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SubjectRe: [PATCH v1 1/3] dt-bindings: interrupt-controller: Require trigger type for T-HEAD PLIC
Reviewed-by: Guo Ren <guoren@kernel.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.
>
> 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/

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