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>

Documentation/kernel-parameters.txt

@@ -2161,6 +2161,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 				on: Turn realloc on
 		realloc		same as realloc=on
 		noari		do not use PCIe ARI.
+		pcie_scan_all	Scan all possible PCIe devices.  Otherwise we
+				only look for one device below a PCIe downstream
+				port.
 
 	pcie_aspm=	[PCIE] Forcibly enable or disable PCIe Active State Power
 			Management.

arch/x86/pci/common.c

@@ -11,6 +11,7 @@
 #include <linux/dmi.h>
 #include <linux/slab.h>
 
+#include <asm-generic/pci-bridge.h>
 #include <asm/acpi.h>
 #include <asm/segment.h>
 #include <asm/io.h>
@@ -229,6 +230,14 @@ static int __devinit assign_all_busses(const struct dmi_system_id *d)
 }
 #endif
 
+static int __devinit set_scan_all(const struct dmi_system_id *d)
+{
+	printk(KERN_INFO "PCI: %s detected, enabling pci=pcie_scan_all\n",
+	       d->ident);
+	pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
+	return 0;
+}
+
 static const struct dmi_system_id __devinitconst pciprobe_dmi_table[] = {
 #ifdef __i386__
 /*
@@ -420,6 +429,13 @@ static const struct dmi_system_id __devinitconst pciprobe_dmi_table[] = {
 			DMI_MATCH(DMI_PRODUCT_NAME, "ProLiant DL585 G2"),
 		},
 	},
+	{
+		.callback = set_scan_all,
+		.ident = "Stratus/NEC ftServer",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "ftServer"),
+		},
+	},
 	{}
 };
 

drivers/pci/pci.c

@@ -22,6 +22,7 @@
 #include <linux/interrupt.h>
 #include <linux/device.h>
 #include <linux/pm_runtime.h>
+#include <asm-generic/pci-bridge.h>
 #include <asm/setup.h>
 #include "pci.h"
 
@@ -3893,6 +3894,8 @@ static int __init pci_setup(char *str)
 				pcie_bus_config = PCIE_BUS_PERFORMANCE;
 			} else if (!strncmp(str, "pcie_bus_peer2peer", 18)) {
 				pcie_bus_config = PCIE_BUS_PEER2PEER;
+			} else if (!strncmp(str, "pcie_scan_all", 13)) {
+				pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS);
 			} else {
 				printk(KERN_ERR "PCI: Unknown option `%s'\n",
 						str);

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;
 }

include/asm-generic/pci-bridge.h

@@ -30,6 +30,12 @@ enum {
 	PCI_ENABLE_PROC_DOMAINS	= 0x00000010,
 	/* ... except for domain 0 */
 	PCI_COMPAT_DOMAIN_0	= 0x00000020,
+
+	/* PCIe downstream ports are bridges that normally lead to only a
+	 * device 0, but if this is set, we scan all possible devices, not
+	 * just device 0.
+	 */
+	PCI_SCAN_ALL_PCIE_DEVS	= 0x00000040,
 };
 
 #ifdef CONFIG_PCI