98 lines
3 KiB
Plaintext
98 lines
3 KiB
Plaintext
* Open PIC Binding
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This binding specifies what properties must be available in the device tree
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representation of an Open PIC compliant interrupt controller. This binding is
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based on the binding defined for Open PIC in [1] and is a superset of that
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binding.
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Required properties:
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NOTE: Many of these descriptions were paraphrased here from [1] to aid
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readability.
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- compatible: Specifies the compatibility list for the PIC. The type
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shall be <string> and the value shall include "open-pic".
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- reg: Specifies the base physical address(s) and size(s) of this
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PIC's addressable register space. The type shall be <prop-encoded-array>.
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- interrupt-controller: The presence of this property identifies the node
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as an Open PIC. No property value shall be defined.
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- #interrupt-cells: Specifies the number of cells needed to encode an
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interrupt source. The type shall be a <u32> and the value shall be 2.
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- #address-cells: Specifies the number of cells needed to encode an
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address. The type shall be <u32> and the value shall be 0. As such,
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'interrupt-map' nodes do not have to specify a parent unit address.
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Optional properties:
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- pic-no-reset: The presence of this property indicates that the PIC
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shall not be reset during runtime initialization. No property value shall
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be defined. The presence of this property also mandates that any
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initialization related to interrupt sources shall be limited to sources
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explicitly referenced in the device tree.
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* Interrupt Specifier Definition
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Interrupt specifiers consists of 2 cells encoded as
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follows:
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- <1st-cell>: The interrupt-number that identifies the interrupt source.
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- <2nd-cell>: The level-sense information, encoded as follows:
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0 = low-to-high edge triggered
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1 = active low level-sensitive
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2 = active high level-sensitive
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3 = high-to-low edge triggered
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* Examples
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Example 1:
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/*
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* An Open PIC interrupt controller
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*/
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mpic: pic@40000 {
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// This is an interrupt controller node.
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interrupt-controller;
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// No address cells so that 'interrupt-map' nodes which reference
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// this Open PIC node do not need a parent address specifier.
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#address-cells = <0>;
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// Two cells to encode interrupt sources.
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#interrupt-cells = <2>;
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// Offset address of 0x40000 and size of 0x40000.
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reg = <0x40000 0x40000>;
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// Compatible with Open PIC.
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compatible = "open-pic";
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// The PIC shall not be reset.
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pic-no-reset;
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};
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Example 2:
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/*
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* An interrupt generating device that is wired to an Open PIC.
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*/
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serial0: serial@4500 {
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// Interrupt source '42' that is active high level-sensitive.
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// Note that there are only two cells as specified in the interrupt
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// parent's '#interrupt-cells' property.
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interrupts = <42 2>;
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// The interrupt controller that this device is wired to.
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interrupt-parent = <&mpic>;
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};
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* References
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[1] Devicetree Specification
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(https://www.devicetree.org/specifications/)
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