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DESCRIPTION

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.

pci_msi_count() returns the max number of the device's MSI. If the device can not use MSI, pci_msi_count() returns zero. pci_msix_count() works in the same manner for MSI-X.

If a driver wishes to establish an MSI handler for the device, it should pass the struct pci_attach_args * and count pci_msi_alloc() or pci_msi_alloc_exact() functions, which return zero on success, and nonzero on failure. When the functions are successful, they return the pointer to the allocated handle array in pihs whose size is count or less. The difference between pci_msi_alloc() and pci_msi_alloc_exact() is whether count can be decremented or not. pci_msi_alloc() can decrement count, and which is similar to FreeBSD's pci_alloc_msi(). In contrast, pci_msi_alloc_exact() can not decrement count.

If the driver wishes to refer to the MSI source in an attach or error message, it should use the value returned by pci_intr_string() the same as INTx. The buffer passed to pci_intr_string() should be at least PCI_INTRSTR_LEN bytes long.

Subsequently, when the driver is prepared to receive MSIs, it should call pci_intr_establish() the same as INTx 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 the same as INTx when the driver is no longer interested in MSIs from the device. After that, the driver should also call pci_intr_release() to free resources about MSI as well as INTx and MSI-X. If pih is NULL, pci_intr_release() does nothing.

If a driver wishes to establish an MSI-X handler for the device, it is almost the same as MSI. The only differences is pci_msix_alloc_map(). This function can assign separate handlers for each MSI-X table entry. I.e., if the driver wants to assign the handlers in the following way:

	msix_handler0 => MSI-X table index: 4
	msix_handler1 => MSI-X table index: 5
	msix_handler2 => MSI-X table index: 0

	table_indexes[0] = 4;
	table_indexes[1] = 5;
	table_indexes[2] = 0;

If the driver wants to fall back to INTx, the driver should use pci_intx_alloc() and pci_intr_release() instead of pci_intr_map() to resolve contradiction of the interrupt handler ownership. I.e., pci_intr_map() does not have the ownership (the function just calculates value), in contrast, pci_msi_alloc() and pci_msix_alloc() have (the functions allocate memory for interrupt handlers).

pci_intr_alloc() is wrapper function which select and automatically fallback allocation functions according to the argument counts. The elements of counts array means each required interrupt count for INTx, MSI, and MSI-X. The index count of counts must be PCI_INTR_TYPE_SIZE. max_type must be PCI_INTR_TYPE_MSIX, PCI_INTR_TYPE_MSI, or PCI_INTR_TYPE_INTX. The parameter does not mean array index counts of counts. The parameter means the interrupt type which pci_intr_alloc() tries to allocate first. I.e., if the driver wants to allocate interrupts in the following way:

	5 MSI-X
	1 MSI (if MSI-X allocation failed)
	INTx (if MSI allocation failed either)

	int counts[PCI_INTR_TYPE_SIZE];
	counts[PCI_INTR_TYPE_MSIX] = 5;
	counts[PCI_INTR_TYPE_MSI] = 1;
	counts[PCI_INTR_TYPE_INTX] = 1;
	error = pci_intr_alloc(pa, ihps, counts,
			       PCI_INTR_TYPE_MSIX);

	hardware max number MSI-X
	1 MSI (if MSI-X allocation failed)

	int counts[PCI_INTR_TYPE_SIZE];
	counts[PCI_INTR_TYPE_MSIX] = -1; /* -1 means max */
	counts[PCI_INTR_TYPE_MSI] = 1;
	counts[PCI_INTR_TYPE_INTX] = 0; /* 0 means not use */
	error = pci_intr_alloc(pa, ihps, counts,
			       PCI_INTR_TYPE_MSIX);

	3 MSI
	INTx (if MSI allocation failed)

	int counts[PCI_INTR_TYPE_SIZE];
	counts[PCI_INTR_TYPE_MSIX] = 0; /* 0 means not use */
	counts[PCI_INTR_TYPE_MSI] = 3;
	counts[PCI_INTR_TYPE_INTX] = 1;
	error = pci_intr_alloc(pa, ihps, counts,
			       PCI_INTR_TYPE_MSI);

	1 MSI-X
	1 MSI
	INTx (if MSI/MSI-X allocation failed)

	error = pci_intr_alloc(pa, ihps, NULL, 0);

	counts[PCI_INTR_TYPE_MSIX] == 5
	counts[PCI_INTR_TYPE_MSI] == 0
	counts[PCI_INTR_TYPE_INTX] == 0

pci_intr_type() returns the interrupt type of ih. The return value is PCI_INTR_TYPE_MSIX for MSI-X, PCI_INTR_TYPE_MSI for MSI, and PCI_INTR_TYPE_INTX for others.