Re: [PATCH v1 1/3] dt-bindings: interrupt-controller: Require trigger type for T-HEAD PLIC

From: Guo Ren <guoren@kernel.org>
To: Samuel Holland <samuel@sholland.org>
Cc: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>,
	Prabhakar <prabhakar.csengg@gmail.com>,
	Marc Zyngier <maz@kernel.org>,
	Sagar Kadam <sagar.kadam@sifive.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	linux-renesas-soc@vger.kernel.org,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Thomas Gleixner <tglx@linutronix.de>,
	Biju Das <biju.das.jz@bp.renesas.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Rob Herring <robh+dt@kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-riscv <linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v1 1/3] dt-bindings: interrupt-controller: Require trigger type for T-HEAD PLIC
Date: Mon, 27 Jun 2022 15:40:25 +0800	[thread overview]
Message-ID: <CAJF2gTSq1NsBWRCg+kpTbJRwSeE30P9NVB5di6vzi7m2CFRzHw@mail.gmail.com> (raw)
In-Reply-To: <20220627051257.38543-2-samuel@sholland.org>

On Mon, Jun 27, 2022 at 1:13 PM Samuel Holland <samuel@sholland.org> wrote:
>
> The RISC-V PLIC specification unfortunately allows PLIC implementations
> to ignore edges seen while an edge-triggered interrupt is being handled:
>
>   Depending on the design of the device and the interrupt handler,
>   in between sending an interrupt request and receiving notice of its
>   handler’s completion, the gateway might either ignore additional
>   matching edges or increment a counter of pending interrupts.
>
> For PLICs with that misfeature, software needs to know the trigger type
> of each interrupt. This allows it to work around the issue by completing
> edge-triggered interrupts before handling them. Such a workaround is
> required to avoid missing any edges.
>
> The T-HEAD C9xx PLIC is an example of a PLIC with this behavior.
Actually, C9xx support pulse signals which configed by
pad_plic_int_cfg_x for SoC vendor:

https://github.com/T-head-Semi/openc906/blob/main/C906_RTL_FACTORY/gen_rtl/plic/rtl/plic_int_kid.v
104: assign int_new_pending = pad_plic_int_cfg_x ? int_pulse
105:
        : level_int_pending;

They could put pad_plic_int_cfg_x into the SoC software config
registers region or bind them to constant values.

>
> Signed-off-by: Samuel Holland <samuel@sholland.org>
> ---
>
>  .../sifive,plic-1.0.0.yaml                    | 31 ++++++++++++++++---
>  1 file changed, 27 insertions(+), 4 deletions(-)
>
> 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 27092c6a86c4..3c589cbca851 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
> @@ -26,9 +26,13 @@ description:
>    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.
> +  The PLIC supports both edge-triggered and level-triggered interrupts. For
> +  edge-triggered interrupts, the RISC-V PLIC spec allows two responses to edges
> +  seen while an interrupt handler is active; the PLIC may either queue them or
> +  ignore them. In the first case, handlers are oblivious to the trigger type, so
> +  it is not included in the interrupt specifier. In the second case, software
> +  needs to know the trigger type, so it can reorder the interrupt flow to avoid
> +  missing interrupts.
>
>    While the RISC-V ISA doesn't specify a memory layout for the PLIC, the
>    "sifive,plic-1.0.0" device is a concrete implementation of the PLIC that
> @@ -65,7 +69,8 @@ properties:
>      const: 0
>
>    '#interrupt-cells':
> -    const: 1
> +    minimum: 1
> +    maximum: 2
>
>    interrupt-controller: true
>
> @@ -91,6 +96,24 @@ required:
>    - interrupts-extended
>    - riscv,ndev
>
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          contains:
> +            enum:
> +              - thead,c900-plic
> +
> +    then:
> +      properties:
> +        '#interrupt-cells':
> +          const: 2
> +
> +    else:
> +      properties:
> +        '#interrupt-cells':
> +          const: 1
> +
>  additionalProperties: false
>
>  examples:
> --
> 2.35.1
>

-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/