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
18void 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}