PCI: work around Stratus ftServer broken PCIe hierarchy

A PCIe downstream port is a P2P bridge.  Its secondary interface is
a link that should lead only to device 0 (unless ARI is enabled)[1], so
we don't probe for non-zero device numbers.

Some Stratus ftServer systems have a PCIe downstream port (02:00.0) that
leads to both an upstream port (03:00.0) and a downstream port (03:01.0),
and 03:01.0 has important devices below it:

  [0000:02]-+-00.0-[03-3c]--+-00.0-[04-09]--...
                            \-01.0-[0a-0d]--+-[USB]
                                            +-[NIC]
                                            +-...

Previously, we didn't enumerate device 03:01.0, so USB and the network
didn't work.  This patch adds a DMI quirk to scan all device numbers,
not just 0, below a downstream port.

Based on a patch by Prarit Bhargava.

[1] PCIe spec r3.0, sec 7.3.1

CC: Myron Stowe <mstowe@redhat.com>
CC: Don Dutile <ddutile@redhat.com>
CC: James Paradis <james.paradis@stratus.com>
CC: Matthew Wilcox <matthew.r.wilcox@intel.com>
CC: Jesse Barnes <jbarnes@virtuousgeek.org>
CC: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 5e1ca3c58a7d..2dc8675eea1a 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -10,6 +10,7 @@
 #include <linux/module.h>
 #include <linux/cpumask.h>
 #include <linux/pci-aspm.h>
+#include <asm-generic/pci-bridge.h>
 #include "pci.h"
 
 #define CARDBUS_LATENCY_TIMER   176     /* secondary latency timer */
@@ -1395,10 +1396,13 @@ static unsigned no_next_fn(struct pci_dev *dev, unsigned fn)
 static int only_one_child(struct pci_bus *bus)
 {
         struct pci_dev *parent = bus->self;
+
         if (!parent || !pci_is_pcie(parent))
                 return 0;
-        if (parent->pcie_type == PCI_EXP_TYPE_ROOT_PORT ||
-            parent->pcie_type == PCI_EXP_TYPE_DOWNSTREAM)
+        if (parent->pcie_type == PCI_EXP_TYPE_ROOT_PORT)
+                return 1;
+        if (parent->pcie_type == PCI_EXP_TYPE_DOWNSTREAM &&
+            !pci_has_flag(PCI_SCAN_ALL_PCIE_DEVS))
                 return 1;
         return 0;
 }