Date:   Tue, 04 Jan 2022 09:26:18 +0000
Message-ID: <87pmp7volh.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Sergey Shtylyov <s.shtylyov@omp.ru>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq() and its ilk
In-Reply-To: <5e001ec1-d3f1-bcb8-7f30-a6301fd9930c@omp.ru>
References: <5e001ec1-d3f1-bcb8-7f30-a6301fd9930c@omp.ru>
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[Adding Geert]

On Sat, 06 Nov 2021 20:26:47 +0000,
Sergey Shtylyov <s.shtylyov@omp.ru> wrote:
>=20
> The commit a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is
> invalid") only calls WARN() when IRQ0 is about to be returned, however
> using IRQ0 is considered invalid (according to Linus) outside the arch/
> code where it's used by the i8253 drivers. Many driver subsystems treat
> 0 specially (e.g. as an indication of the polling mode by libata), so
> the users of platform_get_irq[_byname]() in them would have to filter
> out IRQ0 explicitly and this (quite obviously) doesn't scale...
> Let's finally get this straight and return -EINVAL instead of IRQ0!
>=20
> Fixes: a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invali=
d")
> Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
>=20
> ---
> The patch is against the 'driver-core-linus' branch of Greg Kroah-Hartman=
's
> 'driver-core.git' repo.
>=20
>  drivers/base/platform.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>=20
> Index: driver-core/drivers/base/platform.c
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> --- driver-core.orig/drivers/base/platform.c
> +++ driver-core/drivers/base/platform.c
> @@ -231,7 +231,8 @@ int platform_get_irq_optional(struct pla
>  out_not_found:
>  	ret =3D -ENXIO;
>  out:
> -	WARN(ret =3D=3D 0, "0 is an invalid IRQ number\n");
> +	if (WARN(!ret, "0 is an invalid IRQ number\n"))
> +		return -EINVAL;
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(platform_get_irq_optional);
> @@ -445,7 +446,8 @@ static int __platform_get_irq_byname(str
> =20
>  	r =3D platform_get_resource_byname(dev, IORESOURCE_IRQ, name);
>  	if (r) {
> -		WARN(r->start =3D=3D 0, "0 is an invalid IRQ number\n");
> +		if (WARN(!r->start, "0 is an invalid IRQ number\n"))
> +			return -EINVAL;
>  		return r->start;
>  	}

Geert recently mentioned that a few architectures (such as sh?) still
use IRQ0 as something valid in limited cases.

=46rom my PoV, this patch is fine, but please be prepared to fix things
in a couple of years when someone decides to boot a recent kernel on
their pet dinosaur. With that in mind:

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

--=20
Without deviation from the norm, progress is not possible.