The
pci_intr functions exist to allow device drivers machine-independent access to PCI bus interrupts. The functions described in this page are typically declared in a port's
<machine/pci_machdep.h> header file; however, drivers should generally include
<dev/pci/pcivar.h> to get other PCI-specific declarations as well.
Each driver has an
attach() function which has a bus-specific
attach_args structure. Each driver for a PCI device is passed a pointer to an object of type
struct pci_attach_args which contains, among other things, information about the location of the device in the PCI bus topology sufficient to allow interrupts from the device to be handled.
If a driver wishes to establish an interrupt handler for the device, it should pass the
struct pci_attach_args * to the
pci_intr_map() function, which returns zero on success, and nonzero on failure. The function sets the
pci_intr_handle_t pointed at by its second argument to a machine-dependent value which identifies a particular interrupt source.
If the driver wishes to refer to the interrupt source in an attach or error message, it should use the value returned by
pci_intr_string().
Subsequently, when the driver is prepared to receive interrupts, it should call
pci_intr_establish() to actually establish the handler; when the device interrupts,
intrhand will be called with a single argument
intrarg, and will run at the interrupt priority level
ipl.
The return value of
pci_intr_establish() may be saved and passed to
pci_intr_disestablish() to disable the interrupt handler when the driver is no longer interested in interrupts from the device.
PORTING
A port's implementation of
pci_intr_map() may use the following members of
struct pci_attach_args to determine how the device's interrupts are routed.
pci_chipset_tag_t pa_pc;
pcitag_t pa_tag;
pcitag_t pa_intrtag; /* intr. appears to come from here */
pci_intr_pin_t pa_intrpin; /* intr. appears on this pin */
pci_intr_line_t pa_intrline; /* intr. routing information */
pci_intr_pin_t pa_rawintrpin; /* unswizzled pin */
PCI-PCI bridges swizzle (permute) interrupt wiring. Depending on implementation details, it may be more convenient to use either original or the swizzled interrupt parameters. The original device tag and interrupt pin can be found in
pa_tag and
pa_rawintrpin respectively, while the swizzled tag and pin can be found in
pa_intrtag and
pa_intrpin.
When a device is attached to a primary bus, both pairs of fields contain the same values. When a device is found behind one or more pci-pci bridges,
pa_intrpin contains the “swizzled” interrupt pin number, while
pa_rawintrpin contains the original interrupt pin;
pa_tag contains the PCI tag of the device itself, and
pa_intrtag contains the PCI tag of the uppermost bridge device.