v4.19.13 snapshot.
diff --git a/drivers/pci/setup-irq.c b/drivers/pci/setup-irq.c
new file mode 100644
index 0000000..7129494
--- /dev/null
+++ b/drivers/pci/setup-irq.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support routines for initializing a PCI subsystem
+ *
+ * Extruded from code written by
+ * Dave Rusling (david.rusling@reo.mts.dec.com)
+ * David Mosberger (davidm@cs.arizona.edu)
+ * David Miller (davem@redhat.com)
+ */
+
+
+#include <linux/kernel.h>
+#include <linux/pci.h>
+#include <linux/errno.h>
+#include <linux/ioport.h>
+#include <linux/cache.h>
+#include "pci.h"
+
+void pci_assign_irq(struct pci_dev *dev)
+{
+ u8 pin;
+ u8 slot = -1;
+ int irq = 0;
+ struct pci_host_bridge *hbrg = pci_find_host_bridge(dev->bus);
+
+ if (!(hbrg->map_irq)) {
+ pci_dbg(dev, "runtime IRQ mapping not provided by arch\n");
+ return;
+ }
+
+ /* If this device is not on the primary bus, we need to figure out
+ which interrupt pin it will come in on. We know which slot it
+ will come in on 'cos that slot is where the bridge is. Each
+ time the interrupt line passes through a PCI-PCI bridge we must
+ apply the swizzle function. */
+
+ pci_read_config_byte(dev, PCI_INTERRUPT_PIN, &pin);
+ /* Cope with illegal. */
+ if (pin > 4)
+ pin = 1;
+
+ if (pin) {
+ /* Follow the chain of bridges, swizzling as we go. */
+ if (hbrg->swizzle_irq)
+ slot = (*(hbrg->swizzle_irq))(dev, &pin);
+
+ /*
+ * If a swizzling function is not used map_irq must
+ * ignore slot
+ */
+ irq = (*(hbrg->map_irq))(dev, slot, pin);
+ if (irq == -1)
+ irq = 0;
+ }
+ dev->irq = irq;
+
+ pci_dbg(dev, "assign IRQ: got %d\n", dev->irq);
+
+ /* Always tell the device, so the driver knows what is
+ the real IRQ to use; the device does not use it. */
+ pci_write_config_byte(dev, PCI_INTERRUPT_LINE, irq);
+}