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Subject[PATCH 6/8] dt-bindings: interrupt-controller: RISC-V PLIC documentation
Date
From: Palmer Dabbelt <palmer@dabbelt.com>

This patch adds documentation for the platform-level interrupt
controller (PLIC) found in all RISC-V systems. This interrupt
controller routes interrupts from all the devices in the system to each
hart-local interrupt controller.

Note: the DTS bindings for the PLIC aren't set in stone yet, as we might
want to change how we're specifying holes in the hart list.

Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
[hch: various fixes and updates]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
.../interrupt-controller/sifive,plic0.txt | 57 +++++++++++++++++++
1 file changed, 57 insertions(+)
create mode 100644 Documentation/devicetree/bindings/interrupt-controller/sifive,plic0.txt

diff --git a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic0.txt b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic0.txt
new file mode 100644
index 000000000000..bbfa61cf8d3f
--- /dev/null
+++ b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic0.txt
@@ -0,0 +1,57 @@
+SiFive Platform-Level Interrupt Controller (PLIC)
+-------------------------------------------------
+
+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,plic0" 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,plic0".
+- #address-cells : should be <0>.
+- #interrupt-cells : should be <1>.
+- 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. The nodes pointed
+ to should be "riscv" HART nodes, or eventually be parented by such nodes.
+- riscv,ndev: Specifies how many external interrupts are supported by
+ this controller.
+
+Example:
+
+ plic: interrupt-controller@c000000 {
+ #address-cells = <0>;
+ #interrupt-cells = <1>;
+ compatible = "riscv,plic0";
+ 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>;
+ };
--
2.18.0
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