[PATCH 05/12] PCI: add pci_swizzle_interrupt_pin()

[Bjorn Helgaas <bjorn.helgaas@hp.com>]

This patch adds pci_swizzle_interrupt_pin(), which implements the
INTx swizzling algorithm specified in Table 9-1 of the "PCI-to-PCI
Bridge Architecture Specification," revision 1.2.

There are many architecture-specific implementations of this
swizzle that can be replaced by this common one.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
---
 drivers/pci/pci.c   |    8 +++++++-
 include/linux/pci.h |    1 +
 2 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 46f6821..5a882cc 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1337,6 +1337,12 @@ void pci_enable_ari(struct pci_dev *dev)
 	bridge->ari_enabled = 1;
 }
 
+u8 pci_swizzle_interrupt_pin(struct pci_dev *dev, u8 pin)
+{
+	/* This implements Table 9-1 of the PCI-to-PCI bridge spec */
+	return (((pin - 1) + PCI_SLOT(dev->devfn)) % 4) + 1;
+}
+
 int
 pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge)
 {
@@ -1347,7 +1353,7 @@ pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge)
 		return -1;
 
 	while (dev->bus->self) {
-		pin = (((pin - 1) + PCI_SLOT(dev->devfn)) % 4) + 1;
+		pin = pci_swizzle_interrupt_pin(dev, pin);
 		dev = dev->bus->self;
 	}
 	*bridge = dev;
diff --git a/include/linux/pci.h b/include/linux/pci.h
index feb4657..4be596f 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -527,6 +527,7 @@ int __must_check pci_bus_add_device(struct pci_dev *dev);
 void pci_read_bridge_bases(struct pci_bus *child);
 struct resource *pci_find_parent_resource(const struct pci_dev *dev,
 					  struct resource *res);
+u8 pci_swizzle_interrupt_pin(struct pci_dev *dev, u8 pin);
 int pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge);
 extern struct pci_dev *pci_dev_get(struct pci_dev *dev);
 extern void pci_dev_put(struct pci_dev *dev);