Re: [PATCH kernel] powerpc/pci: Fix broken INTx configuration via OF

On Thu, Feb 08, 2018 at 01:20:04PM -0600, Bjorn Helgaas wrote:

[+cc linux-pci]

The original commit was merged via PCI, and I think it's a good idea
to merge fixes to it the same way.  I'll try to merge this in time for
v4.16-rc1.

On Wed, Feb 7, 2018 at 11:33 PM, Alexey Kardashevskiy [off-list ref] wrote:

quoted

Commit 59f47eff03a0 ("powerpc/pci: Use of_irq_parse_and_map_pci() helper")
correctly states that of_irq_parse_and_map_pci() does the same thing as
of_irq_parse_pci() does as it simply calls
of_irq_parse_pci() and irq_create_of_mapping().

However of_irq_parse_and_map_pci() not only returns 0 for success and
negative value for an error but also a positive virq value from
irq_create_of_mapping() which the mentioned commit ignores and
INTx config fails.

This fixes the of_irq_parse_and_map_pci() return value handling.

Fixes: 59f47eff03a0 "powerpc/pci: Use of_irq_parse_and_map_pci() helper"
Signed-off-by: Alexey Kardashevskiy <redacted>
---

Found it on POWER9 + powernv system - almost all devices suddenly lost
INTx support.
---
 arch/powerpc/kernel/pci-common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
index ae2ede4..acbb44f2 100644
--- a/arch/powerpc/kernel/pci-common.c
+++ b/arch/powerpc/kernel/pci-common.c

@@ -370,7 +370,8 @@ static int pci_read_irq_line(struct pci_dev *pci_dev)
        memset(&oirq, 0xff, sizeof(oirq));
 #endif
        /* Try to get a mapping from the device-tree */
-       if (!of_irq_parse_and_map_pci(pci_dev, 0, 0)) {
+       virq = of_irq_parse_and_map_pci(pci_dev, 0, 0);
+       if (virq <= 0) {

I don't understand how this fix works.  We used to check the result of
of_irq_parse_and_map_pci() and entered the block if it was zero.

Now you enter the block if it is zero or less than zero, but:

  static int pci_read_irq_line(...)
  {
    unsigned int virq = 0;     /* unnecessarily initialized, BTW */

    virq = of_irq_parse_and_map_pci(pci_dev, 0, 0);
    if (virq <= 0) {
      ...

virq is unsigned, so "virq < 0" can never be true.  So how does this
change anything?

Bjorn