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

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Date:	Fri, 04 Sep 2015 18:14:11 -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 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.

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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