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/uapi/asm-generic/swab.h

#ifndef _ASM_GENERIC_SWAB_H
#define _ASM_GENERIC_SWAB_H

#include <asm/bitsperlong.h>

/*
 * 32 bit architectures typically (but not always) want to
 * set __SWAB_64_THRU_32__. In user space, this is only
 * valid if the compiler supports 64 bit data types.
 */

#if __BITS_PER_LONG == 32
#if defined(__GNUC__) && !defined(__STRICT_ANSI__) || defined(__KERNEL__)
#define __SWAB_64_THRU_32__
#endif
#endif

#endif /* _ASM_GENERIC_SWAB_H */