linux-kernel - Re: [PATCH v4 1/3] dt-bindings: interrupt-controller: RISC-V local interrupt controller

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Message-ID: <20180813153648.GA29089@rob-hp-laptop>
Date:   Mon, 13 Aug 2018 09:36:48 -0600
From:   Rob Herring <robh@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     tglx@...utronix.de, palmer@...ive.com, jason@...edaemon.net,
        marc.zyngier@....com, mark.rutland@....com, anup@...infault.org,
        atish.patra@....com, devicetree@...r.kernel.org,
        aou@...s.berkeley.edu, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, shorne@...il.com,
        Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [PATCH v4 1/3] dt-bindings: interrupt-controller: RISC-V local
 interrupt controller

On Thu, Aug 09, 2018 at 09:56:00AM +0200, Christoph Hellwig wrote:
> From: Palmer Dabbelt <palmer@...belt.com>
> 
> Add documentation on the RISC-V local interrupt controller, which is a
> per-hart interrupt controller that manages all interrupts entering a
> RISC-V hart.  This interrupt controller is present on all RISC-V systems.
> 
> Signed-off-by: Palmer Dabbelt <palmer@...belt.com>
> [hch: minor cleanups]
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  .../interrupt-controller/riscv,cpu-intc.txt   | 44 +++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt
> 
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt b/Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt
> new file mode 100644
> index 000000000000..b0a8af51c388
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt
> @@ -0,0 +1,44 @@
> +RISC-V Hart-Level Interrupt Controller (HLIC)
> +---------------------------------------------
> +
> +RISC-V cores include Control Status Registers (CSRs) which are local to each
> +CPU core (HART in RISC-V terminology) and can be read or written by software.
> +Some of these CSRs are used to control local interrupts connected to the core.
> +Every interrupt is ultimately routed through a hart's HLIC before it
> +interrupts that hart.
> +
> +The RISC-V supervisor ISA manual specifies three interrupt sources that are
> +attached to every HLIC: software interrupts, the timer interrupt, and external
> +interrupts.  Software interrupts are used to send IPIs between cores.  The
> +timer interrupt comes from an architecturally mandated real-time timer that is
> +controller via Supervisor Binary Interface (SBI) calls and CSR reads.  External

s/controller/controlled/

> +interrupts connect all other device interrupts to the HLIC, which are routed
> +via the platform-level interrupt controller (PLIC).
> +
> +All RISC-V systems that conform to the supervisor ISA specification are
> +required to have a HLIC with these three interrupt sources present.  Since the
> +interrupt map is defined by the ISA it's not listed in the HLIC's device tree
> +entry, though external interrupt controllers (like the PLIC, for example) will
> +need to define how their interrupts map to the relevant HLICs.  This means
> +a PLIC interrupt property will typically list the HLICs for all present HARTs
> +in the system.
> +
> +Required properties:
> +- compatible : "riscv,cpu-intc"
> +- #interrupt-cells : should be <1>

Given that there's only 3 sources and they are fixed(?), you should 
define the numbering of them here.

> +- interrupt-controller : Identifies the node as an interrupt controller
> +
> +Furthermore, this interrupt-controller MUST be embedded inside the cpu
> +definition of the hart whose CSRs control these local interrupts.
> +
> +An example device tree entry for a HLIC is show below.
> +
> +	cpu1: cpu@1 {
> +		compatible = "riscv";
> +		...
> +		cpu1-intc: interrupt-controller {
> +			#interrupt-cells = <1>;
> +			compatible = "riscv,cpu-intc", "sifive,fu540-c000-cpu-intc";

The order here should be reversed (most specific first) and 
"sifive,fu540-c000-cpu-intc" needs to be listed above.

> +			interrupt-controller;
> +		};
> +	};
> -- 
> 2.18.0
>