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 8c8def26bfaa ("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@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
drivers/pci/pci.c | 39 +++++++++++++++++++++++----------------
1 file changed, 23 insertions(+), 16 deletions(-)
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 1febe90831b4..99293fa40db9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -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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