linux-kernel - Re: [PATCH 2/3] dts: RISC-V local interrupt controller docs

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Date:   Tue, 4 Jul 2017 12:18:12 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com,
        robh+dt@...nel.org, jic23@...nel.org, treding@...dia.com,
        maxime.ripard@...e-electrons.com, marek.vasut@...il.com,
        ccc94453@....cybercity.dk, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 2/3] dts: RISC-V local interrupt controller docs

On Mon, Jun 26, 2017 at 10:21:23PM -0700, Palmer Dabbelt wrote:
> This patch adds 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>
> ---
>  .../interrupt-controller/riscv,cpu-intc.txt        | 70 ++++++++++++++++++++++
>  1 file changed, 70 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..f4906f49a1b4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt
> @@ -0,0 +1,70 @@
> +RISC-V Hart-Level Interrupt Controller (HLIC)
> +---------------------------------------------
> +
> +RISC-V cores include Control Status Registers (CSRs) which are local to each
> +hart 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 specifices 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 architectually mandated real-time timer that is
> +controller via SBI calls and CSR reads.  External interrupts connect all other
> +device interrupts to the HLIC, which are routed via the platforw-level
> +interrupt contrellor (PLIC).
> +
> +All RISC-V systems that conform to the supervisor ISA specification are
> +required to have a HLIC with these three interrupt sources present.
> +
> +Required properties:
> +- compatible : "riscv,cpu-intc"
> +- #interrupt-cells : should be <1>

I know this'll sound trivial, but it would be worth defining what that
cell encodes. I guess it corresponds to a particular HW(?) notion of
interrupt ID -- it would be worth calling out which one.

> +- 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 of a device tree entry for a standard RISC-V hart is as follows:
> +
> +	cpu1: cpu@1 {
> +		clock-frequency = <1600000000>;
> +		compatible = "riscv";
> +		d-cache-block-size = <64>;
> +		d-cache-sets = <64>;
> +		d-cache-size = <16384>;
> +		d-tlb-sets = <1>;
> +		d-tlb-size = <32>;
> +		device_type = "cpu";
> +		i-cache-block-size = <64>;
> +		i-cache-sets = <64>;
> +		i-cache-size = <16384>;
> +		i-tlb-sets = <1>;
> +		i-tlb-size = <32>;
> +		mmu-type = "riscv,sv39";
> +		next-level-cache = <&L2>;
> +		reg = <1>;
> +		riscv,isa = "rv64imac";
> +		status = "okay";
> +		tlb-split;
> +		cpu1-intc: interrupt-controller {
> +			#interrupt-cells = <1>;
> +			compatible = "riscv,cpu-intc";
> +			interrupt-controller;
> +		};
> +	};

As with Rob's comments, you'll need to document the RISC-V cpu binding,
as we do for ARM in Documentation/devicetree/bindings/arm/cpus.txt. That
should describe the format of your reg entry, which common properties
are meaningful, and any RISC-V specific properties or values.

I also don't see anything like an enable-method. Is your SMP bringup
mechanism defined by the architecture?

Thanks,
Mark.