Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq() and its ilk

[Marc Zyngier <maz@kernel.org>]

[Adding Geert]

On Sat, 06 Nov 2021 20:26:47 +0000,
Sergey Shtylyov <s.shtylyov@omp.ru> wrote:
> 
> 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!
> 
> Fixes: a85a6c86c25b ("driver core: platform: Clarify that IRQ 0 is invalid")
> Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
> 
> ---
> The patch is against the 'driver-core-linus' branch of Greg Kroah-Hartman's
> 'driver-core.git' repo.
> 
>  drivers/base/platform.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Index: driver-core/drivers/base/platform.c
> ===================================================================
> --- 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 = -ENXIO;
>  out:
> -	WARN(ret == 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
>  
>  	r = platform_get_resource_byname(dev, IORESOURCE_IRQ, name);
>  	if (r) {
> -		WARN(r->start == 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.

From 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.

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