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Commit f44116ae authored by Bjorn Helgaas's avatar Bjorn Helgaas
Browse files

PCI: Remove pci_find_parent_resource() use for allocation 

If the resource hasn't been allocated yet, pci_find_parent_resource() is
documented as returning the region "where it should be allocated from."
This is impossible in general because there may be several candidates: a
prefetchable BAR can be put in either a prefetchable or non-prefetchable
window, a transparent bridge may have overlapping positively- and
subtractively-decoded windows, and a root bus may have several windows of
the same type.

Allocation should be done by pci_bus_alloc_resource(), which iterates
through all bus resources and looks for the best match, e.g., one with the
desired prefetchability attributes, and falls back to less-desired
possibilities.

The only valid use of pci_find_parent_resource() is to find the parent of
an already-allocated resource so we can claim it via request_resource(),
and all we need for that is a bus region of the correct type that contains
the resource.

Note that like 8c8def26 ("PCI: allow matching of prefetchable resources
to non-prefetchable windows"), this depends on pci_bus_for_each_resource()
iterating through positively-decoded regions before subtractively-decoded
ones.  We prefer not to return a subtractively-decoded region because
requesting from it will likely conflict with the overlapping positively-
decoded window (see Launchpad report below).

Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/424142


Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
parent d19cb803

drivers/pci/pci.c

+23 −16
Original line number Diff line number Diff line
@@ -401,33 +401,40 @@ EXPORT_SYMBOL_GPL(pci_find_ht_capability); 
 * @res: child resource record for which parent is sought

 *

 *  For given resource region of given device, return the resource

 *  region of parent bus the given region is contained in or where

 *  it should be allocated from.

 *  region of parent bus the given region is contained in.

 */

struct resource *

pci_find_parent_resource(const struct pci_dev *dev, struct resource *res)

{

	const struct pci_bus *bus = dev->bus;

	struct resource *r;

	int i;

	struct resource *best = NULL, *r;



	pci_bus_for_each_resource(bus, r, i) {

		if (!r)

			continue;

		if (res->start && !(res->start >= r->start && res->end <= r->end))

			continue;	/* Not contained */

		if ((res->flags ^ r->flags) & (IORESOURCE_IO | IORESOURCE_MEM))

			continue;	/* Wrong type */

		if (!((res->flags ^ r->flags) & IORESOURCE_PREFETCH))

			return r;	/* Exact match */

		/* We can't insert a non-prefetch resource inside a prefetchable parent .. */

		if (r->flags & IORESOURCE_PREFETCH)

			continue;

		/* .. but we can put a prefetchable resource inside a non-prefetchable one */

		if (!best)

			best = r;

		if (res->start && resource_contains(r, res)) {



			/*

			 * If the window is prefetchable but the BAR is

			 * not, the allocator made a mistake.

			 */

			if (r->flags & IORESOURCE_PREFETCH &&

			    !(res->flags & IORESOURCE_PREFETCH))

				return NULL;



			/*

			 * If we're below a transparent bridge, there may

			 * be both a positively-decoded aperture and a

			 * subtractively-decoded region that contain the BAR.

			 * We want the positively-decoded one, so this depends

			 * on pci_bus_for_each_resource() giving us those

			 * first.

			 */

			return r;

		}

	return best;

	}

	return NULL;

}



/**