linux-kernel - Re: [PATCH V3 1/2] dt-bindings: update riscv plic compatible string

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Date:   Thu, 14 Oct 2021 02:25:46 +0200
From:   Heiko Stuebner <heiko@...ech.de>
To:     Guo Ren <guoren@...nel.org>
Cc:     Anup Patel <anup@...infault.org>,
        Atish Patra <atish.patra@....com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...belt.com>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Rob Herring <robh@...nel.org>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH V3 1/2] dt-bindings: update riscv plic compatible string

Hi,

Am Mittwoch, 13. Oktober 2021, 14:49:57 CEST schrieb Guo Ren:
> On Wed, Oct 13, 2021 at 5:43 PM Heiko Stübner <heiko@...ech.de> wrote:
> >
> > Am Mittwoch, 13. Oktober 2021, 11:19:53 CEST schrieb Anup Patel:
> > > On Wed, Oct 13, 2021 at 2:44 PM Heiko Stübner <heiko@...ech.de> wrote:
> > > >
> > > > Am Mittwoch, 13. Oktober 2021, 11:11:26 CEST schrieb Anup Patel:
> > > > > On Wed, Oct 13, 2021 at 2:27 PM Heiko Stübner <heiko@...ech.de> wrote:
> > > > > >
> > > > > > Hi Anup,
> > > > > >
> > > > > > Am Mittwoch, 13. Oktober 2021, 07:11:46 CEST schrieb Anup Patel:
> > > > > > > On Wed, Oct 13, 2021 at 6:52 AM <guoren@...nel.org> wrote:
> > > > > > > >
> > > > > > > > From: Guo Ren <guoren@...ux.alibaba.com>
> > > > > > > >
> > > > > > > > Add the compatible string "thead,c900-plic" to the riscv plic
> > > > > > > > bindings to support SOCs with thead,c9xx processor cores.
> > > > > > > >
> > > > > > > > Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
> > > > > > > > Cc: Rob Herring <robh@...nel.org>
> > > > > > > > Cc: Palmer Dabbelt <palmerdabbelt@...gle.com>
> > > > > > > > Cc: Anup Patel <anup@...infault.org>
> > > > > > > > Cc: Atish Patra <atish.patra@....com>
> > > > > > > >
> > > > > > > > ---
> > > > > > > >
> > > > > > > > Changes since V3:
> > > > > > > >  - Rename "c9xx" to "c900"
> > > > > > > >  - Add thead,c900-plic in the description section
> > > > > > > > ---
> > > > > > > >  .../bindings/interrupt-controller/sifive,plic-1.0.0.yaml    | 6 ++++++
> > > > > > > >  1 file changed, 6 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> > > > > > > > index 08d5a57ce00f..82629832e5a5 100644
> > > > > > > > --- a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> > > > > > > > +++ b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> > > > > > > > @@ -35,6 +35,11 @@ description:
> > > > > > > >    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>.
> > > > > > > >
> > > > > > > > +  While the "thead,c900-plic" would mask IRQ with readl(claim), so it needn't
> > > > > > > > +  mask/unmask which needed in RISC-V PLIC. When in IRQS_ONESHOT & IRQCHIP_EOI_THREADED
> > > > > > > > +  path, unnecessary mask operation would cause a blocking irq bug in thead,c900-plic.
> > > > > > > > +  Because when IRQ is disabled in c900, writel(hwirq, claim) would be invalid.
> > > > > > >
> > > > > > > This is a totally incorrect description of the errata required for C9xx PLIC.
> > > > > > >
> > > > > > > Please don't project non-compliance as a feature of C9xx PLIC.
> > > > > > >
> > > > > > > > +
> > > > > > > >  maintainers:
> > > > > > > >    - Sagar Kadam <sagar.kadam@...ive.com>
> > > > > > > >    - Paul Walmsley  <paul.walmsley@...ive.com>
> > > > > > > > @@ -46,6 +51,7 @@ properties:
> > > > > > > >        - enum:
> > > > > > > >            - sifive,fu540-c000-plic
> > > > > > > >            - canaan,k210-plic
> > > > > > > > +          - thead,c900-plic
> > > > > >
> > > > > > we still want specific SoC names in the compatible, the "c900"
> > > > > > is still a sort-of placeholder.
> > > > >
> > > > > Yes, we need "c900" compatible string as well. The "c9xx"
> > > > > compatible string is for the custom PLIC spec followed by T-HEAD.
> > > >
> > > > What I meant was that the soc-specific string should name the
> > > > actual SoC (c906, c910) and not some imaginary chip ;-)
> > >
> > > Ahh, yes. It should be an actual soc name in the compatible
> > > string.
> > >
> > > For example, SiFive uses "fu540" string to identify some of the
> > > devices on both SiFive unleashed and SiFive unmatched boards.
> > >
> > > I was under the impression that "c900" is an actual SoC name.
> > >
> > > Regards,
> > > Anup
> > >
> > > >
> > > > See for example mali gpu bindings for a similar reference
> > > > in devicetree/bindings/gpu/arm,mali-bifrost.yaml .
> > > >
> > > >
> > > >
> > > >
> > > > >
> > > > > >
> > > > > >
> > > > > > > >        - const: sifive,plic-1.0.0
> > > > > > >
> > > > > > > The PLIC DT node requires two compatible string:
> > > > > > > <implementation_compat>, <spec_compat>
> > > > > > >
> > > > > > > The C9xx PLIC is not RISC-V PLIC so, the DT node should
> > > > > > > be: "thead,c900-plic", "thead,c9xx-plic"
> > > > > > >
> > > > > > > You need to change "- const: sifive,plic-1.0.0" to
> > > > > > > - enum:
> > > > > > >     - sifive,plic-1.0.0
> > > > > > >     - thead,c9xx-plic
> >
> > isn't XuanTie the series containing the c906 and c910?
> XuanTie contain two CPU series:
> riscv: c906, c910
> csky: c807, c810, c860
> 
> > So maybe
> >         thead,xuantie-plic
> > for the spec compatible.
> >
> > So doing in full
> >         compatible = "thead,c906-plic", "thead,xuantie-plic"
> How about:
> compatible = "allwinner,d1-plic", "thead,c900-plic"

This looks sensible.

- I guess the question in general is, is the PLIC part of the core spec
or part of the soc. In other words will all SoCs that use C9xx cores,
use this specific PLIC characteristic?

- If all C9xx-based SoCs will use this PLIC, I guess that thead,c900-plic
  in your compatible above sounds pretty good.

- Should it be thead,* or t-head,* for the vendor-prefix?
  (domain seems to be t-head.cn)


Heiko