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/dt-bindings/power/r8a7779-sysc.h

/*
 * Copyright (C) 2016 Glider bvba
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2 of the License.
 */
#ifndef __DT_BINDINGS_POWER_R8A7779_SYSC_H__
#define __DT_BINDINGS_POWER_R8A7779_SYSC_H__

/*
 * These power domain indices match the numbers of the interrupt bits
 * representing the power areas in the various Interrupt Registers
 * (e.g. SYSCISR, Interrupt Status Register)
 */

#define R8A7779_PD_ARM1			 1
#define R8A7779_PD_ARM2			 2
#define R8A7779_PD_ARM3			 3
#define R8A7779_PD_SGX			20
#define R8A7779_PD_VDP			21
#define R8A7779_PD_IMP			24

/* Always-on power area */
#define R8A7779_PD_ALWAYS_ON		32

#endif /* __DT_BINDINGS_POWER_R8A7779_SYSC_H__ */