linux-kernel - Re: [PATCH V4 2/3] dt-bindings: update riscv plic compatible string

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Message-ID: <1708236.01x493v0YS@phil>
Date:   Sat, 16 Oct 2021 18:31:47 +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>,
        Rob Herring <robh@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Guo Ren <guoren@...ux.alibaba.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH V4 2/3] dt-bindings: update riscv plic compatible string

Am Samstag, 16. Oktober 2021, 14:56:51 CEST schrieb Guo Ren:
> On Sat, Oct 16, 2021 at 6:35 PM Heiko Stuebner <heiko@...ech.de> wrote:
> >
> > Hi Guo,
> >
> > Am Samstag, 16. Oktober 2021, 05:21:59 CEST schrieb guoren@...nel.org:
> > > From: Guo Ren <guoren@...ux.alibaba.com>
> > >
> > > Add the compatible string "thead,c900-plic" to the riscv plic
> > > bindings to support allwinner d1 SOC which contains c906 core.
> >
> > The compatible strings sound good now, but some things below
> >
> > >
> > > 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 V4:
> > >  - Update description in errata style
> > >  - Update enum suggested by Anup, Heiko, Samuel
> > >
> > > Changes since V3:
> > >  - Rename "c9xx" to "c900"
> > >  - Add thead,c900-plic in the description section
> > > ---
> > >  .../interrupt-controller/sifive,plic-1.0.0.yaml       | 11 ++++++++++-
> > >  1 file changed, 10 insertions(+), 1 deletion(-)
> > >
> > > 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..272f29540135 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 +35,12 @@ 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>.
> > >
> > > +  The C9xx PLIC does not comply with the interrupt claim/completion process defined
> > > +  by the RISC-V PLIC specification because C9xx PLIC will mask an IRQ when it is
> > > +  claimed by PLIC driver (i.e. readl(claim) and the IRQ will be unmasked upon
> > > +  completion by PLIC driver (i.e. writel(claim). This behaviour breaks the handling
> > > +  of IRQS_ONESHOT by the generic handle_fasteoi_irq() used in the PLIC driver.
> > > +
> > >  maintainers:
> > >    - Sagar Kadam <sagar.kadam@...ive.com>
> > >    - Paul Walmsley  <paul.walmsley@...ive.com>
> > > @@ -46,7 +52,10 @@ properties:
> > >        - enum:
> > >            - sifive,fu540-c000-plic
> > >            - canaan,k210-plic
> > > -      - const: sifive,plic-1.0.0
> > > +      - enmu:
> >
> >         ^ spelling enum
> >
> > > +          - sifive,plic-1.0.0
> > > +          - thead,c900-plic
> > > +          - allwinner,sun20i-d1-plic
> >
> > but in general I'd think that you want something like
> >
> >   compatible:
> >     oneOf:
> >       - items:
> >           - enum:
> >               - sifive,fu540-c000-plic
> >               - canaan,k210-plic
> >           - const: sifive,plic-1.0.0
> >       - items:
> >           - enum:
> >               - allwinner,sun20i-d1-plic
> >           - const: thead,c900-plic
> >
> > Having only one item list would allow as valid combinations like
> > "sifive,fu540-c000-plic", "thead,c900-plic" when checking the schema.
> >
> > With the oneOf and separate lists we can make sure that such
> > "illegal" combinations get flagged by the dtbs_check
> >
> > [the enum with the single allwinner entry already leaves
> >  room for later addition to the c900-plic variant]
> Thx, I'll fix it in the next version.
> 
> another question: Is the allwinner_sun20i_d1_plic needed to IRQCHIP_DECLARE?
> 
> +IRQCHIP_DECLARE(thead_c900_plic, "thead,c900-plic", thead_c900_plic_init);
> +IRQCHIP_DECLARE(allwinner_sun20i_d1_plic, "allwinner,sun20i-d1-plic",
> thead_c900_plic_init);

Doing
	IRQCHIP_DECLARE(thead_c900_plic, "thead,c900-plic", thead_c900_plic_init);
should be enough for now.

Compatible-parsing happens from left to right, from most-specific to
most-generic. So having the allwinner-d1 compatible in there is sort of a
safeguard.

If at some _later point in time_ , some specific new quirk of the D1
implementation comes to light, we can _then_ just add a 
	IRQCHIP_DECLARE(allwinner_d1_plic, "allwinner,sun20i-d1-plic", allwinner_d1_plic_init);

Devicetrees should be stable and newer kernels should work with old
devicetrees, so having the soc-specific compatible in there just makes it
future proof :-)


Heiko