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/sound/soc/dwc/Kconfig

config SND_DESIGNWARE_I2S
	tristate "Synopsys I2S Device Driver"
	depends on CLKDEV_LOOKUP
	select SND_SOC_GENERIC_DMAENGINE_PCM
	help
	 Say Y or M if you want to add support for I2S driver for
	 Synopsys desigwnware I2S device. The device supports upto
	 maximum of 8 channels each for play and record.

config SND_DESIGNWARE_PCM
	tristate "PCM PIO extension for I2S driver"
	depends on SND_DESIGNWARE_I2S
	help
	 Say Y, M or N if you want to add a custom ALSA extension that registers
	 a PCM and uses PIO to transfer data.

	 This functionality is specially suited for I2S devices that don't have
	 DMA support.