@@ -30,6 +30,13 @@ properties:
minimum: 1
maximum: 5000000
+ i2c-parent:
+ $ref: /schemas/types.yaml#/definitions/phandle
+ description:
+ In case of an I2C bus extension, reference to the I2C bus controller
+ this extension is connected to. In other word, reference the I2C bus
+ controller on the fixed side that drives the bus extension.
+
i2c-scl-falling-time-ns:
description:
Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C
@@ -159,6 +166,25 @@ allOf:
- i2c-scl-has-clk-low-timeout
patternProperties:
+ 'i2c-bus-extension@[0-9a-f]+$':
+ type: object
+ description:
+ An I2C bus extension connected to an I2C bus. Those extensions allow to
+ decouple I2C busses when they are wired to connectors.
+
+ properties:
+ reg:
+ maxItems: 1
+
+ i2c-bus:
+ $ref: /schemas/types.yaml#/definitions/phandle
+ description:
+ Reference to the extension bus.
+
+ required:
+ - reg
+ - i2c-bus
+
'@[0-9a-f]+$':
type: object
@@ -221,3 +247,44 @@ dependentRequired:
i2c-digital-filter-width-ns: [ i2c-digital-filter ]
additionalProperties: true
+
+examples:
+ # I2C bus extension example involving an I2C bus controller and a connector.
+ #
+ # +--------------+ +-------------+ +-------------+
+ # | i2c@abcd0000 | | Connector | | Addon board |
+ # | (i2c1) +-----+ (i2c-addon) +-----+ (device@10) |
+ # | | | | | |
+ # +--------------+ +-------------+ +-------------+
+ #
+ # The i2c1 I2C bus is wired from a I2C controller to a connector. It is
+ # identified at connector level as i2c-addon bus.
+ # An addon board can be connected to this connector and connects a device
+ # (device@10) to this i2c-addon extension bus.
+ - |
+ i2c1: i2c@abcd0000 {
+ compatible = "xyz,i2c-ctrl";
+ reg = <0xabcd0000 0x100>;
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ i2c-bus-extension@0 {
+ reg = <0>;
+ i2c-bus = <&i2c_addon>;
+ };
+ };
+
+ connector {
+ i2c_addon: i2c-addon {
+ i2c-parent = <&i2c1>;
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ device@10 {
+ compatible = "xyz,foo";
+ reg = <0x10>;
+ };
+ };
+ };
+
+...
An I2C bus can be wired to the connector and allows an add-on board to connect additional I2C devices to this bus. Those additional I2C devices could be described as sub-nodes of the I2C bus controller node however for hotplug connectors described via device tree overlays there is additional level of indirection, which is needed to decouple the overlay and the base tree: --- base device tree --- i2c1: i2c@abcd0000 { compatible = "xyz,i2c-ctrl"; i2c-bus-extension@0 { i2c-bus = <&i2c_ctrl>; }; ... }; i2c5: i2c@cafe0000 { compatible = "xyz,i2c-ctrl"; i2c-bus-extension@0 { i2c-bus = <&i2c-sensors>; }; ... }; connector { i2c_ctrl: i2c-ctrl { i2c-parent = <&i2c1>; #address-cells = <1>; #size-cells = <0>; }; i2c-sensors { i2c-parent = <&i2c5>; #address-cells = <1>; #size-cells = <0>; }; }; --- device tree overlay --- ... // This node will overlay on the i2c-ctrl node of the base tree i2c-ctrl { eeprom@50 { compatible = "atmel,24c64"; ... }; }; ... --- resulting device tree --- i2c1: i2c@abcd0000 { compatible = "xyz,i2c-ctrl"; i2c-bus-extension@0 { i2c-bus = <&i2c_ctrl>; }; ... }; i2c5: i2c@cafe0000 { compatible = "xyz,i2c-ctrl"; i2c-bus-extension@0 { i2c-bus = <&i2c-sensors>; }; ... }; connector { i2c-ctrl { i2c-parent = <&i2c1>; #address-cells = <1>; #size-cells = <0>; eeprom@50 { compatible = "atmel,24c64"; ... }; }; i2c-sensors { i2c-parent = <&i2c5>; #address-cells = <1>; #size-cells = <0>; }; }; Here i2c-ctrl (same goes for i2c-sensors) represent the part of I2C bus that is on the hot-pluggable add-on. On hot-plugging it will physically connect to the I2C adapter on the base board. Let's call the 'i2c-ctrl' node an "extension node". In order to decouple the overlay from the base tree, the I2C adapter (i2c@abcd0000) and the extension node (i2c-ctrl) are separate nodes. The extension node is linked to the I2C bus controller in two ways. The first one with the i2c-bus-extension available in I2C controller sub-node and the second one with the i2c-parent property available in the extension node itself. The purpose of those two links is to provide the link in both direction from the I2C controller to the I2C extension and from the I2C extension to the I2C controller. Signed-off-by: Herve Codina <herve.codina@bootlin.com> Reviewed-by: Ayush Singh <ayush@beagleboard.org> --- dtschema/schemas/i2c/i2c-controller.yaml | 67 ++++++++++++++++++++++++ 1 file changed, 67 insertions(+)