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

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Date:   Thu, 02 Aug 2018 13:30:01 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     christoph@...hmwalder.at, Christoph Hellwig <hch@...radead.org>
CC:     tglx@...utronix.de, jason@...edaemon.net, marc.zyngier@....com,
        robh+dt@...nel.org, mark.rutland@....com,
        devicetree@...r.kernel.org, aou@...s.berkeley.edu,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        shorne@...il.com
Subject:     Re: [PATCH 2/3] dt-bindings: interrupt-controller: RISC-V local interrupt controller docs

On Mon, 25 Jun 2018 13:04:48 PDT (-0700), christoph@...hmwalder.at wrote:
> On Fri, Jun 22, 2018 at 04:20:05PM -0700, Palmer Dabbelt wrote:
>> From: Palmer Dabbelt <palmer@...belt.com>
>>
>> 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        | 41 ++++++++++++++++++++++
>>  1 file changed, 41 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..61900e2e3868
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/interrupt-controller/riscv,cpu-intc.txt
>> @@ -0,0 +1,41 @@
>> +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 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 SBI calls and CSR reads.  External 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.
>> +
>> +Required properties:
>> +- compatible : "riscv,cpu-intc"
>> +- #interrupt-cells : should be <1>
>> +- 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.
>
> Spotted a typo here, "show" -> "shown".

Thanks.  It looks like we're actually dropping this binding and integrating 
this first-level interrupt controller into the core RISC-V arch code as keeping 
it split out results in too many inefficiencies.

>> +
>> +	cpu1: cpu@1 {
>> +		compatible = "riscv";
>> +		...
>> +		cpu1-intc: interrupt-controller {
>> +			#interrupt-cells = <1>;
>> +			compatible = "riscv,cpu-intc";
>> +			interrupt-controller;
>> +		};
>> +	};
>> --
>> 2.16.4
>
> Also, I've noticed that double spaces after punctuation are used pretty
> inconsistently throughout the document. Is that intended?

No.  I noticed this in the PLIC document as well, I'll fix that one up.

Thanks!