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

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Date:	Fri, 04 Sep 2015 19:38:29 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	David Daney <ddaney.cavm@...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 9/4/2015 6:40 PM, David Daney wrote:
> 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.

And for each function that of_irq_parse_pci() calls and returns status from the
function call you would need to document that behavior, and so on recursively.

For example, you would need to document of_irq_parse_one().  And that returns status
from more function calls, so you would need to document of_irq_parse_oldworld(),
of_parse_phandle_with_args(), of_irq_parse_raw(), and then anything they call.
> 
> The additional change on top of my patch would be to add a comment describing this behavior.
> 
> David Daney.

< snip >

-Frank

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