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

[Rob Herring <robh@kernel.org>]

On Fri, Mar 23, 2018 at 12:00:14PM +0100, Boris Brezillon wrote:
> From: Boris Brezillon <boris.brezillon@free-electrons.com>
> 
> 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.

Mostly looks fine, a couple of clarifications below.

> 
> Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> ---
> Changes in v3:
> - Rename {i2c,i3c}-scl-frequency DT prop into {i2c,i3c}-scl-hz
> - Rework the way we expose the provisional ID and LVR information
> - Rename dynamic-address into assigned-address
> - Enforce the I3C master node name
> 
> Changes in v2:
> - Define how to describe I3C devices in the DT and when it should be
>   used. Note that the parsing of I3C devices is not yet implemented in
>   the framework. Will be added when someone really needs it.
> ---
>  Documentation/devicetree/bindings/i3c/i3c.txt | 140 ++++++++++++++++++++++++++
>  1 file changed, 140 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..ed858228d26b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/i3c/i3c.txt
> @@ -0,0 +1,140 @@
> +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 <3>. Read more about addresses below.
> +- #size-cells     - should be <0>.
> +- compatible      - name of the I3C master controller driving the I3C bus
> +
> +For other required properties e.g. to describe register sets,
> +clocks, etc. check the binding documentation of the specific driver.
> +The node describing an I3C bus should be named i3c-master.
> +
> +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-hz: frequency of the SCL signal used for I3C transfers.
> +	      When undefined the core sets it to 12.5MHz.
> +
> +- i2c-scl-hz: frequency of the SCL signal used for I2C transfers.
> +	      When undefined, the core looks at LVR (Legacy Virtual Register)
> +	      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. All
> +properties described in Documentation/devicetree/bindings/i2c/i2c.txt are
> +valid here, but several new properties have been added.
> +
> +New constraint on existing properties:
> +--------------------------------------
> +- reg: contains 3 cells
> +  + first cell : still encoding the I2C address
> +
> +  + second cell: should have bit 31 set to 1 signify that this is an I2C
> +		 device. Bits 0 to 7 encode the I3C LVR (Legacy Virtual
> +		 Register):
> +
> +	bit[7:5]: I2C device index. Possible values
> +	* 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 (Fast Mode) or FM+ mode
> +	* 0: FM+ mode
> +	* 1: FM mode
> +
> +	bit[3:0]: device type
> +	* 0-15: reserved
> +
> +  + third cell: should be 0
> +
> +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.

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

s/static-address/static-i2c-address/

> +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?

> +
> +  + 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.
> +
> +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
> 
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