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

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Date:	Sun, 06 Sep 2015 20:50:51 -0700
From:	Frank Rowand <frowand.list@...il.com>
To:	frowand.list@...il.com
CC:	Rob Herring <robherring2@...il.com>,
	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 7:16 PM, Frank Rowand wrote:
> 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.

And this time I replied too quickly, not really thinking through my comment.
There are several error return points in of_irq_parse_pci(), so moving the
error message into of_irq_parse_pci() is not the answer.


>>> 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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