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

Bjorn Helgaas
2008-12-11T16:48:19Z

On Thursday 11 December 2008 08:00:24 am David Howells wrote:
> Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
>
> >
> > +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;
> > +}
> > +
>
> Can you please add a banner comment to this function that gives at least a
> quick description of what this function is meant to do? Feel free to use
> kerneldoc.

I'm not really a fan of comments that are bigger than the code
and add little or no information, but if you like the following
better, use it instead :-)

PCI: add pci_swizzle_interrupt_pin()

From: 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 | 17 ++++++++++++++++-
include/linux/pci.h | 1 +
2 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 46f6821..c14a6b6 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1337,6 +1337,21 @@ void pci_enable_ari(struct pci_dev *dev)
bridge->ari_enabled = 1;
}

+/**
+ * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
+ * @dev: the PCI device
+ * @pin: the INTx pin (1=INTA, 2=INTB, 3=INTD, 4=INTD)
+ *
+ * The PCI-to-PCI bridge specification requires INTx swizzling for
+ * devices behind bridges on add-in cards. This performs the swizzle
+ * for one level of bridge.
+ */
+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 +1362,7 @@ 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);