +take this dynamic address).
> > +
> > +The I3C device should be names <device-type>@<static-address>,<i3c-pid>,
>
> s/static-address/static-i2c-address/

Okay.

>
> > +where device-type is describing the type of device connected on the bus
> > +(gpio-controller, sensor, ...).
> > +
> > +Required properties
> > +-------------------
> > +- reg: contains 3 cells
> > + + first cell : encodes the I2C address. Should be 0 if the device does not
> > + have one (0 is not a valid I3C address).
>
> Change here to "encodes the static I2C address".
>
> 0 is not a valid I2C address?

According to [1] it is reserved, and it's reserved in the I3C spec
anyway (see "Table 9 I3C Slave Address Restrictions" in the I3C spec).

>
> > +
> > + + second and third cells: should encode the ProvisionalID. The second cell
> > + contains the manufacturer ID left-shifted by 1.
> > + The third cell contains ORing of the part ID
> > + left-shifted by 16, the instance ID left-shifted
> > + by 12 and the extra information. This encoding is
> > + following the PID definition provided by the I3C
> > + specification.

One extra question for you: should I refer to the I3C_DEV(),
I3C_DEV_WITH_STATIC_ADDR() and I2C_DEV() macros in the bindings doc?
And if I do, should I use them my example?

Thanks,

Boris

> > +
> > +Optional properties
> > +-------------------
> > +- assigned-address: dynamic address to be assigned to this device. This
> > + property is only valid if the I3C device has a static
> > + address (first cell of the reg property != 0).
> > +
> > +
> > +Example:
> > +
> > + i3c-master@d040000 {
> > + compatible = "cdns,i3c-master";
> > + clocks = <&coreclock>, <&i3csysclock>;
> > + clock-names = "pclk", "sysclk";
> > + interrupts = <3 0>;
> > + reg = <0x0d040000 0x1000>;
> > + #address-cells = <3>;
> > + #size-cells = <0>;
> > +
> > + status = "okay";
> > + i2c-scl-frequency = <100000>;
> > +
> > + /* I2C device. */
> > + nunchuk: nunchuk@52 {
> > + compatible = "nintendo,nunchuk";
> > + reg = <0x52 0x80000010 0x0>;
> > + };
> > +
> > + /* I3C device with a static address. */
> > + thermal_sensor: sensor@68,39200144004 {
> > + reg = <0x68 0x392 0x144004>;
> > + assigned-address = <0xa>;
> > + };
> > +
> > + /*
> > + * I3C device without a static address but requiring resources
> > + * described in the DT.
> > + */
> > + sensor@0,39200154004 {
> > + reg = <0x0 0x392 0x154004>;
> > + clocks = <&clock_provider 0>;
> > + };
> > + };
> > +
> > --
> > 2.14.1
> >

[1]http://www.i2c-bus.org/addressing

--
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering