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

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Date:   Tue, 26 May 2020 17:32:30 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     seanga2@...il.com
CC:     anup@...infault.org, Anup Patel <Anup.Patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, robh+dt@...nel.org,
        daniel.lezcano@...aro.org, tglx@...utronix.de,
        devicetree@...r.kernel.org, Damien Le Moal <Damien.LeMoal@....com>,
        linux-kernel@...r.kernel.org, Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        linux-riscv@...ts.infradead.org
Subject:     Re: [PATCH 5/5] dt-bindings: timer: Add CLINT bindings

On Thu, 21 May 2020 23:29:36 PDT (-0700), seanga2@...il.com wrote:
> On 5/22/20 1:54 AM, Anup Patel wrote:
>> 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:
>>>> +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
>
> The PLIC seems to have its own RISC-V-sponsored documentation [1] which
> was split off from the older privileged specs. By your logic above,
> should it be renamed to riscv,plic0.txt (with a corresponding change in
> the documented compatible strings)?
>
> [1] https://github.com/riscv/riscv-plic-spec

Let's propose tagging that PLIC spec as v1.0.0 in the platform spec group, but
I don't see a reason why that wouldn't be viable.  Assuming that's all OK, we
can start calling this a RISC-V PLIC (in addition to a SiFive PLIC, as they'll
be compatible).

>> 
>> If RISC-V maintainers agree then I will document it as "RISC-V CLINT".
>> 
>> @Palmer ?? @Paul ??

The CLINT is a SiFive spec.  It has open source RTL so it's been implemented in
other designs, but it's not a RISC-V spec.  The CLIC, which is a superset of
the CLINT, is a RISC-V spec.  IIRC it's not finished yet (it's the fast
interrupts task group), but presumably we should have a "riscv,clic-2.0.0" (or
whatever it ends up being called) compat string to go along with the
specification.

>> Regards,
>> Anup
>> 
>
> --Sean