[+cc another Marc]
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. 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].
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
