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Lukas Wunner 80696f9914 PCI: pciehp: Tolerate Presence Detect hardwired to zero
The WiGig Bus Extension (WBE) specification allows tunneling PCIe over
IEEE 802.11.  A product implementing this spec is the wil6210 from
Wilocity (now part of Qualcomm Atheros).  It integrates a PCIe switch
with a wireless network adapter:

  00.0-+              [1ae9:0101]  Upstream Port
       +-00.0-+       [1ae9:0200]  Downstream Port
       |      +-00.0  [168c:0034]  Atheros AR9462 Wireless Network Adapter
       +-02.0         [1ae9:0201]  Downstream Port
       +-03.0         [1ae9:0201]  Downstream Port

Wirelessly attached devices presumably appear below the hotplug ports
with device ID [1ae9:0201].  Oddly, the Downstream Port [1ae9:0200]
leading to the wireless network adapter is likewise Hotplug Capable,
but has its Presence Detect State bit hardwired to zero.  Even if the
Link Active bit is set, Presence Detect is zero, so this cannot be
caused by in-band presence detection but only by broken hardware.

pciehp assumes an empty slot if Presence Detect State is zero,
regardless of Link Active being one.  Consequently, up until v4.18 it
removes the wireless network adapter in pciehp_resume().  From v4.19 it
already does so in pciehp_probe().

Be lenient towards broken hardware and assume the slot is occupied if
Link Active is set:  Introduce pciehp_card_present_or_link_active()
and use it in lieu of pciehp_get_adapter_status() everywhere, except
in pciehp_handle_presence_or_link_change() whose log messages depend
on which of Presence Detect State or Link Active is set.

Remove the Presence Detect State check from __pciehp_enable_slot()
because it is only called if either of Presence Detect State or Link
Active is set.

Caution: There is a possibility that broken hardware exists which has
working Presence Detect but hardwires Link Active to one.  On such
hardware the slot will now incorrectly be considered always occupied.
If such hardware is discovered, this commit can be rolled back and a
quirk can be added which sets is_hotplug_bridge = 0 for [1ae9:0200].

Link: https://bugzilla.kernel.org/show_bug.cgi?id=200839
Reported-and-tested-by: David Yang <mmyangfl@gmail.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Rajat Jain <rajatja@google.com>
Cc: Ashok Raj <ashok.raj@intel.com>
2018-09-18 17:52:15 -05:00
arch Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 08:02:46 -10:00
block blk-cgroup: increase number of supported policies 2018-09-11 10:59:53 -06:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto DMAengine updates for v4.19-rc1 2018-08-18 15:55:59 -07:00
Documentation Code of Conduct: Let's revamp it. 2018-09-16 11:42:28 -07:00
drivers PCI: pciehp: Tolerate Presence Detect hardwired to zero 2018-09-18 17:52:15 -05:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs fixes for four CIFS/SMB3 potential pointer overflow issues, one minor build fix, and a build warning cleanup 2018-09-14 19:33:42 -10:00
include Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 06:44:32 -10:00
init Kbuild updates for v4.19 (2nd) 2018-08-25 13:40:38 -07:00
ipc ipc/shm: properly return EIDRM in shm_lock() 2018-09-04 16:45:02 -07:00
kernel Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 08:00:37 -10:00
lib lib/Kconfig.debug: fix three typos in help text 2018-09-04 16:45:02 -07:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
mm overlayfs fixes for 4.19-rc4 2018-09-13 19:21:40 -10:00
net tipc: check return value of __tipc_dump_start() 2018-09-12 13:15:04 -07:00
samples samples/bpf: all XDP samples should unload xdp/bpf prog on SIGTERM 2018-08-16 21:55:32 +02:00
scripts Kbuild fixes for v4.19 2018-09-09 05:42:11 -07:00
security Revert "x86/mm/legacy: Populate the user page-table with user pgd's" 2018-09-14 17:08:45 +02:00
sound ALSA: hda: Fix several mismatch for register mask and value 2018-09-03 23:47:40 +02:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 06:44:32 -10:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Remove obsolete kvm_unmap_hva notifier backend 2018-09-07 15:06:02 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-09-15 06:39:09 -10:00
Makefile Linux 4.19-rc4 2018-09-16 11:52:37 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.