linux-kernel - Re: [PATCH] of_pci_irq: Silence bogus "of_irq_parse

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Date:	Fri, 04 Sep 2015 18:40:28 -0700
From:	David Daney <ddaney.cavm@...il.com>
To:	frowand.list@...il.com
CC:	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH] of_pci_irq: Silence bogus "of_irq_parse_pci() failed
 ..." messages.

On 09/04/2015 06:14 PM, Frank Rowand wrote:
> On 9/4/2015 12:12 PM, David Daney wrote:
>> From: David Daney <david.daney@...ium.com>
>>
>> It is perfectly legitimate for a PCI device to have an
>> PCI_INTERRUPT_PIN value of zero.  This happens if the device doesn't
>> use interrupts, or on PCIe devices, where only MSI/MSI-X are
>> supported.
>>
>> Silence the annoying "of_irq_parse_pci() failed with rc=-19" error
>> messages by making them conditional on !-ENODEV (which can only be
>> produced in the PCI_INTERRUPT_PIN == 0 case).
>>
>> Signed-off-by: David Daney <david.daney@...ium.com>
>> ---
>>   drivers/of/of_pci_irq.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/of/of_pci_irq.c b/drivers/of/of_pci_irq.c
>> index 1710d9d..33d242a 100644
>> --- a/drivers/of/of_pci_irq.c
>> +++ b/drivers/of/of_pci_irq.c
>> @@ -106,7 +106,9 @@ int of_irq_parse_and_map_pci(const struct pci_dev *dev, u8 slot, u8 pin)
>>
>>   	ret = of_irq_parse_pci(dev, &oirq);
>>   	if (ret) {
>> -		dev_err(&dev->dev, "of_irq_parse_pci() failed with rc=%d\n", ret);
>> +		if (ret != -ENODEV)
>> +			dev_err(&dev->dev,
>> +				"of_irq_parse_pci() failed with rc=%d\n", ret);
>>   		return 0; /* Proper return code 0 == NO_IRQ */
>>   	}
>>
>>
>
> It is not safe to assume that the functions that of_irq_parse_pci() calls
> will never be modified to return -ENODEV, thus resulting in of_irq_parse_pci()
> returning -ENODEV for a reason other than PCI_INTERRUPT_PIN == 0.
>

Since the current implementation *only ever* returns -ENODEV for 
PCI_INTERRUPT_PIN == 0, we could just document that behavior, and not 
hack up the APIs by adding a second return channel from the function.

The additional change on top of my patch would be to add a comment 
describing this behavior.

David Daney.



> A more robust solution would be something like:
>
>
> (1) Change of_irq_parse_pci() to _of_irq_parse_pci(), adding an argument and
> use it to report the case of PCI_INTERRUPT_PIN == 0.
>
> static int _of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq, int *no_pin)
> {
>
> ...
> 	*no_pin = 0;
> ...
> 	/* No pin, exit */
> 	if (pin == 0) {
> 		*no_pin = 1;
> 		return -ENODEV;
> 	}
> ...
>
>
> int of_irq_parse_pci(const struct pci_dev *pdev, struct of_phandle_args *out_irq)
> {
> 	int no_pin;
> 	return _of_irq_parse_pci(pdev, out_irq, &no_pin)
> }
>
>
> (2) Then the fix to of_irq_parse_and_map_pci() would be:
>
>    +     int no_pin;
>>   	ret = of_irq_parse_pci(dev, &oirq, &no_pin);
>>   	if (ret) {
>> -		dev_err(&dev->dev, "of_irq_parse_pci() failed with rc=%d\n", ret);
>> +		if (!no_pin)
>> +			dev_err(&dev->dev,
>> +				"of_irq_parse_pci() failed with rc=%d\n", ret);
>>   		return 0; /* Proper return code 0 == NO_IRQ */
>>   	}
>
>
> I'm not sure I like my solution, there might be a better way.
>
> I also noticed another bug while looking at of_irq_parse_pci().  It returns
> the non-zero return value from pci_read_config_byte().  But that value is
> one of the PCI function error values from include/linux/pci.h, such as:
>
>     #define PCIBIOS_BAD_REGISTER_NUMBER     0x87
>
> instead of a negative errno.
>
>
> -Frank
>

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