From: Wolfram Sang <wsa+rene...@sang-engineering.com>
These bindings allow an I2C bus to switch between multiple masters. This
is not hot-swichting because connected I2C slaves will be
re-instantiated. It is meant to select the best I2C core at runtime once
the task is known. Example: Prefer i2c-gpio over another I2C core
because of HW errata affetcing your use case.
Signed-off-by: Wolfram Sang <wsa+rene...@sang-engineering.com>
---
.../devicetree/bindings/i2c/i2c-demux-pinctrl.txt | 155 +++++++++++++++++++++
1 file changed, 155 insertions(+)
create mode 100644 Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt
diff --git a/Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt
b/Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt
new file mode 100644
index 00000000000000..de571be68f4754
--- /dev/null
+++ b/Documentation/devicetree/bindings/i2c/i2c-demux-pinctrl.txt
@@ -0,0 +1,155 @@
+Pinctrl-based I2C Bus DeMux
+
+This binding describes an I2C bus demultiplexer that uses pin multiplexing to
+route the I2C signals, and represents the pin multiplexing configuration using
+the pinctrl device tree bindings. This may be used to select one I2C IP core at
+runtime which may have a better feature set for a given task than another I2C
+IP core on the SoC. The most simple example is to fall back to GPIO bitbanging
+if your current runtime configuration hits an errata of the internal IP core.
+
+ +-------------------------------+
+ | SoC |
+ | | +-----+ +-----+
+ | +------------+ | | dev | | dev |
+ | |I2C IP Core1|--\ | +-----+ +-----+
+ | +------------+ \-------+ | | |
+ | |Pinctrl|--|------+--------+
+ | +------------+ +-------+ |
+ | |I2C IP Core2|--/ |
+ | +------------+ |
+ | |
+ +-------------------------------+
+
+Required properties:
+- compatible: "i2c-demux-pinctrl"
+- i2c-parent: List of phandles of I2C masters available for selection. The
first
+ one will be used as default.
+- i2c-bus-name: The name of this bus. Also needed as pinctrl-name for the I2C
+ parents.
+
+Furthermore, I2C mux properties and child nodes. See mux.txt in this directory.
+
+Example:
+
+Here is a snipplet for a bus to be demuxed. It contains various i2c clients for
+HDMI, so the bus is named "i2c-hdmi":
+
+ i2chdmi: i2c@8 {
+
+ compatible = "i2c-demux-pinctrl";
+ i2c-parent = <&gpioi2c>, <&iic2>, <&i2c2>;
+ i2c-bus-name = "i2c-hdmi";
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ ak4643: sound-codec@12 {
+ compatible = "asahi-kasei,ak4643";
+
+ #sound-dai-cells = <0>;
+ reg = <0x12>;
+ };
+
+ composite-in@20 {
+ compatible = "adi,adv7180";
+ reg = <0x20>;
+ remote = <&vin1>;
+
+ port {
+ adv7180: endpoint {
+ bus-width = <8>;
+ remote-endpoint = <&vin1ep0>;
+ };
+ };
+ };
+
+ hdmi@39 {
+ compatible = "adi,adv7511w";
+ reg = <0x39>;
+ interrupt-parent = <&gpio1>;
+ interrupts = <15 IRQ_TYPE_LEVEL_LOW>;
+
+ adi,input-depth = <8>;
+ adi,input-colorspace = "rgb";
+ adi,input-clock = "1x";
+ adi,input-style = <1>;
+ adi,input-justification = "evenly";
+
+ ports {
+ #address-cells = <1>;
+ #size-cells = <0>;
+
+ port@0 {
+ reg = <0>;
+ adv7511_in: endpoint {
+ remote-endpoint =
<&du_out_lvds0>;
+ };
+ };
+
+ port@1 {
+ reg = <1>;
+ adv7511_out: endpoint {
+ remote-endpoint = <&hdmi_con>;
+ };
+ };
+ };
+ };
+ };
+
+And for clarification, here are the snipplets for the i2c-parents:
+
+ gpioi2c: i2c@9 {
+ #address-cells = <1>;
+ #size-cells = <0>;
+ compatible = "i2c-gpio";
+ status = "disabled";
+ gpios = <&gpio5 6 GPIO_ACTIVE_HIGH /* sda */
+ &gpio5 5 GPIO_ACTIVE_HIGH /* scl */
+ >;
+ i2c-gpio,delay-us = <5>;
+ };
+
+...
+
+&i2c2 {
+ pinctrl-0 = <&i2c2_pins>;
+ pinctrl-names = "i2c-hdmi";
+
+ clock-frequency = <100000>;
+};
+
+...
+
+&iic2 {
+ pinctrl-0 = <&iic2_pins>;
+ pinctrl-names = "i2c-hdmi";
+
+ clock-frequency = <100000>;
+};
+
+Please note:
+
+- pinctrl properties for the parent I2C controllers need a pinctrl state
+ with the same name as i2c-bus-name, not "default"!
+
+- the i2c masters must have their status "disabled". This driver will
+ enable them at runtime when needed.
+
+Changing I2C controllers:
+
+The created mux-device will have a file "cur_master" in its sysfs-entry. Write
+0 there for the first master listed in the "i2c-parent" property, 1 for the
+second etc. Reading the file will give you a list with the active master
+marked. Example from a Renesas Lager board:
+
+root@Lager:~# cat /sys/bus/platform/devices/i2c@8/cur_master
+* 0 - /i2c@9
+ 1 - /i2c@e6520000
+ 2 - /i2c@e6530000
+
+root@Lager:~# echo 2 > /sys/bus/platform/devices/i2c@8/cur_master
+
+root@Lager:~# cat /sys/bus/platform/devices/i2c@8/cur_master
+ 0 - /i2c@9
+ 1 - /i2c@e6520000
+* 2 - /i2c@e6530000
+
--
2.1.4
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