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

Bjorn Helgaas
2008-12-11T18:24:29Z

On Thursday 11 December 2008 11:14:55 am David Howells wrote:
> Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
>
> > +/**
> > + * 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, section 9.1, requires INTx swizzling
> > + * for devices behind bridges on add-in cards. This performs the swizzle
> > + * for one level of bridge.
> > + */
>
> That's okay. It might be better to put the what before the why, though:
>
> * Perform INTx swizzling for a device behind one level of bridge. This is
> * required by section 9.1 of the PCI-to-PCI bridge specification for devices
> * behind bridges on add-in cards.

That *is* much better. Thanks for the wordsmithing.

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 | 16 +++++++++++++++-
include/linux/pci.h | 1 +
2 files changed, 16 insertions(+), 1 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 46f6821..388a32a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -1337,6 +1337,20 @@ 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)
+ *
+ * Perform INTx swizzling for a device behind one level of bridge. This is
+ * required by section 9.1 of the PCI-to-PCI bridge specification for devices
+ * behind bridges on add-in cards.
+ */
+u8 pci_swizzle_interrupt_pin(struct pci_dev *dev, u8 pin)
+{
+ return (((pin - 1) + PCI_SLOT(dev->devfn)) % 4) + 1;
+}
+
int
pci_get_interrupt_pin(struct pci_dev *dev, struct pci_dev **bridge)
{
@@ -1347,7 +1361,7 @@ 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);