Date:	Tue, 26 Jan 2016 17:45:46 +0800
From:	Chen Fan <chen.fan.fnst@...fujitsu.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <helgaas@...nel.org>
CC:	<linux-acpi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<rjw@...ysocki.net>, <lenb@...nel.org>,
	<izumi.taku@...fujitsu.com>, <wency@...fujitsu.com>,
	<caoj.fnst@...fujitsu.com>, <ddaney.cavm@...il.com>,
	<okaya@...eaurora.org>, <bhelgaas@...gle.com>,
	<jiang.liu@...ux.intel.com>, <linux-pci@...r.kernel.org>
Subject: Re: [PATCH v2] pci: fix unavailable irq number 255 reported by BIOS


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
>
>
>
> .
>

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