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

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Date:	Sun, 06 Sep 2015 19:16:29 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	Rob Herring <robherring2@...il.com>
CC:	David Daney <ddaney.cavm@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...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 9/6/2015 1:46 PM, Rob Herring wrote:
> On Fri, Sep 4, 2015 at 8:14 PM, Frank Rowand <frowand.list@...il.com> 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.
> 
> Yes, but we're talking about a print statement.
> 
>>
>> A more robust solution would be something like:

< snip my bad solution >

>> I'm not sure I like my solution, there might be a better way.
> 
> I don't like it. That's way too complex for just silencing an
> erroneous error message.
> 
> Perhaps just move the error message into of_irq_parse_pci and then you
> can control the print more easily. Or just change to dev_dbg would be
> okay by me.

I knew I was making it way too hard.  Yes, just move the error message
to of_irq_parse_pci(), where the "/* No pin, exit */" test occurs.

 
>> 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.
> 
> I was puzzled by why this is not standard error codes a while back. My
> best guess is that that there is some legacy here. Changing error
> values on widely used functions is impossible to audit. NO_IRQ being 0
> or -1 is one such case.
> 
> Rob
> 

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