1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Support routines for initializing a PCI subsystem
4 *
5 * Extruded from code written by
6 * Dave Rusling (david.rusling@reo.mts.dec.com)
7 * David Mosberger (davidm@cs.arizona.edu)
8 * David Miller (davem@redhat.com)
9 */
10
11 #include <linux/kernel.h>
12 #include <linux/pci.h>
13 #include <linux/errno.h>
14 #include <linux/ioport.h>
15 #include <linux/cache.h>
16 #include "pci.h"
17
pci_assign_irq(struct pci_dev * dev)18 void pci_assign_irq(struct pci_dev *dev)
19 {
20 u8 pin;
21 u8 slot = -1;
22 int irq = 0;
23 struct pci_host_bridge *hbrg = pci_find_host_bridge(dev->bus);
24
25 if (!(hbrg->map_irq)) {
26 pci_dbg(dev, "runtime IRQ mapping not provided by arch\n");
27 return;
28 }
29
30 /*
31 * If this device is not on the primary bus, we need to figure out
32 * which interrupt pin it will come in on. We know which slot it
33 * will come in on because that slot is where the bridge is. Each
34 * time the interrupt line passes through a PCI-PCI bridge we must
35 * apply the swizzle function.
36 */
37 pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin);
38 /* Cope with illegal. */
39 if (pin > 4)
40 pin = 1;
41
42 if (pin) {
43 /* Follow the chain of bridges, swizzling as we go. */
44 if (hbrg->swizzle_irq)
45 slot = (*(hbrg->swizzle_irq))(dev, &pin);
46
47 /*
48 * If a swizzling function is not used, map_irq() must
49 * ignore slot.
50 */
51 irq = (*(hbrg->map_irq))(dev, slot, pin);
52 if (irq == -1)
53 irq = 0;
54 }
55 dev->irq = irq;
56
57 pci_dbg(dev, "assign IRQ: got %d\n", dev->irq);
58
59 /*
60 * Always tell the device, so the driver knows what is the real IRQ
61 * to use; the device does not use it.
62 */
63 pci_write_config_byte(dev, PCI_INTERRUPT_LINE, irq);
64 }
65