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

[David Daney]

On 01/22/2016 09:53 AM, Bjorn Helgaas wrote:
> 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@xxxxxxxxxxxxxx> 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"?

In many (most) cases, zero indicates no irq.




> 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