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    SubjectRe: [PATCH] of_pci_irq: Silence bogus "of_irq_parse_pci() failed ..." messages.
    On Fri, Sep 4, 2015 at 8:14 PM, Frank Rowand <frowand.list@gmail.com> wrote:
    > On 9/4/2015 12:12 PM, David Daney wrote:
    >> From: David Daney <david.daney@cavium.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@cavium.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:
    >
    >
    > (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 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 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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