[PATCH 4/6] PCI: generic: Correct, and avoid overflow, in bus_max calculation.

[David Daney <ddaney.cavm@gmail.com>]

From: David Daney <david.daney@cavium.com>

There are two problems with the bus_max calculation:

1) The u8 data type can overflow for large config space windows.

2) The calculation is incorrect for a bus range that doesn't start at
   zero.

Since the configuration space is relative to bus zero, make bus_max
just be the size of the config window scaled by bus_shift.  Then clamp
it to a maximum of 255, per PCI.  Use a data type of int to avoid
overflow problems.

Signed-off-by: David Daney <david.daney@cavium.com>
---
 drivers/pci/host/pci-host-generic.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
index cd6f898..fce5bf7 100644
--- a/drivers/pci/host/pci-host-generic.c
+++ b/drivers/pci/host/pci-host-generic.c
@@ -164,7 +164,7 @@ out_release_res:
 static int gen_pci_parse_map_cfg_windows(struct gen_pci *pci)
 {
 	int err;
-	u8 bus_max;
+	int bus_max;
 	resource_size_t busn;
 	struct resource *bus_range;
 	struct device *dev = pci->host.dev.parent;
@@ -177,8 +177,9 @@ static int gen_pci_parse_map_cfg_windows(struct gen_pci *pci)
 	}
 
 	/* Limit the bus-range to fit within reg */
-	bus_max = pci->cfg.bus_range->start +
-		  (resource_size(&pci->cfg.res) >> pci->cfg.ops.bus_shift) - 1;
+	bus_max = (resource_size(&pci->cfg.res) >> pci->cfg.ops.bus_shift) - 1;
+	if (bus_max > 255)
+		bus_max = 255;
 	pci->cfg.bus_range->end = min_t(resource_size_t,
 					pci->cfg.bus_range->end, bus_max);
 
-- 
1.7.11.7