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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 12 Oct 2022 10:22:08 -0700
Message-ID: <CAHk-=wg2Pkb9kbfbstbB91AJA2SF6cySbsgHG-iQMq56j3VTcA@mail.gmail.com>
Subject: Re: [GIT PULL] virtio: fixes, features
To:     "Michael S. Tsirkin" <mst@redhat.com>
Cc:     Michael Ellerman <mpe@ellerman.id.au>, kvm@vger.kernel.org,
        virtualization@lists.linux-foundation.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, alvaro.karsz@solid-run.com,
        angus.chen@jaguarmicro.com, gavinl@nvidia.com, jasowang@redhat.com,
        lingshan.zhu@intel.com, wangdeming@inspur.com,
        xiujianfeng@huawei.com, linuxppc-dev@lists.ozlabs.org,
        linux-pci@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>
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On Wed, Oct 12, 2022 at 8:51 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> Are you sure?

MichaelE is right.

This is just bogus historical garbage:

> arch/arm/include/asm/irq.h:#ifndef NO_IRQ
> arch/arm/include/asm/irq.h:#define NO_IRQ       ((unsigned int)(-1))

that I've tried to get rid of for years, but for some reason it just won't die.

NO_IRQ should be zero. Or rather, it shouldn't exist at all. It's a bogus thing.

You can see just how bogus it is from grepping for it - the users are
all completely and utterly confused, and all are entirely historical
brokenness.

The correct way to check for "no irq" doesn't use NO_IRQ at all, it just does

        if (dev->irq) ...

which is why you will only find a few instances of NO_IRQ in the tree
in the first place.

The NO_IRQ thing is mainly actually defined by a few drivers that just
never got converted to the proper world order, and even then you can
see the confusion (ie some drivers use "-1", others use "0", and yet
others use "((unsigned int)(-1)".

                   Linus