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Subject[PATCH 5.4 11/80] PCI: Do not use bus number zero from EA capability
Date
From: Subbaraya Sundeep <sbhatta@marvell.com>

commit 73884a7082f466ce6686bb8dd7e6571dd42313b4 upstream.

As per PCIe r5.0, sec 7.8.5.2, fixed bus numbers of a bridge must be zero
when no function that uses EA is located behind it. Hence, if EA supplies
bus numbers of zero, assign bus numbers normally. A secondary bus can
never have a bus number of zero, so setting a bridge's Secondary Bus Number
to zero makes downstream devices unreachable.

[bhelgaas: retain bool return value so "zero is invalid" logic is local]
Fixes: 2dbce5901179 ("PCI: Assign bus numbers present in EA capability for bridges")
Link: https://lore.kernel.org/r/1572850664-9861-1-git-send-email-sundeep.lkml@gmail.com
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/pci/probe.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1089,14 +1089,15 @@ static unsigned int pci_scan_child_bus_e
* @sec: updated with secondary bus number from EA
* @sub: updated with subordinate bus number from EA
*
- * If @dev is a bridge with EA capability, update @sec and @sub with
- * fixed bus numbers from the capability and return true. Otherwise,
- * return false.
+ * If @dev is a bridge with EA capability that specifies valid secondary
+ * and subordinate bus numbers, return true with the bus numbers in @sec
+ * and @sub. Otherwise return false.
*/
static bool pci_ea_fixed_busnrs(struct pci_dev *dev, u8 *sec, u8 *sub)
{
int ea, offset;
u32 dw;
+ u8 ea_sec, ea_sub;

if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
return false;
@@ -1108,8 +1109,13 @@ static bool pci_ea_fixed_busnrs(struct p

offset = ea + PCI_EA_FIRST_ENT;
pci_read_config_dword(dev, offset, &dw);
- *sec = dw & PCI_EA_SEC_BUS_MASK;
- *sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
+ ea_sec = dw & PCI_EA_SEC_BUS_MASK;
+ ea_sub = (dw & PCI_EA_SUB_BUS_MASK) >> PCI_EA_SUB_BUS_SHIFT;
+ if (ea_sec == 0 || ea_sub < ea_sec)
+ return false;
+
+ *sec = ea_sec;
+ *sub = ea_sub;
return true;
}


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