linux-kernel - Re: [PATCH] irqchip/sifive-plic: drop quirk for two-cell variant

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Date:   Tue, 22 Nov 2022 17:28:18 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Icenowy Zheng <uwu@...nowy.me>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Samuel Holland <samuel@...lland.org>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] irqchip/sifive-plic: drop quirk for two-cell variant

On Mon, 21 Nov 2022 04:20:26 +0000,
Icenowy Zheng <uwu@...nowy.me> wrote:
> 
> As the special handling of edge-triggered interrupts are defined in the
> PLIC spec, we can assume it's not a quirk, but a feature of the PLIC
> spec; thus making it a quirk and use quirk-based codepath is not so
> necessary.

It *is* necessary.

> 
> Move to a #interrupt-cells-based practice which will allow both device
> trees without interrupt flags and with interrupt flags work for all
> compatible strings.

No. You're tying together two unrelated concepts:

- Edges get dropped in some implementations (and only some). You can
  argue that the architecture allows it, but I see it is an
  implementation bug.

- The need for expressing additional information in the interrupt
  specifier is not necessarily related to the above. Other interrupt
  controllers use extra cells to encode the interrupt affinity, for
  example.

I want these two things to be kept separate. Otherwise, once we get
some fancy ACPI support for RISCV (no, please...), we'll have to redo
the whole thing...

> In addition, this addresses a stable version DT binding violation --
> Linux v5.19 comes with "thead,c900-plic" with #interrupt-cells defined to
> be 1 instead of 2, this commit will allow DTs that complies to Linux
> v5.19 binding work (although no such DT is devliered to the public now).

*That* is what should get fixed.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.