On Mon, Jul 31, 2017 at 06:24:48PM +0200, Boris Brezillon wrote:
> A new I3C subsystem has been added and a generic description has been
> created to represent the I3C bus and the devices connected on it.
> 
> Document this generic representation.
> 
> Signed-off-by: Boris Brezillon <boris.brezil...@free-electrons.com>
> ---
>  Documentation/devicetree/bindings/i3c/i3c.txt | 90 
> +++++++++++++++++++++++++++
>  1 file changed, 90 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/i3c/i3c.txt
> 
> diff --git a/Documentation/devicetree/bindings/i3c/i3c.txt 
> b/Documentation/devicetree/bindings/i3c/i3c.txt
> new file mode 100644
> index 000000000000..49261dec7b01
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i3c/i3c.txt
> @@ -0,0 +1,90 @@
> +Generic device tree bindings for I3C busses
> +===========================================
> +
> +This document describes generic bindings that should be used to describe I3C
> +busses in a device tree.
> +
> +Required properties
> +-------------------
> +
> +- #address-cells  - should be <1>. Read more about addresses below.
> +- #size-cells     - should be <0>.
> +- compatible      - name of I3C bus controller following generic names
> +                 recommended practice.
> +
> +For other required properties e.g. to describe register sets,
> +clocks, etc. check the binding documentation of the specific driver.
> +
> +Optional properties
> +-------------------
> +
> +These properties may not be supported by all I3C master drivers. Each I3C
> +master bindings should specify which of them are supported.
> +
> +- i3c-scl-frequency: frequency (in Hz) of the SCL signal used for I3C
> +                  transfers. When undefined the core set it to 12.5MHz.
> +
> +- i2c-scl-frequency: frequency (in Hz) of the SCL signal used for I2C
> +                  transfers. When undefined, the core looks at LVR values
> +                  of I2C devices described in the device tree to determine
> +                  the maximum I2C frequency.
> +
> +I2C devices
> +===========
> +
> +Each I2C device connected to the bus should be described in a subnode with
> +the following properties:
> +
> +All properties described in Documentation/devicetree/bindings/i2c/i2c.txt are
> +valid here.
> +
> +New required properties:
> +------------------------
> +- i3c-lvr: 32 bits integer property (only the lowest 8 bits are meaningful)

What does lvr mean?

> +        describing device capabilities as described in the I3C
> +        specification.
> +
> +        bit[31:8]: unused
> +        bit[7:5]: I2C device index. Possible values

index? Seems more like flags

> +         * 0: I2C device has a 50 ns spike filter
> +         * 1: I2C device does not have a 50 ns spike filter but supports high
> +              frequency on SCL
> +         * 2: I2C device does not have a 50 ns spike filter and is not
> +              tolerant to high frequencies
> +         * 3-7: reserved
> +
> +        bit[4]: tell whether the device operates in FM or FM+ mode
> +         * 0: FM+ mode
> +         * 1: FM mode
> +
> +        bit[3:0]: device type
> +         * 0-15: reserved

That's useful...

> +
> +I3C devices
> +===========
> +
> +I3C are not described in the device tree yet. We could decide to represent 
> them
> +at some point to assign a specific dynamic address to a device or to force an
> +I3C device to act as an I2C device if it has a static address.

I think we need to define this sooner rather than later if there's not a 
standard connector. That's the only thing that would enforce any sort of 
standard. Of course, that didn't help with SDIO.

> +
> +Example:
> +
> +     i3c-master@0d040000 {

The node name should go into the DT spec. I tend to think "i3c" would be 
sufficient and aligned with i2c.

> +             compatible = "cdns,i3c-master";
> +             clocks = <&coreclock>, <&i3csysclock>;
> +             clock-names = "pclk", "sysclk";
> +             interrupts = <3 0>;
> +             reg = <0x0d040000 0x1000>;
> +             #address-cells = <1>;
> +             #size-cells = <0>;
> +
> +             status = "okay";
> +             i2c-scl-frequency = <100000>;
> +
> +             nunchuk: nunchuk@52 {
> +                     compatible = "nintendo,nunchuk";
> +                     reg = <0x52>;
> +                     i3c-lvr = <0x10>;
> +             };
> +     };
> +
> -- 
> 2.7.4
> 

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