Re: [PATCH v2] pci: fix unavailable irq number 255 reported by BIOS

[Chen Fan]

On 01/26/2016 04:26 PM, Thomas Gleixner wrote:
> 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?
quoting the spec document:
"For x86 based PCs, the values in this register correspond to IRQ 
numbers (0-15) of the standard dual
8259 configuration. The value 255 is defined as meaning "unknown" or "no 
connection" to the interrupt
controller. Values between 15 and 254 are reserved."

> > > +		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.
yes, this is what I thought in previous email, I has asked that
whether we can use a broken_irq flag in pci_dev to mark the device irq 
if invalid.
and then if the device broken_irq set, we could directly skip call the 
request_irq.
maybe we can set the broken_irq in pci_read_irq if the irq is 0xff.

Thanks,
Chen

> > > +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
>
>
>
> .