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

From: Marc Zyngier <maz@kernel.org>
To: Icenowy Zheng <uwu@icenowy.me>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Samuel Holland <samuel@sholland.org>,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
Subject: Re: [PATCH] irqchip/sifive-plic: drop quirk for two-cell variant
Date: Tue, 22 Nov 2022 17:28:18 +0000	[thread overview]
Message-ID: <86o7syoq4t.wl-maz@kernel.org> (raw)
In-Reply-To: <20221121042026.419383-1-uwu@icenowy.me>

On Mon, 21 Nov 2022 04:20:26 +0000,
Icenowy Zheng <uwu@icenowy.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.

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