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

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Jan 21, 2016 at 11:58:26PM +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 21, 2016 at 3:41 PM, Cao jin <caoj.fnst@cn.fujitsu.com> wrote:
> > Hi,
> >
> >     IMHO, I think maybe modification on i801_smbus driver is easier.
> >
> >     Because when i801_smbus request_irq using pci_dev->irq, this
> > pci_dev->irq seems still holds the value read from register(
> > pci_setup_device->pci_read_irq), if the value is 255, it is invalid in
> > register,
> 
> Right.
> 
> Which is why the PCI core should not leak it into the driver's ->probe callback.

Is there a reserved IRQ value we could use to mean "invalid"?

I guess we have NR_IRQS as a ceiling, so the range of valid IRQs would be
[0 .. NR_IRQS - 1].  It looks like irq_desc() and a few drivers already
rely on NR_IRQS being the bound:

  lpc32xx_kscan_probe
  lpc32xx_nand_probe
  pcmcia_setup_isa_irq
  lpc32xx_rtc_probe
  apbuart_verify_port
  ar933x_uart_verify_port
  lqasc_verify_port

So I guess we could use ~0 as "invalid IRQ", and maybe the PCI core could
set dev->irq to ~0 in these cases, and drivers like i801_smbus could check
for that.  Maybe a wrapper like irq_valid() would be useful.

Bjorn