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> <9c3f9a6e-89b6-b73b-032f-e4b4ee6f72ac@omp.ru>
 <58caf8b54828bcc25cfc65220d29b68f@kernel.org>
From:   Sergey Shtylyov <s.shtylyov@omp.ru>
Organization: Open Mobile Platform
Message-ID: <c20818ab-9ed8-a26f-3298-9e5648b633ec@omp.ru>
Date:   Wed, 12 Jan 2022 23:08:53 +0300
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On 1/12/22 9:08 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.
>>>
>>> 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.

   Who argues with that? :-)
   However, I don't think it should be a pre-requisite for this patch,
so that we have extra time until 5.17 final... actually, I had couple
quick workarounds in mind; the problem however is that we don't seem to
have  the targets for testing... :-(

> Thanks,
> 
>         M.

MBR, Sergey