PCI/ASPM: Handle PCI-to-PCIe bridges as roots of PCIe hierarchies

In a struct pcie_link_state, link->root points to the pcie_link_state of
the root of the PCIe hierarchy.  For the topmost link, this points to
itself (link->root = link).  For others, we copy the pointer from the
parent (link->root = link->parent->root).

Previously we recognized that Root Ports originated PCIe hierarchies, but
we treated PCI/PCI-X to PCIe Bridges as being in the middle of the
hierarchy, and when we tried to copy the pointer from link->parent->root,
there was no parent, and we dereferenced a NULL pointer:

  BUG: unable to handle kernel NULL pointer dereference at 0000000000000090
  IP: [<ffffffff9e424350>] pcie_aspm_init_link_state+0x170/0x820

Recognize that PCI/PCI-X to PCIe Bridges originate PCIe hierarchies just
like Root Ports do, so link->root for these devices should also point to
itself.

Fixes: 51ebfc92b72b ("PCI: Enumerate switches below PCI-to-PCIe bridges")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=193411
Link: https://bugzilla.opensuse.org/show_bug.cgi?id=1022181
Tested-by: lists@ssl-mail.com
Tested-by: Jayachandran C. <jnair@caviumnetworks.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v4.2+

path: root/include/net/Space.h

/* A unified ethernet device probe.  This is the easiest way to have every
 * ethernet adaptor have the name "eth[0123...]".
 */

struct net_device *hp100_probe(int unit);
struct net_device *ultra_probe(int unit);
struct net_device *wd_probe(int unit);
struct net_device *ne_probe(int unit);
struct net_device *fmv18x_probe(int unit);
struct net_device *i82596_probe(int unit);
struct net_device *ni65_probe(int unit);
struct net_device *sonic_probe(int unit);
struct net_device *smc_init(int unit);
struct net_device *atarilance_probe(int unit);
struct net_device *sun3lance_probe(int unit);
struct net_device *sun3_82586_probe(int unit);
struct net_device *apne_probe(int unit);
struct net_device *cs89x0_probe(int unit);
struct net_device *mvme147lance_probe(int unit);
struct net_device *tc515_probe(int unit);
struct net_device *lance_probe(int unit);
struct net_device *mac8390_probe(int unit);
struct net_device *mac89x0_probe(int unit);
struct net_device *cops_probe(int unit);
struct net_device *ltpc_probe(void);

/* Fibre Channel adapters */
int iph5526_probe(struct net_device *dev);

/* SBNI adapters */
int sbni_probe(int unit);