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Subject[PATCH] ACPI/PCI: Fix bus range comparation in pci_mcfg_lookup
The configuration data provided by an MCFG region (ie PCI segment and
bus range) may span multiple host bridges.

Current code in pci_mcfg_lookup() carries out an exact match of host
bridge bus range start value against the MCFG region(s) bus range start
value which would cause configurations like the following:

MCFG region:
bus range: 0x00~0xff.
segment: 0.

PCI host bridges configuration (segment numbers and bus ranges):
host bridge 1:
bus range: 0x00~0x1f.
segment: 0.
host bridge 2:
bus range: 0x20~0x4f.
segment: 0.

to fail, in that the bus range start value for host bridge 2 does
not match the bus range start value of the respective MCFG region.

Relax the bus range check in pci_mcfg_lookup() to cater for
PCI configurations with multiple host bridges sharing the same
MCFG region.

Signed-off-by: Zhou Wang <>
Reviewed-by: Tomasz Nowicki <>
Acked-by: Lorenzo Pieralisi <>
drivers/acpi/pci_mcfg.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
index a6a4cea..2944353 100644
--- a/drivers/acpi/pci_mcfg.c
+++ b/drivers/acpi/pci_mcfg.c
@@ -195,11 +195,10 @@ int pci_mcfg_lookup(struct acpi_pci_root *root, struct resource *cfgres,
goto skip_lookup;

- * We expect exact match, unless MCFG entry end bus covers more than
- * specified by caller.
+ * We expect the range in bus_res in the coverage of MCFG bus range.
list_for_each_entry(e, &pci_mcfg_list, list) {
- if (e->segment == seg && e->bus_start == bus_res->start &&
+ if (e->segment == seg && e->bus_start <= bus_res->start &&
e->bus_end >= bus_res->end) {
root->mcfg_addr = e->addr;
 \ /
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