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

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Date:	Fri, 22 Jan 2016 11:23:34 -0800
From:	David Daney <ddaney.cavm@...il.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
CC:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Cao jin <caoj.fnst@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Chen Fan <chen.fan.fnst@...fujitsu.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>, izumi.taku@...fujitsu.com,
	wency@...fujitsu.com, Bjorn Helgaas <bhelgaas@...gle.com>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Jiang Liu <jiang.liu@...ux.intel.com>
Subject: Re: [PATCH] pci: fix unavailable irq number 255 reported by BIOS

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@...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"?

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
>
>