linux-kernel - Re: [PATCH 03/11] dt-bindings: interrupt-controller: RISC-V PLIC documentation

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Date:   Mon, 6 Aug 2018 14:59:48 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     atish.patra@....com
Cc:     Christoph Hellwig <hch@....de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...ive.com>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        devicetree@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-riscv@...ts.infradead.org, Stafford Horne <shorne@...il.com>
Subject: Re: [PATCH 03/11] dt-bindings: interrupt-controller: RISC-V PLIC documentation

On Thu, Aug 2, 2018 at 4:08 PM Atish Patra <atish.patra@....com> wrote:
>
> On 8/2/18 4:50 AM, Christoph Hellwig wrote:
> > From: Palmer Dabbelt <palmer@...belt.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@...belt.com>
> > [hch: various fixes and updates]
> > Signed-off-by: Christoph Hellwig <hch@....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..c756cd208a93
> > --- /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)
>
> The one in the real device tree has two entries.
> reg = <0x00000000 0x0c000000 0x00000000 0x04000000>;
>
> Is it intentional or just incorrect entry left over from earlier days?

> > +             reg = <0xc000000 0x4000000>;

Looks to me like one has #size-cells and #address-cells set to 2 and
the example is using 1.

Rob