PCI: Remove pci_find_parent_resource() use for allocation (f44116ae) · Commits · 戴 / test

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 ("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:

Bjorn Helgaas <bhelgaas@google.com> CC: Linus Torvalds <torvalds@linux-foundation.org>

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;
		}

		/**

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