MIME-Version: 1.0
Date:   Wed, 12 Jan 2022 18:08:43 +0000
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: <9c3f9a6e-89b6-b73b-032f-e4b4ee6f72ac@omp.ru>
References: <5e001ec1-d3f1-bcb8-7f30-a6301fd9930c@omp.ru>
 <87pmp7volh.wl-maz@kernel.org> <9c3f9a6e-89b6-b73b-032f-e4b4ee6f72ac@omp.ru>
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On 2022-01-12 17:53, Sergey Shtylyov wrote:
> On 1/4/22 12:26 PM, Marc Zyngier wrote:
> 
>> [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>
> 
>    Greg, so would that ACK be enough? Is there a chance this patch
> gets finally included
> into 5.17-rc1? Or should I look into fixing the recently found
> arch/sh/ issue 1st (as you
> can see, just WARN()'ing about IRQ0 wasn't enough to get this fixed)?

Fixing SH would be a good thing.

Thanks,

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