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I2C MUXes described by the i2c-gpio-mux sometimes need a significant amount of time to switch from a bus to another. When a new bus is selected, the first I2C transfer can fail if it occurs too early. There is no way to describe this transition delay that has to be waited before starting the first I2C transfer. Add a 'settle-time-us' property that indicates the delay to be respected before doing the first i2c transfer. Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Reviewed-by: Andi Shyti <andi.shyti@kernel.org> Acked-by: Peter Rosin <peda@axentia.se> Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
108 lines
3.2 KiB
YAML
108 lines
3.2 KiB
YAML
# SPDX-License-Identifier: GPL-2.0-only
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%YAML 1.2
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---
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$id: http://devicetree.org/schemas/i2c/i2c-mux-gpio.yaml#
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$schema: http://devicetree.org/meta-schemas/core.yaml#
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title: GPIO-based I2C Bus Mux
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maintainers:
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- Wolfram Sang <wsa@kernel.org>
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description: |
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This binding describes an I2C bus multiplexer that uses GPIOs to route the I2C signals.
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+-----+ +-----+
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| dev | | dev |
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+------------+ +-----+ +-----+
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| SoC | | |
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| | /--------+--------+
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| +------+ | +------+ child bus A, on GPIO value set to 0
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| | I2C |-|--| Mux |
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| +------+ | +--+---+ child bus B, on GPIO value set to 1
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| | | \----------+--------+--------+
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| +------+ | | | | |
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| | GPIO |-|-----+ +-----+ +-----+ +-----+
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| +------+ | | dev | | dev | | dev |
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+------------+ +-----+ +-----+ +-----+
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For each I2C child node, an I2C child bus will be created. They will be numbered based on their
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order in the device tree.
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Whenever an access is made to a device on a child bus, the value set in the relevant node's reg
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property will be output using the list of GPIOs, the first in the list holding the least-
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significant value.
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If an idle state is defined, using the idle-state (optional) property, whenever an access is not
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being made to a device on a child bus, the GPIOs will be set according to the idle value.
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If an idle state is not defined, the most recently used value will be left programmed into
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hardware whenever no access is being made to a device on a child bus.
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properties:
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compatible:
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const: i2c-mux-gpio
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i2c-parent:
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description: phandle of the I2C bus that this multiplexer's master-side port is connected to
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$ref: /schemas/types.yaml#/definitions/phandle
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mux-gpios:
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description: list of GPIOs used to control the muxer
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minItems: 1
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maxItems: 4 # Should be enough
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idle-state:
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description: Value to set the muxer to when idle. When no value is given, it defaults to the
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last value used.
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$ref: /schemas/types.yaml#/definitions/uint32
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settle-time-us:
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description: Delay to wait before doing any transfer when a new bus gets selected.
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allOf:
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- $ref: i2c-mux.yaml
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unevaluatedProperties: false
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required:
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- compatible
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- i2c-parent
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- mux-gpios
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examples:
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- |
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i2cmux {
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compatible = "i2c-mux-gpio";
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#address-cells = <1>;
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#size-cells = <0>;
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mux-gpios = <&gpio1 22 0>, <&gpio1 23 0>;
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i2c-parent = <&i2c1>;
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i2c@1 {
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reg = <1>;
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#address-cells = <1>;
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#size-cells = <0>;
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ssd1307: oled@3c {
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compatible = "solomon,ssd1307fb-i2c";
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reg = <0x3c>;
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pwms = <&pwm 4 3000>;
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reset-gpios = <&gpio2 7 1>;
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};
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};
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i2c@3 {
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reg = <3>;
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#address-cells = <1>;
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#size-cells = <0>;
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pca9555: pca9555@20 {
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compatible = "nxp,pca9555";
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gpio-controller;
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#gpio-cells = <2>;
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reg = <0x20>;
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};
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};
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};
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