linux-kernel - Re: [PATCH v2 2/2] irqchip/sifive-plic: Add support for Renesas RZ/Five SoC

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Date:   Wed, 29 Jun 2022 16:00:22 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Pavel Machek <pavel@....cz>
Cc:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [PATCH v2 2/2] irqchip/sifive-plic: Add support for Renesas
 RZ/Five SoC

On 2022-06-29 14:41, Pavel Machek wrote:
> Hi!
> 
>> > >> +#define PLIC_QUIRK_EDGE_INTERRUPT      BIT(0)
>> > >>
>> > >>  struct plic_priv {
>> > >>         struct cpumask lmask;
>> > >>         struct irq_domain *irqdomain;
>> > >>         void __iomem *regs;
>> > >> +       u32 plic_quirks;
>> > >>  };
>> > >>
>> > >> What about something like above?
>> > >
>> > > LGTM.
>> > >
>> > > Marc suggested to make this unsigned long, but TBH, that won't make
>> > > much of a difference.  PLICs are present on RV32 SoCs, too, so you
>> > > cannot rely on having more than 32 bits anyway.
>> >
>> > But it will make a difference on a 64bit platform, as we want to
>> > use test_bit() and co to check for features.
>> >
>> Ok will change that to unsigned long and use the test_bit/set_bit 
>> instead.
> 
> Is there good enough reason for that? test_bit/... are when you need
> atomicity, and that's not the case here. Plain old & ... should be
> enough.

On any save architecture, '&' and test_bit() are the same thing.
Only RMW operations require atomicity.

'unsigned long' is is.

         M.
-- 
Jazz is not dead. It just smells funny...