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Date:   Fri, 13 Mar 2020 16:56:42 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Marc Gonzalez <marc.w.gonzalez@free.fr>,
        Aman Sharma <amanharitsh123@gmail.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Andrew Murray <amurray@thegoodpenguin.co.uk>,
        Linus Walleij <linus.walleij@linaro.org>,
        Ryder Lee <ryder.lee@mediatek.com>,
        Karthikeyan Mitran <m.karthikeyan@mobiveil.co.in>,
        Hou Zhiqiang <Zhiqiang.Hou@nxp.com>,
        Mans Rullgard <mans@mansr.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org,
        Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH 4/5] pci: handled return value of platform_get_irq
 correctly
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On Fri, Mar 13, 2020 at 10:05:58PM +0100, Thomas Gleixner wrote:
> Bjorn Helgaas <helgaas@kernel.org> writes:
> > On Thu, Mar 12, 2020 at 10:53:06AM +0100, Marc Gonzalez wrote:
> >> Last time around, my understanding was that, going forward,
> >> the best solution was:
> >> 
> >> 	virq = platform_get_irq(...)
> >> 	if (virq <= 0)
> >> 		return virq ? : -ENODEV;
> >> 
> >> i.e. map 0 to -ENODEV, pass other errors as-is, remove the dev_err
> >> 
> >> @Bjorn/Lorenzo did you have a change of heart?
> >
> > Yes.  In 10006651 (Oct 20, 2017), I thought:
> >
> >   irq = platform_get_irq(pdev, 0);
> >   if (irq <= 0)
> >     return -ENODEV;
> >
> > was fine.  In 11066455 (Aug 7, 2019), I said I thought I was wrong and
> > that:
> >
> >   platform_get_irq() is a generic interface and we have to be able to
> >   interpret return values consistently.  The overwhelming consensus
> >   among platform_get_irq() callers is to treat "irq < 0" as an error,
> >   and I think we should follow suit.
> >   ...
> >   I think the best pattern is:
> >
> >     irq = platform_get_irq(pdev, i);
> >     if (irq < 0)
> >       return irq;
> 
> Careful. 0 is not a valid interrupt.

Should callers of platform_get_irq() check for a 0 return value?
About 900 of them do not.

Or should platform_get_irq() return a negative error instead of 0?
If 0 is not a valid interrupt, I think it would be easier to use the
interface if we made it so platform_get_irq() could never return 0,
which I think would also fit the interface documentation better:

 * Return: IRQ number on success, negative error number on failure.

Bjorn