dt-bindings: interrupt-controller: SiFive Plaform Level Interrupt Controller

SiFive Platform-Level Interrupt Controller (PLIC)

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SiFive SOCs include an implementation of the Platform-Level Interrupt Controller

(PLIC) high-level specification in the RISC-V Privileged Architecture

specification.  The PLIC connects all external interrupts in the system to all

hart contexts in the system, via the external interrupt source in each hart.

A hart context is a privilege mode in a hardware execution thread.  For example,

in an 4 core system with 2-way SMT, you have 8 harts and probably at least two

privilege modes per hart; machine mode and supervisor mode.

Each interrupt can be enabled on per-context basis.  Any context can claim

a pending enabled interrupt and then release it once it has been handled.

Each interrupt has a configurable priority.  Higher priority interrupts are

serviced first.  Each context can specify a priority threshold. Interrupts

with priority below this threshold will not cause the PLIC to raise its

interrupt line leading to the context.

While the PLIC supports both edge-triggered and level-triggered interrupts,

interrupt handlers are oblivious to this distinction and therefore it is not

specified in the PLIC device-tree binding.

While the RISC-V ISA doesn't specify a memory layout for the PLIC, the

"sifive,plic-1.0.0" device is a concrete implementation of the PLIC that

contains a specific memory layout, which is documented in chapter 8 of the

SiFive U5 Coreplex Series Manual <https://static.dev.sifive.com/U54-MC-RVCoreIP.pdf>.

Required properties:

- compatible : "sifive,plic-1.0.0" and a string identifying the actual

  detailed implementation in case that specific bugs need to be worked around.

- #address-cells : should be <0> or more.

- #interrupt-cells : should be <1> or more.

- interrupt-controller : Identifies the node as an interrupt controller.

- reg : Should contain 1 register range (address and length).

- interrupts-extended : Specifies which contexts are connected to the PLIC,

  with "-1" specifying that a context is not present.  Each node pointed

  to should be a riscv,cpu-intc node, which has a riscv node as parent.

- riscv,ndev: Specifies how many external interrupts are supported by

  this controller.

Example:

	plic: interrupt-controller@c000000 {

		#address-cells = <0>;

		#interrupt-cells = <1>;

		compatible = "sifive,plic-1.0.0", "sifive,fu540-c000-plic";

		interrupt-controller;

		interrupts-extended = <

			&cpu0-intc 11

			&cpu1-intc 11 &cpu1-intc 9

			&cpu2-intc 11 &cpu2-intc 9

			&cpu3-intc 11 &cpu3-intc 9

			&cpu4-intc 11 &cpu4-intc 9>;

		reg = <0xc000000 0x4000000>;

		riscv,ndev = <10>;

	};