[PATCH v2 4/5] PCI: generic: Correct, and avoid overflow, in bus_max calculation.

David Daney
2015-09-17T22:02:41Z

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.

Update host-generic-pci.txt to clarify the semantics of the "reg"
property with respect to non-zero starting bus numbers.

Signed-off-by: David Daney <david.daney@cavium.com>
---
Change from v1: Added text to host-generic-pci.txt

Documentation/devicetree/bindings/pci/host-generic-pci.txt | 4 +++-
drivers/pci/host/pci-host-generic.c | 7 ++++---
2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/pci/host-generic-pci.txt b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
index cf3e205..105a968 100644
--- a/Documentation/devicetree/bindings/pci/host-generic-pci.txt
+++ b/Documentation/devicetree/bindings/pci/host-generic-pci.txt
@@ -34,7 +34,9 @@ Properties of the host controller node:
- #size-cells : Must be 2.

- reg : The Configuration Space base address and size, as accessed
- from the parent bus.
+ from the parent bus. The base address corresponds to
+ bus zero, even though the "bus-range" property may specify
+ a different starting bus number.

Properties of the /chosen node:
diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
index 77cf4bd..0a9c453 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);

--
1.9.1