From: Marc Gonzalez <marc.w.gonzalez@free.fr>
To: Bjorn Helgaas <helgaas@kernel.org>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Marc Zyngier <maz@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Cc: Ryder Lee <ryder.lee@mediatek.com>,
Karthikeyan Mitran <m.karthikeyan@mobiveil.co.in>,
linux-pci@vger.kernel.org,
Linus Walleij <linus.walleij@linaro.org>,
Aman Sharma <amanharitsh123@gmail.com>,
linux-kernel@vger.kernel.org, Mans Rullgard <mans@mansr.com>,
linux-mediatek@lists.infradead.org,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
Matthias Brugger <matthias.bgg@gmail.com>,
Hou Zhiqiang <Zhiqiang.Hou@nxp.com>,
linux-arm-kernel@lists.infradead.org,
Andrew Murray <amurray@thegoodpenguin.co.uk>
Subject: Re: [PATCH 4/5] pci: handled return value of platform_get_irq correctly
Date: Thu, 12 Mar 2020 16:53:12 +0100 [thread overview]
Message-ID: <b145096e-8628-c551-4846-2eb5ce0334f6@free.fr> (raw)
In-Reply-To: <20200312141102.GA93224@google.com>
On 12/03/2020 15:11, Bjorn Helgaas wrote:
> [+cc another Marc]
Doh! I should indeed have CCed maz and tglx.
> On Thu, Mar 12, 2020 at 10:53:06AM +0100, Marc Gonzalez wrote:
>
>> On 11/03/2020 20:19, Aman Sharma wrote:
>>
>>> diff --git a/drivers/pci/controller/pcie-tango.c b/drivers/pci/controller/pcie-tango.c
>>> index 21a208da3f59..18c2c4313eb5 100644
>>> --- a/drivers/pci/controller/pcie-tango.c
>>> +++ b/drivers/pci/controller/pcie-tango.c
>>> @@ -273,9 +273,9 @@ static int tango_pcie_probe(struct platform_device *pdev)
>>> writel_relaxed(0, pcie->base + SMP8759_ENABLE + offset);
>>>
>>> virq = platform_get_irq(pdev, 1);
>>> - if (virq <= 0) {
>>> + if (virq < 0) {
>>> dev_err(dev, "Failed to map IRQ\n");
>>> - return -ENXIO;
>>> + return virq;
>>> }
>>>
>>> irq_dom = irq_domain_create_linear(fwnode, MSI_MAX, &dom_ops, pcie);
>>
>> Weee, here we go again :-)
>>
>> https://patchwork.kernel.org/patch/11066455/
>> https://patchwork.kernel.org/patch/10006651/
>>
>> 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;
>
> I still think what I said in 2019 is the right approach. I do see
> your comment in 10006651 about this pattern:
>
> if (virq <= 0)
> return virq ? : -ENODEV;
>
> but IMHO it's too complicated for general use. Admittedly, it's not
> *very* complicated, but it's a relatively unusual C idiom and I
> stumble over it every time I see it.
FTR, omitting the middle operand is a GNU extension.
https://gcc.gnu.org/onlinedocs/gcc/Conditionals.html
The valid C idiom would be virq ? virq : -ENODEV
> If 0 is a special case I think
> it should be mapped to a negative error in arch-specific code, which I
> think is what Linus T suggested in [1].
Lorenzo, being both PCI maintainer and ARM employee should be in a
good position to change the arch-specific code for arm and arm64?
> I think there's still a large consensus that "irq < 0" is the error
> case. In the tree today we have about 1400 callers of
> platform_get_irq() and platform_get_irq_byname() [2]. Of those,
> almost 900 check for "irq < 0" [3], while only about 150 check for
> "irq <= 0" [4] and about 15 use some variant of a "irq ? : -ENODEV"
> pattern.
>
> The bottom line is that in drivers/pci, I'd like to see either a
> single style or a compelling argument for why some checks should be
> "irq < 0" and others should be "irq <= 0".
>
> [1] https://yarchive.net/comp/linux/zero.html
> [2] $ git grep "=.*platform_get_irq" | wc -l
> 1422
> [3] $ git grep -A4 "=.*platform_get_irq" | grep "<\s*0" | wc -l
> 894
> [4] $ git grep -A4 "=.*platform_get_irq" | grep "<=\s*0" | wc -l
> 151
> [5] $ git grep -A4 "=.*platform_get_irq" | grep "return.*?.*:.*;" | wc -l
> 15
Interesting stats, thanks.
Regards.
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next prev parent reply other threads:[~2020-03-12 15:53 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-11 19:19 [PATCH 0/5] Handled return value of platform_get_irq correctly Aman Sharma
2020-03-11 19:19 ` [PATCH 1/5] pci: handled " Aman Sharma
2020-03-12 14:07 ` Linus Walleij
2020-03-12 19:02 ` Bjorn Helgaas
2020-03-12 22:45 ` Linus Walleij
2020-03-11 19:19 ` [PATCH 2/5] pci: added check for return value of platform_get_irq Aman Sharma
2020-03-11 19:19 ` [PATCH 3/5] pci: handled return value of platform_get_irq correctly Aman Sharma
2020-03-11 19:19 ` [PATCH 4/5] " Aman Sharma
2020-03-12 9:53 ` Marc Gonzalez
2020-03-12 14:11 ` Bjorn Helgaas
2020-03-12 15:53 ` Marc Gonzalez [this message]
2020-03-13 21:05 ` Thomas Gleixner
2020-03-13 21:56 ` Bjorn Helgaas
2020-03-17 22:03 ` Bjorn Helgaas
2020-03-18 13:42 ` Thomas Gleixner
2020-03-18 22:22 ` Bjorn Helgaas
2020-03-19 8:47 ` Thomas Gleixner
2020-03-19 21:35 ` Bjorn Helgaas
2020-03-11 19:19 ` [PATCH 5/5] pci: added check for return value of platform_get_irq Aman Sharma
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