drivers/pci/bus.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * From setup-res.c, by:
  *	Dave Rusling (david.rusling@reo.mts.dec.com)
  *	David Mosberger (davidm@cs.arizona.edu)
  *	David Miller (davem@redhat.com)
  *	Ivan Kokshaysky (ink@jurassic.park.msu.ru)
  */
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/pci.h>
 #include <linux/errno.h>
 #include <linux/ioport.h>
 #include <linux/proc_fs.h>
 #include <linux/slab.h>

 #include "pci.h"

 void pci_add_resource_offset(struct list_head *resources, struct resource *res,
 			     resource_size_t offset)
 {
 	struct resource_entry *entry;

 	entry = resource_list_create_entry(res, 0);
 	if (!entry) {
 		pr_err("PCI: can't add host bridge window %pR\n", res);
 		return;
 	}

 	entry->offset = offset;
 	resource_list_add_tail(entry, resources);
 }
 EXPORT_SYMBOL(pci_add_resource_offset);

 void pci_add_resource(struct list_head *resources, struct resource *res)
 {
 	pci_add_resource_offset(resources, res, 0);
 }
 EXPORT_SYMBOL(pci_add_resource);

 void pci_free_resource_list(struct list_head *resources)
 {
 	resource_list_free(resources);
 }
 EXPORT_SYMBOL(pci_free_resource_list);

 void pci_bus_add_resource(struct pci_bus *bus, struct resource *res,
 			  unsigned int flags)
 {
 	struct pci_bus_resource *bus_res;

 	bus_res = kzalloc(sizeof(struct pci_bus_resource), GFP_KERNEL);
 	if (!bus_res) {
 		dev_err(&bus->dev, "can't add %pR resource\n", res);
 		return;
 	}

 	bus_res->res = res;
 	bus_res->flags = flags;
 	list_add_tail(&bus_res->list, &bus->resources);
 }

 struct resource *pci_bus_resource_n(const struct pci_bus *bus, int n)
 {
 	struct pci_bus_resource *bus_res;

 	if (n < PCI_BRIDGE_RESOURCE_NUM)
 		return bus->resource[n];

 	n -= PCI_BRIDGE_RESOURCE_NUM;
 	list_for_each_entry(bus_res, &bus->resources, list) {
 		if (n-- == 0)
 			return bus_res->res;
 	}
 	return NULL;
 }
 EXPORT_SYMBOL_GPL(pci_bus_resource_n);

 void pci_bus_remove_resource(struct pci_bus *bus, struct resource *res)
 {
 	struct pci_bus_resource *bus_res, *tmp;
 	int i;

 	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {
 		if (bus->resource[i] == res) {
 			bus->resource[i] = NULL;
 			return;
 		}
 	}

 	list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
 		if (bus_res->res == res) {
 			list_del(&bus_res->list);
 			kfree(bus_res);
 			return;
 		}
 	}
 }

 void pci_bus_remove_resources(struct pci_bus *bus)
 {
 	int i;
 	struct pci_bus_resource *bus_res, *tmp;

 	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++)
 		bus->resource[i] = NULL;

 	list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
 		list_del(&bus_res->list);
 		kfree(bus_res);
 	}
 }

 int devm_request_pci_bus_resources(struct device *dev,
 				   struct list_head *resources)
 {
 	struct resource_entry *win;
 	struct resource *parent, *res;
 	int err;

 	resource_list_for_each_entry(win, resources) {
 		res = win->res;
 		switch (resource_type(res)) {
 		case IORESOURCE_IO:
 			parent = &ioport_resource;
 			break;
 		case IORESOURCE_MEM:
 			parent = &iomem_resource;
 			break;
 		default:
 			continue;
 		}

 		err = devm_request_resource(dev, parent, res);
 		if (err)
 			return err;
 	}

 	return 0;
 }
 EXPORT_SYMBOL_GPL(devm_request_pci_bus_resources);

 static struct pci_bus_region pci_32_bit = {0, 0xffffffffULL};
 #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
 static struct pci_bus_region pci_64_bit = {0,
 				(pci_bus_addr_t) 0xffffffffffffffffULL};
 static struct pci_bus_region pci_high = {(pci_bus_addr_t) 0x100000000ULL,
 				(pci_bus_addr_t) 0xffffffffffffffffULL};
 #endif

 /*
  * @res contains CPU addresses.  Clip it so the corresponding bus addresses
  * on @bus are entirely within @region.  This is used to control the bus
  * addresses of resources we allocate, e.g., we may need a resource that
  * can be mapped by a 32-bit BAR.
  */
 static void pci_clip_resource_to_region(struct pci_bus *bus,
 					struct resource *res,
 					struct pci_bus_region *region)
 {
 	struct pci_bus_region r;

 	pcibios_resource_to_bus(bus, &r, res);
 	if (r.start < region->start)
 		r.start = region->start;
 	if (r.end > region->end)
 		r.end = region->end;

 	if (r.end < r.start)
 		res->end = res->start - 1;
 	else
 		pcibios_bus_to_resource(bus, res, &r);
 }

 static int pci_bus_alloc_from_region(struct pci_bus *bus, struct resource *res,
 		resource_size_t size, resource_size_t align,
 		resource_size_t min, unsigned long type_mask,
 		resource_size_t (*alignf)(void *,
 					  const struct resource *,
 					  resource_size_t,
 					  resource_size_t),
 		void *alignf_data,
 		struct pci_bus_region *region)
 {
 	struct resource *r, avail;
 	resource_size_t max;
 	int ret;

 	type_mask |= IORESOURCE_TYPE_BITS;

 	pci_bus_for_each_resource(bus, r) {
 		resource_size_t min_used = min;

 		if (!r)
 			continue;

 		/* type_mask must match */
 		if ((res->flags ^ r->flags) & type_mask)
 			continue;

 		/* We cannot allocate a non-prefetching resource
 		   from a pre-fetching area */
 		if ((r->flags & IORESOURCE_PREFETCH) &&
 		    !(res->flags & IORESOURCE_PREFETCH))
 			continue;

 		avail = *r;
 		pci_clip_resource_to_region(bus, &avail, region);

 		/*
 		 * "min" is typically PCIBIOS_MIN_IO or PCIBIOS_MIN_MEM to
 		 * protect badly documented motherboard resources, but if
 		 * this is an already-configured bridge window, its start
 		 * overrides "min".
 		 */
 		if (avail.start)
 			min_used = avail.start;

 		max = avail.end;

 		/* Don't bother if available space isn't large enough */
 		if (size > max - min_used + 1)
 			continue;

 		/* Ok, try it out.. */
 		ret = allocate_resource(r, res, size, min_used, max,
 					align, alignf, alignf_data);
 		if (ret == 0)
 			return 0;
 	}
 	return -ENOMEM;
 }

 /**
  * pci_bus_alloc_resource - allocate a resource from a parent bus
  * @bus: PCI bus
  * @res: resource to allocate
  * @size: size of resource to allocate
  * @align: alignment of resource to allocate
  * @min: minimum /proc/iomem address to allocate
  * @type_mask: IORESOURCE_* type flags
  * @alignf: resource alignment function
  * @alignf_data: data argument for resource alignment function
  *
  * Given the PCI bus a device resides on, the size, minimum address,
  * alignment and type, try to find an acceptable resource allocation
  * for a specific device resource.
  */
 int pci_bus_alloc_resource(struct pci_bus *bus, struct resource *res,
 		resource_size_t size, resource_size_t align,
 		resource_size_t min, unsigned long type_mask,
 		resource_size_t (*alignf)(void *,
 					  const struct resource *,
 					  resource_size_t,
 					  resource_size_t),
 		void *alignf_data)
 {
 #ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
 	int rc;

 	if (res->flags & IORESOURCE_MEM_64) {
 		rc = pci_bus_alloc_from_region(bus, res, size, align, min,
 					       type_mask, alignf, alignf_data,
 					       &pci_high);
 		if (rc == 0)
 			return 0;

 		return pci_bus_alloc_from_region(bus, res, size, align, min,
 						 type_mask, alignf, alignf_data,
 						 &pci_64_bit);
 	}
 #endif

 	return pci_bus_alloc_from_region(bus, res, size, align, min,
 					 type_mask, alignf, alignf_data,
 					 &pci_32_bit);
 }
 EXPORT_SYMBOL(pci_bus_alloc_resource);

 /*
  * The @idx resource of @dev should be a PCI-PCI bridge window.  If this
  * resource fits inside a window of an upstream bridge, do nothing.  If it
  * overlaps an upstream window but extends outside it, clip the resource so
  * it fits completely inside.
  */
 bool pci_bus_clip_resource(struct pci_dev *dev, int idx)
 {
 	struct pci_bus *bus = dev->bus;
 	struct resource *res = &dev->resource[idx];
 	struct resource orig_res = *res;
 	struct resource *r;

 	pci_bus_for_each_resource(bus, r) {
 		resource_size_t start, end;

 		if (!r)
 			continue;

 		if (resource_type(res) != resource_type(r))
 			continue;

 		start = max(r->start, res->start);
 		end = min(r->end, res->end);

 		if (start > end)
 			continue;	/* no overlap */

 		if (res->start == start && res->end == end)
 			return false;	/* no change */

 		res->start = start;
 		res->end = end;
 		res->flags &= ~IORESOURCE_UNSET;
 		orig_res.flags &= ~IORESOURCE_UNSET;
 		pci_info(dev, "%pR clipped to %pR\n", &orig_res, res);

 		return true;
 	}

 	return false;
 }

 void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }

 void __weak pcibios_bus_add_device(struct pci_dev *pdev) { }

 /**
  * pci_bus_add_device - start driver for a single device
  * @dev: device to add
  *
  * This adds add sysfs entries and start device drivers
  */
 void pci_bus_add_device(struct pci_dev *dev)
 {
 	int retval;

 	/*
 	 * Can not put in pci_device_add yet because resources
 	 * are not assigned yet for some devices.
 	 */
 	pcibios_bus_add_device(dev);
 	pci_fixup_device(pci_fixup_final, dev);
 	pci_create_sysfs_dev_files(dev);
 	pci_proc_attach_device(dev);
 	pci_bridge_d3_update(dev);

 	dev->match_driver = true;
 	retval = device_attach(&dev->dev);
 	if (retval < 0 && retval != -EPROBE_DEFER)
 		pci_warn(dev, "device attach failed (%d)\n", retval);

 	pci_dev_assign_added(dev, true);
 }
 EXPORT_SYMBOL_GPL(pci_bus_add_device);

 /**
  * pci_bus_add_devices - start driver for PCI devices
  * @bus: bus to check for new devices
  *
  * Start driver for PCI devices and add some sysfs entries.
  */
 void pci_bus_add_devices(const struct pci_bus *bus)
 {
 	struct pci_dev *dev;
 	struct pci_bus *child;

 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		/* Skip already-added devices */
 		if (pci_dev_is_added(dev))
 			continue;
 		pci_bus_add_device(dev);
 	}

 	list_for_each_entry(dev, &bus->devices, bus_list) {
 		/* Skip if device attach failed */
 		if (!pci_dev_is_added(dev))
 			continue;
 		child = dev->subordinate;
 		if (child)
 			pci_bus_add_devices(child);
 	}
 }
 EXPORT_SYMBOL(pci_bus_add_devices);

 /** pci_walk_bus - walk devices on/under bus, calling callback.
  *  @top      bus whose devices should be walked
  *  @cb       callback to be called for each device found
  *  @userdata arbitrary pointer to be passed to callback.
  *
  *  Walk the given bus, including any bridged devices
  *  on buses under this bus.  Call the provided callback
  *  on each device found.
  *
  *  We check the return of @cb each time. If it returns anything
  *  other than 0, we break out.
  *
  */
 void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *, void *),
 		  void *userdata)
 {
 	struct pci_dev *dev;
 	struct pci_bus *bus;
 	struct list_head *next;
 	int retval;

 	bus = top;
 	down_read(&pci_bus_sem);
 	next = top->devices.next;
 	for (;;) {
 		if (next == &bus->devices) {
 			/* end of this bus, go up or finish */
 			if (bus == top)
 				break;
 			next = bus->self->bus_list.next;
 			bus = bus->self->bus;
 			continue;
 		}
 		dev = list_entry(next, struct pci_dev, bus_list);
 		if (dev->subordinate) {
 			/* this is a pci-pci bridge, do its devices next */
 			next = dev->subordinate->devices.next;
 			bus = dev->subordinate;
 		} else
 			next = dev->bus_list.next;

 		retval = cb(dev, userdata);
 		if (retval)
 			break;
 	}
 	up_read(&pci_bus_sem);
 }
 EXPORT_SYMBOL_GPL(pci_walk_bus);

 struct pci_bus *pci_bus_get(struct pci_bus *bus)
 {
 	if (bus)
 		get_device(&bus->dev);
 	return bus;
 }

 void pci_bus_put(struct pci_bus *bus)
 {
 	if (bus)
 		put_device(&bus->dev);
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* From setup-res.c, by:
	* Dave Rusling (david.rusling@reo.mts.dec.com)
	* David Mosberger (davidm@cs.arizona.edu)
	* David Miller (davem@redhat.com)
	* Ivan Kokshaysky (ink@jurassic.park.msu.ru)
	*/
	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/pci.h>
	#include <linux/errno.h>
	#include <linux/ioport.h>
	#include <linux/proc_fs.h>
	#include <linux/slab.h>

	#include "pci.h"

	void pci_add_resource_offset(struct list_head resources, struct resource res,
	resource_size_t offset)
	{
	struct resource_entry *entry;

	entry = resource_list_create_entry(res, 0);
	if (!entry) {
	pr_err("PCI: can't add host bridge window %pR\n", res);
	return;
	}

	entry->offset = offset;
	resource_list_add_tail(entry, resources);
	}
	EXPORT_SYMBOL(pci_add_resource_offset);

	void pci_add_resource(struct list_head resources, struct resource res)
	{
	pci_add_resource_offset(resources, res, 0);
	}
	EXPORT_SYMBOL(pci_add_resource);

	void pci_free_resource_list(struct list_head *resources)
	{
	resource_list_free(resources);
	}
	EXPORT_SYMBOL(pci_free_resource_list);

	void pci_bus_add_resource(struct pci_bus bus, struct resource res,
	unsigned int flags)
	{
	struct pci_bus_resource *bus_res;

	bus_res = kzalloc(sizeof(struct pci_bus_resource), GFP_KERNEL);
	if (!bus_res) {
	dev_err(&bus->dev, "can't add %pR resource\n", res);
	return;
	}

	bus_res->res = res;
	bus_res->flags = flags;
	list_add_tail(&bus_res->list, &bus->resources);
	}

	struct resource pci_bus_resource_n(const struct pci_bus bus, int n)
	{
	struct pci_bus_resource *bus_res;

	if (n < PCI_BRIDGE_RESOURCE_NUM)
	return bus->resource[n];

	n -= PCI_BRIDGE_RESOURCE_NUM;
	list_for_each_entry(bus_res, &bus->resources, list) {
	if (n-- == 0)
	return bus_res->res;
	}
	return NULL;
	}
	EXPORT_SYMBOL_GPL(pci_bus_resource_n);

	void pci_bus_remove_resource(struct pci_bus bus, struct resource res)
	{
	struct pci_bus_resource bus_res, tmp;
	int i;

	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++) {
	if (bus->resource[i] == res) {
	bus->resource[i] = NULL;
	return;
	}
	}

	list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
	if (bus_res->res == res) {
	list_del(&bus_res->list);
	kfree(bus_res);
	return;
	}
	}
	}

	void pci_bus_remove_resources(struct pci_bus *bus)
	{
	int i;
	struct pci_bus_resource bus_res, tmp;

	for (i = 0; i < PCI_BRIDGE_RESOURCE_NUM; i++)
	bus->resource[i] = NULL;

	list_for_each_entry_safe(bus_res, tmp, &bus->resources, list) {
	list_del(&bus_res->list);
	kfree(bus_res);
	}
	}

	int devm_request_pci_bus_resources(struct device *dev,
	struct list_head *resources)
	{
	struct resource_entry *win;
	struct resource parent, res;
	int err;

	resource_list_for_each_entry(win, resources) {
	res = win->res;
	switch (resource_type(res)) {
	case IORESOURCE_IO:
	parent = &ioport_resource;
	break;
	case IORESOURCE_MEM:
	parent = &iomem_resource;
	break;
	default:
	continue;
	}

	err = devm_request_resource(dev, parent, res);
	if (err)
	return err;
	}

	return 0;
	}
	EXPORT_SYMBOL_GPL(devm_request_pci_bus_resources);

	static struct pci_bus_region pci_32_bit = {0, 0xffffffffULL};
	#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
	static struct pci_bus_region pci_64_bit = {0,
	(pci_bus_addr_t) 0xffffffffffffffffULL};
	static struct pci_bus_region pci_high = {(pci_bus_addr_t) 0x100000000ULL,
	(pci_bus_addr_t) 0xffffffffffffffffULL};
	#endif

	/*
	* @res contains CPU addresses. Clip it so the corresponding bus addresses
	* on @bus are entirely within @region. This is used to control the bus
	* addresses of resources we allocate, e.g., we may need a resource that
	* can be mapped by a 32-bit BAR.
	*/
	static void pci_clip_resource_to_region(struct pci_bus *bus,
	struct resource *res,
	struct pci_bus_region *region)
	{
	struct pci_bus_region r;

	pcibios_resource_to_bus(bus, &r, res);
	if (r.start < region->start)
	r.start = region->start;
	if (r.end > region->end)
	r.end = region->end;

	if (r.end < r.start)
	res->end = res->start - 1;
	else
	pcibios_bus_to_resource(bus, res, &r);
	}

	static int pci_bus_alloc_from_region(struct pci_bus bus, struct resource res,
	resource_size_t size, resource_size_t align,
	resource_size_t min, unsigned long type_mask,
	resource_size_t (alignf)(void ,
	const struct resource *,
	resource_size_t,
	resource_size_t),
	void *alignf_data,
	struct pci_bus_region *region)
	{
	struct resource *r, avail;
	resource_size_t max;
	int ret;

	type_mask \|= IORESOURCE_TYPE_BITS;

	pci_bus_for_each_resource(bus, r) {
	resource_size_t min_used = min;

	if (!r)
	continue;

	/* type_mask must match */
	if ((res->flags ^ r->flags) & type_mask)
	continue;

	/* We cannot allocate a non-prefetching resource
	from a pre-fetching area */
	if ((r->flags & IORESOURCE_PREFETCH) &&
	!(res->flags & IORESOURCE_PREFETCH))
	continue;

	avail = *r;
	pci_clip_resource_to_region(bus, &avail, region);

	/*
	* "min" is typically PCIBIOS_MIN_IO or PCIBIOS_MIN_MEM to
	* protect badly documented motherboard resources, but if
	* this is an already-configured bridge window, its start
	* overrides "min".
	*/
	if (avail.start)
	min_used = avail.start;

	max = avail.end;

	/* Don't bother if available space isn't large enough */
	if (size > max - min_used + 1)
	continue;

	/* Ok, try it out.. */
	ret = allocate_resource(r, res, size, min_used, max,
	align, alignf, alignf_data);
	if (ret == 0)
	return 0;
	}
	return -ENOMEM;
	}

	/**
	* pci_bus_alloc_resource - allocate a resource from a parent bus
	* @bus: PCI bus
	* @res: resource to allocate
	* @size: size of resource to allocate
	* @align: alignment of resource to allocate
	* @min: minimum /proc/iomem address to allocate
	* @type_mask: IORESOURCE_* type flags
	* @alignf: resource alignment function
	* @alignf_data: data argument for resource alignment function
	*
	* Given the PCI bus a device resides on, the size, minimum address,
	* alignment and type, try to find an acceptable resource allocation
	* for a specific device resource.
	*/
	int pci_bus_alloc_resource(struct pci_bus bus, struct resource res,
	resource_size_t size, resource_size_t align,
	resource_size_t min, unsigned long type_mask,
	resource_size_t (alignf)(void ,
	const struct resource *,
	resource_size_t,
	resource_size_t),
	void *alignf_data)
	{
	#ifdef CONFIG_ARCH_DMA_ADDR_T_64BIT
	int rc;

	if (res->flags & IORESOURCE_MEM_64) {
	rc = pci_bus_alloc_from_region(bus, res, size, align, min,
	type_mask, alignf, alignf_data,
	&pci_high);
	if (rc == 0)
	return 0;

	return pci_bus_alloc_from_region(bus, res, size, align, min,
	type_mask, alignf, alignf_data,
	&pci_64_bit);
	}
	#endif

	return pci_bus_alloc_from_region(bus, res, size, align, min,
	type_mask, alignf, alignf_data,
	&pci_32_bit);
	}
	EXPORT_SYMBOL(pci_bus_alloc_resource);

	/*
	* The @idx resource of @dev should be a PCI-PCI bridge window. If this
	* resource fits inside a window of an upstream bridge, do nothing. If it
	* overlaps an upstream window but extends outside it, clip the resource so
	* it fits completely inside.
	*/
	bool pci_bus_clip_resource(struct pci_dev *dev, int idx)
	{
	struct pci_bus *bus = dev->bus;
	struct resource *res = &dev->resource[idx];
	struct resource orig_res = *res;
	struct resource *r;

	pci_bus_for_each_resource(bus, r) {
	resource_size_t start, end;

	if (!r)
	continue;

	if (resource_type(res) != resource_type(r))
	continue;

	start = max(r->start, res->start);
	end = min(r->end, res->end);

	if (start > end)
	continue; /* no overlap */

	if (res->start == start && res->end == end)
	return false; /* no change */

	res->start = start;
	res->end = end;
	res->flags &= ~IORESOURCE_UNSET;
	orig_res.flags &= ~IORESOURCE_UNSET;
	pci_info(dev, "%pR clipped to %pR\n", &orig_res, res);

	return true;
	}

	return false;
	}

	void __weak pcibios_resource_survey_bus(struct pci_bus *bus) { }

	void __weak pcibios_bus_add_device(struct pci_dev *pdev) { }

	/**
	* pci_bus_add_device - start driver for a single device
	* @dev: device to add
	*
	* This adds add sysfs entries and start device drivers
	*/
	void pci_bus_add_device(struct pci_dev *dev)
	{
	int retval;

	/*
	* Can not put in pci_device_add yet because resources
	* are not assigned yet for some devices.
	*/
	pcibios_bus_add_device(dev);
	pci_fixup_device(pci_fixup_final, dev);
	pci_create_sysfs_dev_files(dev);
	pci_proc_attach_device(dev);
	pci_bridge_d3_update(dev);

	dev->match_driver = true;
	retval = device_attach(&dev->dev);
	if (retval < 0 && retval != -EPROBE_DEFER)
	pci_warn(dev, "device attach failed (%d)\n", retval);

	pci_dev_assign_added(dev, true);
	}
	EXPORT_SYMBOL_GPL(pci_bus_add_device);

	/**
	* pci_bus_add_devices - start driver for PCI devices
	* @bus: bus to check for new devices
	*
	* Start driver for PCI devices and add some sysfs entries.
	*/
	void pci_bus_add_devices(const struct pci_bus *bus)
	{
	struct pci_dev *dev;
	struct pci_bus *child;

	list_for_each_entry(dev, &bus->devices, bus_list) {
	/* Skip already-added devices */
	if (pci_dev_is_added(dev))
	continue;
	pci_bus_add_device(dev);
	}

	list_for_each_entry(dev, &bus->devices, bus_list) {
	/* Skip if device attach failed */
	if (!pci_dev_is_added(dev))
	continue;
	child = dev->subordinate;
	if (child)
	pci_bus_add_devices(child);
	}
	}
	EXPORT_SYMBOL(pci_bus_add_devices);

	/** pci_walk_bus - walk devices on/under bus, calling callback.
	* @top bus whose devices should be walked
	* @cb callback to be called for each device found
	* @userdata arbitrary pointer to be passed to callback.
	*
	* Walk the given bus, including any bridged devices
	* on buses under this bus. Call the provided callback
	* on each device found.
	*
	* We check the return of @cb each time. If it returns anything
	* other than 0, we break out.
	*
	*/
	void pci_walk_bus(struct pci_bus top, int (cb)(struct pci_dev , void ),
	void *userdata)
	{
	struct pci_dev *dev;
	struct pci_bus *bus;
	struct list_head *next;
	int retval;

	bus = top;
	down_read(&pci_bus_sem);
	next = top->devices.next;
	for (;;) {
	if (next == &bus->devices) {
	/* end of this bus, go up or finish */
	if (bus == top)
	break;
	next = bus->self->bus_list.next;
	bus = bus->self->bus;
	continue;
	}
	dev = list_entry(next, struct pci_dev, bus_list);
	if (dev->subordinate) {
	/* this is a pci-pci bridge, do its devices next */
	next = dev->subordinate->devices.next;
	bus = dev->subordinate;
	} else
	next = dev->bus_list.next;

	retval = cb(dev, userdata);
	if (retval)
	break;
	}
	up_read(&pci_bus_sem);
	}
	EXPORT_SYMBOL_GPL(pci_walk_bus);

	struct pci_bus pci_bus_get(struct pci_bus bus)
	{
	if (bus)
	get_device(&bus->dev);
	return bus;
	}

	void pci_bus_put(struct pci_bus *bus)
	{
	if (bus)
	put_device(&bus->dev);
	}