original_kernel/drivers/of/of_pci.c

#include <linux/kernel.h>
#include <linux/of.h>
#include <linux/of_pci.h>
#include <asm/prom.h>

static inline int __of_pci_pci_compare(struct device_node *node,
				       unsigned int devfn)
{
	unsigned int size;
	const __be32 *reg = of_get_property(node, "reg", &size);

	if (!reg || size < 5 * sizeof(__be32))
		return 0;
	return ((be32_to_cpup(&reg[0]) >> 8) & 0xff) == devfn;
}

struct device_node *of_pci_find_child_device(struct device_node *parent,
					     unsigned int devfn)
{
	struct device_node *node, *node2;

	for_each_child_of_node(parent, node) {
		if (__of_pci_pci_compare(node, devfn))
			return node;
		/*
		 * Some OFs create a parent node "multifunc-device" as
		 * a fake root for all functions of a multi-function
		 * device we go down them as well.
		 */
		if (!strcmp(node->name, "multifunc-device")) {
			for_each_child_of_node(node, node2) {
				if (__of_pci_pci_compare(node2, devfn)) {
					of_node_put(node);
					return node2;
				}
			}
		}
	}
	return NULL;
}
EXPORT_SYMBOL_GPL(of_pci_find_child_device);