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