linux-kernel - Re: [PATCH 5/5] dt-bindings: timer: Add CLINT bindings

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Message-ID: <CAAhSdy0OuxCwMVPBrvPpYMfVrhUuY3pONysk75yognOM5-0U+g@mail.gmail.com>
Date:   Fri, 22 May 2020 11:24:07 +0530
From:   Anup Patel <anup@...infault.org>
To:     Sean Anderson <seanga2@...il.com>
Cc:     Anup Patel <anup.patel@....com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Rob Herring <robh+dt@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        devicetree@...r.kernel.org, Damien Le Moal <damien.lemoal@....com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 5/5] dt-bindings: timer: Add CLINT bindings

On Fri, May 22, 2020 at 1:35 AM Sean Anderson <seanga2@...il.com> wrote:
>
> On 5/21/20 9:45 AM, Anup Patel wrote:
> > We add DT bindings documentation for CLINT device.
> >
> > Signed-off-by: Anup Patel <anup.patel@....com>
> > ---
> >  .../bindings/timer/sifive,clint.txt           | 33 +++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/timer/sifive,clint.txt
> >
> > diff --git a/Documentation/devicetree/bindings/timer/sifive,clint.txt b/Documentation/devicetree/bindings/timer/sifive,clint.txt
> > new file mode 100644
> > index 000000000000..cae2dad1223a
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/timer/sifive,clint.txt
> > @@ -0,0 +1,33 @@
> > +SiFive Core Local Interruptor (CLINT)
> > +-------------------------------------
> > +
> > +SiFive (and other RISC-V) SOCs include an implementation of the SiFive Core
> > +Local Interruptor (CLINT) for M-mode timer and inter-processor interrupts.
> > +
> > +It directly connects to the timer and inter-processor interrupt lines of
> > +various HARTs (or CPUs) so RISC-V per-HART (or per-CPU) local interrupt
> > +controller is the parent interrupt controller for CLINT device.
> > +
> > +The clock frequency of CLINT is specified via "timebase-frequency" DT
> > +property of "/cpus" DT node. The "timebase-frequency" DT property is
> > +described in: Documentation/devicetree/bindings/riscv/cpus.yaml
> > +
> > +Required properties:
> > +- compatible : "sifive,clint-1.0.0" and a string identifying the actual
> > +  detailed implementation in case that specific bugs need to be worked around.
>
> Should the "riscv,clint0" compatible string be documented here? This

Yes, I forgot to add this compatible string. I will add in v2.

> peripheral is not really specific to sifive, as it is present in most
> rocket-chip cores.

I agree that CLINT is present in a lot of non-SiFive RISC-V SOCs and
FPGAs but this IP is only documented as part of SiFive FU540 SOC.
(Refer, https://static.dev.sifive.com/FU540-C000-v1.0.pdf)

The RISC-V foundation should host the CLINT spec independently
under https://github.com/riscv and make CLINT spec totally open.

For now, I have documented it just like PLIC DT bindings found at:
Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.txt

If RISC-V maintainers agree then I will document it as "RISC-V CLINT".

@Palmer ?? @Paul ??

>
> > +- reg : Should contain 1 register range (address and length).
> > +- interrupts-extended : Specifies which HARTs (or CPUs) are connected to
> > +  the CLINT.  Each node pointed to should be a riscv,cpu-intc node, which
> > +  has a riscv node as parent.
> > +
> > +Example:
> > +
> > +     clint@...0000 {
> > +             compatible = "sifive,clint-1.0.0", "sifive,fu540-c000-clint";
> > +             interrupts-extended = <
> > +                     &cpu1-intc 3 &cpu1-intc 7
> > +                     &cpu2-intc 3 &cpu2-intc 7
> > +                     &cpu3-intc 3 &cpu3-intc 7
> > +                     &cpu4-intc 3 &cpu4-intc 7>;
> > +             reg = <0x2000000 0x4000000>;
> > +     };
> >
>
> --Sean

Regards,
Anup