On Mon, 25 Jan 2016, Bjorn Helgaas wrote:
> On Mon, Jan 25, 2016 at 02:59:38PM +0800, Chen Fan wrote:
> > i801_smbus 0000:00:1f.3: PCI INT C: no GSI
> > i801_smbus 0000:00:1f.3: Failed to allocate irq 255: -16
> > i801_smbus: probe of 0000:00:1f.3 failed with error -16
The current code does not not fail when the interrupt request fails. It
reports it and clears the IRQ feature flag.
> > @@ -436,7 +437,15 @@ int acpi_pci_irq_enable(struct pci_dev *dev)
> > * driver reported one, then use it. Exit in any case.
> > */
> > if (gsi < 0) {
> > - if (acpi_isa_register_gsi(dev))
> > +#ifdef CONFIG_X86
> > + /*
> > + * The Interrupt Line value of 0xff is defined to mean "unknown"
> > + * or "no connection" (PCI 3.0, Section 6.2.4, footnote on page
> > + * 223), using ~0U as invalid IRQ.
> > + */
And why would this be x86 specific? PCI3.0 is architecture independent, right?
> > + dev->irq = (dev->irq == 0xff) ? IRQ_INVALID : dev->irq;
>
> It's much simpler and clearer to write:
>
> if (dev->irq == 0xff)
> dev->irq = IRQ_INVALID;
I do not understand that IRQ_INVALID business at all.
> > +#endif
> > + if (!irq_is_valid(dev->irq) || acpi_isa_register_gsi(dev))
> > dev_warn(&dev->dev, "PCI INT %c: no GSI\n",
> > pin_name(pin));
> >
The existing code already drops into this place because
acpi_isa_register_gsi() fails.
> > i801_smbus 0000:00:1f.3: PCI INT C: no GSI
What extra value does that !irq_is_valid() provide?
And how does setting dev->irq to ~0U prevent that request_irq() is called in
the i801 device driver? Not at all, AFAICT. It will just fail with a different
error.
So the whole 'fix' relies on the fact that irq ~0U does not exist (at least
not today) and therefor the false sharing with some other driver using irq 255
will not happen.
Relying on undocumented behaviour is not a fix, that's voodoo programming.
The proper solution here is to flag that this device does not have an
interrupt connected and act accordingly in the device driver, i.e. do not call
request_irq() in the first place.
> > +static inline bool irq_is_valid(unsigned int irq)
> > +{
> > +#ifdef CONFIG_X86
> > + if (irq == IRQ_INVALID)
> > + return false;
> > +#endif
> > + return true;
> > +}
>
> I don't like the x86 ifdef. I'd prefer:
>
> static inline bool irq_valid(unsigned int irq)
> {
> if (irq < NR_IRQS)
> return true;
> return false;
> }
>
> This could be used in many of the places that currently use NR_IRQS.
No. NR_IRQS cannot be used at all if sparse irqs are enabled. Nothing in any
generic code is supposed to rely on NR_IRQS.
Thanks,
tglx
