79 lines
2.2 KiB
Plaintext
79 lines
2.2 KiB
Plaintext
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Specifying GPIO information for devices
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============================================
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1) gpios property
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-----------------
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Nodes that makes use of GPIOs should specify them using one or more
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properties, each containing a 'gpio-list':
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gpio-list ::= <single-gpio> [gpio-list]
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single-gpio ::= <gpio-phandle> <gpio-specifier>
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gpio-phandle : phandle to gpio controller node
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gpio-specifier : Array of #gpio-cells specifying specific gpio
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(controller specific)
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GPIO properties should be named "[<name>-]gpios". Exact
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meaning of each gpios property must be documented in the device tree
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binding for each device.
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For example, the following could be used to describe gpios pins to use
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as chip select lines; with chip selects 0, 1 and 3 populated, and chip
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select 2 left empty:
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gpio1: gpio1 {
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gpio-controller
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#gpio-cells = <2>;
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};
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gpio2: gpio2 {
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gpio-controller
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#gpio-cells = <1>;
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};
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[...]
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chipsel-gpios = <&gpio1 12 0>,
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<&gpio1 13 0>,
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<0>, /* holes are permitted, means no GPIO 2 */
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<&gpio2 2>;
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Note that gpio-specifier length is controller dependent. In the
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above example, &gpio1 uses 2 cells to specify a gpio, while &gpio2
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only uses one.
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gpio-specifier may encode: bank, pin position inside the bank,
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whether pin is open-drain and whether pin is logically inverted.
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Exact meaning of each specifier cell is controller specific, and must
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be documented in the device tree binding for the device.
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Example of the node using GPIOs:
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node {
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gpios = <&qe_pio_e 18 0>;
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};
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In this example gpio-specifier is "18 0" and encodes GPIO pin number,
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and empty GPIO flags as accepted by the "qe_pio_e" gpio-controller.
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2) gpio-controller nodes
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------------------------
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Every GPIO controller node must both an empty "gpio-controller"
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property, and have #gpio-cells contain the size of the gpio-specifier.
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Example of two SOC GPIO banks defined as gpio-controller nodes:
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qe_pio_a: gpio-controller@1400 {
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#gpio-cells = <2>;
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compatible = "fsl,qe-pario-bank-a", "fsl,qe-pario-bank";
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reg = <0x1400 0x18>;
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gpio-controller;
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};
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qe_pio_e: gpio-controller@1460 {
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#gpio-cells = <2>;
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compatible = "fsl,qe-pario-bank-e", "fsl,qe-pario-bank";
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reg = <0x1460 0x18>;
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gpio-controller;
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};
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