Subject: Re: [PATCH] platform: finally disallow IRQ0 in platform_get_irq() and
 its ilk
To:     Marc Zyngier <maz@kernel.org>
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>
References: <5e001ec1-d3f1-bcb8-7f30-a6301fd9930c@omp.ru>
 <87pmp7volh.wl-maz@kernel.org>
From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <c3bf828d-ac47-19f2-ee0b-ebf3105a38cb@omp.ru>
Date:   Tue, 4 Jan 2022 23:30:23 +0300
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Hello!

On 1/4/22 12:26 PM, Marc Zyngier 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.

   Yeah, valid IRQ0 on some SH boards -- which I believe could soon be addressed.

> 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:

   Of course, I'm prepared.

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

   Thank you!

MBR, Sergey