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@gmai... 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; }